Notes Fisheries Chapters 4 to 7

1.4 Harvesting methods of following marine forms

                                

(Contents- a)Harpadon, b) Mackerel, c) Lobster, d) Pearl oyster)

1.4. a) BOMBAY DUCK or bummalo (Harpadon nehereus)

The local names in different states for Bombay duck or bummalo (Harpadon nehereus) are as in  Bengali: bamaloh or loytta, Gujarati: bumla, Marathi: bombil, Sinhala: bombeli, is, despite its name, not a duck but a lizardfish. In Mumbai, Konkan, and the western coastal areas in India, this dish is popularly known as "Bombil fry". It is native to the waters between Mumbai (formerly Bombay) and Kutch in the Arabian Sea, and a small number are also found in the Bay of Bengal. Great numbers are also caught in the South China Sea. The fish is often dried and salted before it is consumed, as its meat does not have a distinctive taste of its own. After drying, the odour of the fish is extremely powerful, and it is usually transported in air-tight containers. Fresh fish are usually fried and served as a starter.

The Bombay duck fishery, supported by a single species, Harpodon nehereus, contributes to about 10% of the estimated average annual marine landings of India. With a peculiar discontinuous distribution of the species, the fishery is of utmost importance in two maritime States of India, Gujarat and Maharashtra, where over 98% of the all-India Bombay duck catches are landed. In fact, from the bulk of the landings and the economic returns, the Bombay duck fishery in Gujarat and Maharashtra is equivalent to oil sardine and mackerel fisheries in Mysore and Kerala States.

Distribution:

                It has wide discontinuous distribution along the coast of East Africa, Indian subcontinent, Malaysia, Indonesia and China. In India it is taken in large quantities on the south and southeast coasts of Saurashtra, on the Gujarat coast and the Konkan coast of Maharashtra. It is also taken in appreciable quantities on the Andhra Orissa coasts and from the estuaries of Bengal. The discontinuous distribution of Bombay duck along the coasts of India has been attributed to various factors, the principal ones being the distribution and movements of various food components, variation of salinity along the coast, the 700F isotherm barrier of July etc. It is felt that the presence of low surface temperature in the area of occurrence is primarily responsible for peculiar distribution of the species.

In view of peculiar distribution of the fishery, it is essential to determine, whether, Bombay duck occurring on the east and west coasts of India belong to the same stock or they originate from more than one stock; in order to avoid depletion of the fishery due to intensive exploitation.

Biology

                 The presence of immature, maturing, gravid and spent individuals throughout the year shows that Bombay-duck is a continuous spawner. The Bombay duck shows two peak spawning periods, May-July and November-December, have been noticed. Spawning areas are not known and eggs average total length at attainment of sexual maturity is 230 mm and the male female ratio shows a progressive decline in number of males with increase in size or age. A new recruit spawner takes seven months to complete first spawning, second spawning cycle is complete in nine months, the third in ten months and the fourth in eleven months. The mean total lengths at these spawning are 252 mm, 305.5 mm, 347.5 mm and 372.5 mm respectively. The index of reproductive stress gives a value of 0.54, which is suggestive of low reproductive stress for recruit spawners. Fecundity increased with length and linearly with weight by reduction in ova size signifying that the somatic growth occupies a small segment of adult growth life. Intensive fishing in near shore areas permits a fish to spawn only twice resulting in average egg production of 1,15,011 during the effective life span. Though bimodality is seen in the distribution of oocytes, they develop in paired manner. Complete absence of ripe ova in the spent ovary indicates that Bombay-duck is a total spawner. Recruitment to the fishery is continuous; age at recruitment is 0.28 years and the age at selection 0.41 years.

Fig.4.1 Bombay duck External features.

            The Bombay duck feed on more than ten prey species. The final grading shows that the juveniles of Bombay-duck ranked first followed by non-penaeid prawns thereby, confirming that Bombay-duck is cannibalistic. The Bombay-duck is a multistage population in which number of broods contributes to the biomass in a year. On an average, five broods originate each year at an approximate interval of two months. The average length growth values indicate that the fish attains a total length of 165 mm in first year, 264 mm in second year, 330 mm in third year and 372 mm in fourth year. The effective life span in the inshore areas is 2.5 years.

Landings of Bombay duck:

The catch statics indicate a remarkable increase in landings from 7262 tonnes in 1951 to 1,28,618 tonnes in 1956. In 1958 and 1959 recorded poor landings. The fishery revived in 1960 and since then it has more or less stabilized around 80,000 tonnes comprising 80% of the catch of immature fish. 80% of total Bombay duck landings come from the west coast of India, which exclusively from the States of Gujarat and Maharashtra. In 1989, 1,30,689 tonnes have been landed.

Composition of commercial catch:

A study of sex ratio indicated that females predominant the catches throughout the year except in the month of July and August, where male predominates. In view of the continued breeding habits, the recruitment to the stocks is also continuous and is not restricted to definite periods. The fish appears to attain an average length of 127mm at the end of the first year and 210mm at the end of the second year. The frequent appearance of the '0' class shows that the recruitment is continuous and is more pronounced during the post monsoon period i.e. September-December.

Shoaling behavior:

The wanderings of the Bombay duck, which bring about fisheries of much regional importance along certain coasts seem to be influenced by two main factors i.e. the availability of food and the favorable condition of the water temperature. The low surface temperature in the areas of occurrence is probably responsible for the peculiar distribution of the species to a great extent than the other factors.

Harvesting: For harvesting of Bombay duck following fishery techniques are:

Gears and crafts used:

In south and southeast coast of Saurashtra, about 400-500 boats operate in the area during the fishing season, each boat carrying 7-9 fishermen. They operate 'Dol' nets 6-12 miles from the coasts in water of 10-15 fathoms deep. The majority of fishermen operate two nets at a time from each boat, but some units operate three nets.

The fishermen of Gujarat coast from Kosmba to Kolak fish for Bombay duck by gill nets along a stretch of 10 miles of coast line in inshore water during the months of June to September. These gill nets are 30 feet long and 3 feet high with a mesh of one inch from knot to knot.

The fishermen of Konkan coast from Kalai (South of Daman) to Waroda operate 'Dot' nets of various sizes in waters ranging in depths from 6-10 fathoms.

The fishermen of Andhra-Orissa coast harvest Bombay duck in boat seines and fixed bag nets operated by two catamarans.

Disposal of catch:

A portion of the catch is used as a food when fresh, but the bulk of it is sun dried. Being a very soft fish it is easily spoiled. When the landings arrive late the catch is very often not in fit condition for human consumption and is forced to be converted into manure. The fish is sun dried on specially erected bambo scaffoldings.

Non laminated Bombay duck

Sun drying of Bombay duck on scaffolds is the traditional method of preservation of the fish on the Maharashtra and the Gujarat coasts. The fish after being washed in sea water is locked in pairs at the jaws and hung on ropes tied between poles to be dried in the natural breeze and heat. Complete drying of the product requires 3-5 days depending on the weather conditions. After 3-4 days the fish is removed from the scaffolds and further dried by spreading on Palmyra mats.

Laminated Bombay ducks:

Fresh fish are washed in water containing 1-2 per cent salt and 0.05-0.1 per cent citric acid. The fish flattened by longitudinal cuts to remove entrails and vertebral column and spread over wire mesh trays on bamboo platforms and dried in sun till the moisture content is brought down to 10%. The laminated fish is pressed individually by passing through a roller press. The individual pieces are trimmed into uniform size and shape.

1.4.b)  INDIAN MACKERELS - Rastrelliger kanagurta

Local Names: Ayala ,  Ayila (Malayalam),  Ailai ,  Augalai (Tamil),  Bangada (Canarese),  Indian mackerel ,  Kaula gedar (Marathi),  Kanagurta (Telugu),  Kanangeluthi (Tamil),  Kannangadatha (Telugu) ,  Kumla (Tamil),  Karan-kita (Oriya),  Oibia gedar (Sindhi),  Bangadi (Hindi).

Amongst the marine bony fishes of India, mackerels enjoy the first position in importance as a commercial group contributing-high tonnage per year. The Indian mackerels, Rastrelliger kanagurta, are the only species of the genus found in the seas around the sub-continent. It belongs to the family Scombridae (order: Percifornies). It is an important commercial fish of the west coast of India. The commercial landings are mainly composed of only one species, R. kariagurta, and another species, R. brachysoflia, is found in the Andaman waters but forms only a small part of the catch. Mackerels constitute 15-18% of the total marine fish landings in India, 90% of this comes from the west coast, mainly from Quilon in Kerala to Ratnagiri in Maharashtra.

The chief centre of mackerel fishery is the area between Ratnagiri in Bombay and Quilon in Kerala State. On the east coast, it appears sporadically near Mandapam, Madras, Kakinada, Vishakhapatnam and parts of Orissa.

Habit and Habitat: The Indian mackerel is a surface feeder, feeding on phyto and zooplankton that are filtered by the well developed gill rakers. Two periods of feeding intensified have been observed October-December, and March-April. Among the adults, the feeding intensity was found high during maturing stages, low in mature and spawning individuals, and again high in spent and recovering ones. Only a single species of mackerel, Rastrelliger kanagurta (Scomber nzicrolepidotus) supports the mackerel fishery. This species is found throughout the Pacific and Indian Oceans. It is pelagic and planktophagus, feeding mostly on both zooplankton and phytoplankton. The rich plankton crop of the inshore waters, following the monsoon, attracts the mackerels from off shore, and these move in large shoals shorewards.

 . 4.3. Mackerel

Diagnostic features:

1.       Body moderately deep, its depth at margin of gill cover 4.3 to 5.2 times in fork length; head longer than body depth.

2.       Maxilla partly concealed, covered by the lacrimal bone, but extending to about hind margin of eye; 

3.       Gill rakers very long, visible when mouth is opened, 30 to 46 on lower limb of first arch; a moderate number of bristles on longest gill raker, 105 on one side in specimens of 12.7 cm, 140 in specimens of 16 cm, and 160 in specimens of 19 cm fork length. 

4.       Intestine 1.4 to 1.8 times fork length.   

5.       Colour: narrow dark longitudinal bands on upper part of body (golden in fresh specimens) and a black spot on body near lower margin of pectoral fin;

6.       Dorsal fins yellowish with black tips, caudal and pectoral fins yellowish; other fins dusky. 

7.       Maximum fork length is 35 cm, common to 25 cm; in Philippine waters, length at first maturity is about 23 cm and about 4.5 kg. in weight.

8.       The shoals of mackerels are easily identified and located even from a distance. During the day time the shoals, appearing as patches, are dark with ripples, while at night these patches emit a phosphorescent glow. Generally the shoals are composed of large numbers of individuals belonging to the same age group and consequently having same size.

9.       The feeding intensity increases with maturity, and it is low in both juveniles as well as spawners.

10.   The fish measures 10 cm in the first year, but attains 18 cm at the end of the second year. The fish attains 22.4 cm at the first spawning.

11.   No sexual dimorphism occurs.

12.   Spawning occurs in succession; starting from April it lasts up to September.

13.   The fish attains maturity when about two year old and 19-22 cm in length. But the mackerel of the Andaman Island is reported to attain maturity in the third year of its life; at a length of 25-26 cm.

14.    Spawning: Studies based on gonad examination and ova diameter suggest that the mackerel spawns round the year, with regional difference in the period of commencement, duration and termination of spawning. Along the west coast, spawning commences in March, and is terminated by September or October, the period of intensive spawning being June to August. Along the east coast, and Andaman Island, the spawning commences in October-November, and ends in April-May.

15.   Fecundity: It has been suggested that the ova are liberated in three batches in a single spawning season, and fecundity is 94,000 to 1, 10,000 eggs.

Harvesting: Fishing season extends from October to February, after which the shoals break up and disappear for a short period. Fishing is carried out up to a depth of 25 m and mostly consists of juveniles ranging from 160-180 mm. The fish move in shoals from offshore to inshore waters, possibly for feeding on plankton. Mackerels also enter the river mouths, estuaries and backwaters. Delay in monsoon causes delay in fishing season.

Fishing is carried out by boat seines, drag nets, gill net, drift net and cast net. Of these the    Rampani net is the most efficient in catching large shoals of fish.

                 i.        The craft used are dug-out canoes with boat-seines or Odam-vala or gill nets known as Ayila-chala-vala, both of local design and made by hand. The third area lies between Mangalore and Ratnagiri, also a busy centre for mackerel fishery. Here the season starts a little later, i.e., from  October to November, extending to February or March.

               ii.        Gill nets locally known as pattabcile and a highly specialized shore seine known as Rampani are in use for the capture of mackerels. Rampani is a long shore seine, operated by about 80 men and assisted by five dugout canoes.

             iii.       The indigenous boats and gears can operate in an area of four kilometers only from the shore.

              iv.       The fishing crafts used include boats with out-rigger (Pandi, Hodi) and dug-out canoes.

                v.       The gears used include boat seine (Odam vala, Pathu vala, Kolli vala), shore seine (Rampani), drift net (Pettle bale), gill net (ayila chela vala), cast net (Pag) etc.

              vi.       The catches are mostly composed of juveniles and immature individuals from 16 to 18 cm. 

            vii.       The mackerel fishery shows great fluctuations, the lowest catch during the period 1958—79, was 21,703 tonnes in 1968, the highest being 2, 04,575 tonnes in 1971, constituting 17.6% of the total marine catch. There appears to be a cyclical period of abundance and decline after every 4-5 years. 1980-84 was a slack period. In 1987, the catch was 78,896 tones. Maximum production comes from Karnataka followed by Kerala.

Processing and preservation: Mackerel is an excellent food fish, particularly when fresh. A large percentage (40%) of the catch is preserved in ice and dispatched to various inland towns by trains and truck. It is estimated that about 60% are salt-cured or picked, of which a portion is consumed in the country, while the balance is exported to nearby countries like Ceylon. When the catch is very abundant the surplus is converted into manure. The bulk of fins, gills and guts are utilized in the preparation of fish- meal.

Only a small part of the catch is consumed fresh, the major part is cured by salting or sun drying method.

Depending upon the transport facilities available, a portion of the mackerel landings is diverted from the fishing centers to local and Bombay markets for consumption in fresh state. About half the landing finds way to curing yards. Mackerels are salt-cured, pickled, smoked or canned. In the years of bumper landings, mackerels are used for production of fish meal for cattle or poultry use, and for manufacture of fish guano for use in coconut, coffee and tea plantations as manure.

1.4. c) LOBSTERS (Panulirus homarus)

Lobsters are pricey whether you purchase them locally or in the international market. This is a highly-priced marine crustacean. Lobsters can basically be divided into two namely rock lobsters and sand lobsters. Among rock lobsters Panulirus homarus, P. ornatus, P. versicolor and P. polyphagus have good export market, while only one species Thenus orientalis is in demand among sand lobsters. Rock lobsters are comparatively fast growing and highly adaptable to culture conditions. P. ornatus grows fast and attains a maximum size of 3.5 kg and is most suitable for fattening, whereas P. polyphagus and P. homarus attain sexual maturity early (around 175 g), grows to a maximum of 1.5 kg.

General Information: Marine crustacean farming is dominated by the shrimp species followed by crab culture. In India, the exclusive marine production of shrimps is not in vogue. However, in recent past lobster has turned out to be a potential candidate for mariculture. India earned Rs. 71.56 corers through export of lobster, mostly to Southeast Asian countries and Japan during 2005-06. Like crab farming lobster culture can either be either “farming” or “fattening” operations. Farming is essentially a grow-out operation in which the juveniles are grown for several months until they attain marketable size. Fattening, of the other hand, refers to short duration culture of undersized lobsters to a specific acceptable size and hence command better price.

                     

Fig.4.4. External features of P. homarus

Farming is carried out under closed-cycle and controlled aquaculture. In the past land based farming of lobsters has been severely hampered due to the lack of suitable technology and production method and only cage culture were found profitable. However, even in cage farming there are several impediments affecting the economic profitability such as cannibalism, need of heated water, lack of high quality dry feed, high labour cost and high investment costs. Asian countries are the forerunners in lobster farming especially Philippines and Singapore. India’s contribution to marine crustacean culture in general and lobster farming in particular is meager, however there is immense potential for states like Kerala, Tamil Nadu, Andhra Pradesh and Karnataka to take up lobster farming in a large way.

Stocking, Harvesting and Transport

The fingerlings should be weighed regularly. You can stock 10 lobsters weighing 150-200 grams in a 1-sq meter pen. To prevent defacing, the lobsters should be dropped carefully into the pen. Make sure that you do this when it’s high tide. Pick the one having the same sizes because these crustaceans are carnivorous. If you mix the small and large lobsters, the smaller ones can get eaten. Harvesting can be done after 6-10 months when the lobster is already 900 to 1,000 grams. You will need extra help if you maintain several pens.

Harvesting of lobsters from indoor grow-out system involves draining out water and picking up commercially grown lobsters. The lobsters (70-80g) attain marketable size (>250 g) over a period of five months. The harvested lobsters can be marketed either in whole cooked form or in live condition. For whole cooking, live lobsters are dipped in chilled water for few minutes until they die and then immersed in boiling water containing acetic and citric acid for few minutes. After cooking they are kept in chilled water and then cleaned, packed and blast frozen.

For live lobster transport, they are immobilized in chilled water for few minutes and then packed. For short term transportation to holding centers moist beach sand can be used. For long-term transport, the lobsters have to be packed in thermocol boxes as depicted in the illustration below.

These crustaceans can only be caught using gill nets and since the stocks are dependent on the catch, the price is really high. If you live in the coastal areas, you might want to invest in a lobster farm. Lobster farming is viable and lucrative so you will surely earn a lot of profits.

1.4. d) PEARL OYSTER  ( Pinctada sp.)

  

Pearl Culture

            Pearl is known to human beings since ancient times. Pearls are of animal origin and are obtained from Pearl oyster belonging to phylum Mollusca.

            Kokichi Mikimoto (1858-1954) is referred to be the father of pearl industry in Japan. In 1890 he established a pearl farm on a small Island of Taba and began to culture oysters but could not get success for two years. In the third year due to a red-tide his farm was destroyed completely except for a batch of some oysters which survived. Subsequently on 11th July 1893, his wife Uma when opened an oyster shell to her surprise and joy she found a pearl duly formed in int. It was a memorable day for them. Then in 1896 he got a patent for pearl culture.  Tokich Nishikawa, a Govt. scientist of Misaki Marine Biological Laboratory of Tokyo University, was the first person to get spherical artificial pearl.

Pearl Producing Molluscs and their Occurrence:

            The true pearl oyster belongs to the genus Pinctada (Roding) ,class - Sivaliva,  under the family Pteriidae, order Dysodonta. Members belonging to the Pteriidae family are characterized by a straight hinge with 1–2 small tooth-like thickening, a cavity below the anterior angle for the byssus, and usually a scaly surface of the outer shell valves.

Six species of pearl oysters, Pinctada fucata (Gould), P. margaritifera (Linnaeus), P. chemnitzii (Philippi), P. sugillata (Reeve), P. anomioides (Reeve) and P. atropurpurea (Dunker) occur along the Indian coasts. Their morphological characteristics are as follows:

Pinctada fucata (Gould)

The hinge is fairly long and its ratio to the broadest width of the shell is about 0.85 and that to the dorsoventral measurement is about 0.76. The left valve is deeper than the right. Hinge teeth are present in both valves, one each at the anterior and posterior ends of the ligament. The anterior ear is larger than in the other species., and the byssal notch, is slit-like. The posterior ear is fairly well developed. The outer surface of the shell valves is reddish or yellowish-brown with radiating rays of lighter colour. The nacreous layer is thick and has a bright golden-yellow metallic lustre.

Pinctada margaritifera (Linnaeus)

The hinge is shorter than the width of the shell and has no teeth. The anterior border of the shell extends in front of the anterior lobe. The byssal notch is broad. The anterior ear is well developed while the posterior ear and sinus are absent. The posterior end of the shell meets the hinge almost at a right angle. Shell valves are moderately convex. Externally, the shell is dark grayish-brown with radially disposed white spots. The nacreous layer is iridescent with a silvery lustre except distally where it is black. This pearl oyster is also known as the Black-lip pearl oyster due to the dark marginal colouration of the shell.

Pinctada chemnitzii (Philippi)

The hinge is almost as long as the antero-posterior measurement of the valves. The posterior ear is well developed and the convexity of the valves is less than in P. fucata. The anterior and posterior hinge teeth are present, the former is small and rounded and the latter prominent and ridge-like. The posterior ear and the posterior sinus are well developed. The shell valves are yellowish externally with about four or more light brownish radial markings from the umbo to the margin of the shell. The growth lines of the shell are broad. The nacreous layer is thin and bright, while the non-nacreous layer is yellowish-brown.

Pinctada sugillata (Reeve)

The hinge is considerably shorter than the antero-posterior axis of the shell with a ratio of 1:1.3. The anteroposterior measurement is almost equal to the dorso-ventral measurement. The anterior ear in both valves is small and the byssal notch is a moderately wide slit. The anterior ears are slightly bent towards the right. The posterior ear and sinus are poorly developed. The convexity of the valves is not prominent, especially that of the right valve. The hinge teeth are small and the posterior one is slightly elongated. The shell valves are reddish-brown with six yellowish radial markings.

Pinctada anomioides (Reeve)

The hinge is shorter than the width of the broadest region of the antero-posterior axis of the shell with a ratio of 1:1.2–1.5. The hinge and dorso-ventral axis have a ratio of 1:1.4. Hinge teeth are absent or poorly developed. The anterior ear is moderately developed and the byssal notch at its base is deep. The posterior ear and sinus are absent. The shell valves are translucent and externally yellowish or grayish.

Fig.4.5. External Features of a pearl oyster.

Pinctada atropurpurea (Dunker)

The shell is roundish and its hinge narrow. The valves are thin, translucent and moderately convex. A poorly developed anterior hinge tooth is present in some oysters. The shell valves are copper coloured.

Distribution

Pearl oysters of the genus Pinctada are widely distributed in the world. They occur in several seas of the tropical belt and in the sub-tropical region. The good quality and commercial value pearls are produced by, P. maxima, P. margaritifera and P. fucata.

In the Indian waters six species of pearl oysters occur but only P. fucata has contributed to the pearl fisheries in the Gulf of Mannar and Gulf of Kutch. In the Gulf of Mannar, the pearl oysters occur in large numbers on the submerged rocky or hard substrata known as paars. The paars lie at depths of 12 to 25 m off the Tuticorin coast along a stretch of 70 km. In the Palk Bay, P. fucata occurs sporadically on loose sandy substratum attached to submerged objects in littoral waters. In the Gulf of Kutch, the pearl oysters are found as stray individuals on the intertidal reefs known as khaddas. In the southwest coast of India at Vizhinjam, Kerala coast, large numbers of spat of P. fucata have been collected from mussel culture ropes. The blacklip pearl oyster, P. margaritifera is confined mostly to the Andaman Islands where it is common in some places. From Lakshadweep, settlement of spat of P. anomioides has been observed on the ridges of rocks and corals.

India has one of the highest demand for pearls for setting in jewellry, and is particularly famous for its pearl oyster resources which yield superb pearls. The pearl oyster fisheries are located in two main areas: 1) in the Gulf of Mannar off Tuticorin coast and 2) in the Gulf of Kutch on the northwest coast of the country. The pearl oysters are found in two different environments in the two localities, at depths up to 23 meters in the Gulf of Mannar, in the intertidal zone in the Gulf of Kutch. These bivalves form large beds on hard substrata in the Gulf of Mannar, while they are sparsely distributed in the Gulf of Kutch. The pearl oyster resources in the two areas have been fished for pearls until the early 1960's.

Madras Government Fisheries Department carried out preliminary research at the Marine Biological Station in Krusdai Island, Gulf of Mannar. Research focused mainly on the biology and ecology of several species. The oysters were reared in cages and induced to form pearls. In 1972 the Central Marine Fisheries Research Institute started a pearl culture research project at Tuticorin. Success came in July 1973 when a perfectly spherical pearl was produced.

Pearl culture under the Indian Council of Agricultural Research (ICAR) was implemented (from 1973–78) by the CMFRI in association with the Department of Fisheries, Government of Tamil Nadu.

The CMFRI also succeeded in artificially spawning Pinctada fucata, rearing of larvae, and producing seed in the laboratory by hatchery techniques. Recently the CMFRI also produced seed of the black-lip pearl oyster, Pinctada margaritifera which produces the highly valuable black pearl.

Tamil Nadu Fisheries Development Corporation and the Southern Petro-chemical Industries Corporation Ltd. established in 1983 a company to produce cultured pearls, with the farm at Krusadai and the nucleus implantation centre at nearby Mandapam.

 Pearl Producing Sites:

            The main sites of production of pearl are the Persian Gulf, Gulf of Mannar (Ceylon), Sulusea (near Philippines). Besides these coast of Australia and shores of Central America (Pennama Bay, Gulf of California) including islands of south Pacific are also important productive places. Now-a-days Japan has surpassed all the countries in the bulk of pearl production by invention of pearl culture techniques.

            The pearls oyster beds of the east coast of India are more extensive and productive than those of the west coast. These pearl beds produce best quality of pearls called as Lingha Pearl. The pearl oysters are obtained from the reefs in the Gulf of Mannar, Gulf of Kutch, Pak bay and Baroda.

            To study the mode of formation of pearl it is essential to know the structure of the shell and mantle. Shell of pearls oyster is composed of three distinct layers. They are as follows:

1.       Periostracum- It is an outer layer formed of a horny conchyolin which is a substance related to chitin. On its inner side the next layer is found which is known as prismatic layer.

Fig. 4.6.T.S. of Shell and mantle of a pearl oyster.

2.       Prismatic Layer: It is the middle layer secreted by mantle. This layer is made up of minute crystals of calcium carbonate, separated by thin layers of conchiolin.

3.       Nacreous layer: It is the inner-most layer formed of calcium carbonate and called as 'Mother of the pearl'. It consists of alternating layers of calcium carbonate and conchyolin arranged parallel to the surface. This nacreous layer is secreted by the entire outer surface of the mantle, while the first two layers are secreted only by the edge of the mantle.

Fig.4.7. Stages in pearl formation: A. Primary stage: B. Progressive Stage; C. Final Stage

Pearl Culture:

            Pearl oysters are found from the low tide level to depths of about 75 m, therefore they can adapt and live in varying environmental conditions within this range. Environmental factors such as bottom topography, wind, waves, water movement, current, light, temperature, salinity, dissolved oxygen, pH, nutrient salts, and primary production play a crucial role in the settlement, growth and reproductive pattern of oysters, both in the natural beds and farms. In the Gulf of Mannar, the pearl oysters live on rocky or other hard substrata which lie roughly in a line parallel with and at a distance of 10–16 km from the coast. A rich fauna, comprising members of various groups like sponges, hydroids, polychaetes, lamellibranchs, amphipods, decapods, echinoderms, fishes etc. are usually associated with pearl oyster beds. The oysters obtained from the beds are successfully reared in shallow coastal waters with depths ranging from 4–8 m, where the sea does not become rough. In farming the pearl oysters, the preferred depth of culture is about 10 m where silting should be minimal. Unlike in Japan, the variation in temperature and salinity is not much pronounced in the Gulf of Mannar. The temperature of seawater in the natural beds varies from 27.0 °C (January) to 32.5 °C (May) whereas in the oyster farm at Tuticorin, it fluctuates between 24.0–32.5 °C. Similarly, salinity in the natural beds fluctuates between 27.4 ‰ and 35.90 ‰ with an annual range of 8.5 ‰. The salinity values in the oyster culture site at Veppalodai, ranged between 32.15 ‰ and 33.50 ‰ during 1974–76.

According to Nishikawa’s theory, when any foreign particles enters in the body of the pearl oyster, it will give irritation and the animal will try to remove or neutralize the irritation, when mantle will secrete "Nacreous liquid" which on coming in contact with sea water solidifies and known as pearl.

Rearing pearl-oysters, seeding them with a nucleus and developing pearl is termed as a pearl culture. Pearl culture is done in natural climatic conditions in sea water under suitable depth and temperature. This whole process is very much complicated, technical and time taking and can be managed as given below:

I.                    Collection of oysters:

The oysters are collected from the bottom sea by the divers. Each diver4 has a small net at the time of diving. The net helps in the collection of oysters from the bottom. The whole collected oysters are stored and sorted out.

II.                 Rearing of Oysters

The collected oysters are first cleaned and then placed into the culture cages for a period of about 10 to 20 days to recover the strain due to excessive handling and to acclimatize to the shallow water conditions.

            The collected oysters are stocked and reared in special type of cages called as rearing cages. These cages are well protected from natural enemies of oysters like Octopus, Eel, Devil fishes etc.

III.               Insertion of nucleus:

The insertion of nucleus as foreign particle is very much technical process and is of great importance for pearl industry. Following steps are taken for the insertion of nucleus.

1.       Fitness of oyster for operation: For production of pearl healthy, aged and well developed oysters are chosen. These selected oysters are acclimatized in controlled conditions.

2.       Preparation of grant tissue:   The piece of tissue which is inserted inside the mantle is called 'graft' tissue. A strip of about 7 x 0.75 cm is cut from the edge of mantle of healthy oysters by sharp knife. This piece is smoothes, cleaned and washed off the adhering mucus and again wiped off by wet sponge. The border of gill piece is removed by sharp scalpel. Now this tissue is trimmed to 2 to 3 centimeters long narrow strip and again cut transversely into small squares according to the size of the nucleus for insertion. These squares are kept in sea water 22⁰C where they can survive for about 48 hours.

3.       Preparation nucleus: A series of experiments could show that the best nucleus is produced by the clam shell itself. This nucleus made up of shells have the same composition and density as that secreted by the mantle wall, so the nucleus and the pearl forming substances are homogenized and cannot be separated out easily.

4.       Insertion of nucleus: For the insertion of nucleus, oysters are fixed in a desk clamp in the position of right valve facing upward. Mantle folds are smoothly touched to expose the foot and the main body mass, followed by an incision into the epithelium of the foot and a slender channel into the channel and the nucleus is placed over the graft tissue which functions as a bed for the nucleus.

5.       Post operational care: Nucleated oysters are placed into cages and suspended into sea water and attached with floating rafts to a depth of 2 to 3 meters for about 6 to 7 days to recover from the shocks due to operation. This period is known as Recovery Period. Now oysters are examined properly 3600 nucleated oysters are kept in different cages suspended in sea water at 2 to 3 meters depth for 3 to 6 years and undisturbed except at the time of clearing and inspection.

IV.               Harvesting of Pearl:

1. Harvesting of pearls is done in winters from December to February. The oysters are brought to the dock, cleaned and harvested.  The oysters are collected by the expert divers and are cut open to obtain the jewel. It takes 2-4 years for developing a good sized pearl.
2. Harvesting the pearls is as important a process as seeding because oysters that produce a high quality pearl can be re-implanted with a new nucleus to produce another pearl. Harvesting of the cultured pearls is usually carried out manually. However, the process can be automated with the use of simple machines. In the case of manual extraction the pearls are collected by initially separating the two shell valves, by cutting the adductor muscle, making an incision on the gonad and squeezing the pearl out. The machines used for pearl extraction usually work by dissolving the oyster soft body parts with the use of chemicals while the pearls remain as they are and become easily extractable. In case the oysters need to be re-used for a second time, the pearls are carefully removed by opening the pearl-sac through the gonad taking care not to damage nor stress the oyster.
3. A seeding technician (often the same one that did the initial implant) makes an incision in the pearl sack and removes the pearl. The pearl is examined and if it is of a high quality, a new, larger nucleus is inserted into the pearl sac and the oyster is returned to the farm. Oysters can be re-implanted up to 2 times, each time with a nucleus the size of the harvested pearl. For example, if an initial nucleus of 5 mm diameter produces a 7 mm pearl, then a 7 mm nucleus can be re-implanted into the oyster. Because large-diameter pearls fetch a much higher price than smaller ones, the larger pearls produced by re-implantation eventually contribute greatly to the farm’s income
4. The oysters are then returned to the culture site for recovery, and after a certain length of time they can be operated for a second time to produce additional pearls. In Japan, harvesting is done during periods of low temperature and pH as the pearls tend to be of higher quality due to a thick and compact outer nacreous layer.
5. Finally, the harvested pearls are washed in distilled water, polished with refined salt and sorted for sale according to size, colour, shape, lustre and other external characteristics.
6. From each pearl oyster we obtain several products: cultured pearls, natural pearls, mother-of-pearl shell (to make buttons or sell as souvenirs) and also a tasty meat product known locally as "callo" (a variety of "scallop meat"). In the process of pearl culture nothing ever goes to waste.

Fig.4.8. Steps in Harvesting of Pearl Oysters 1. Oysters in cages, 2.Removing Oysters from cages, 3.Cleaning & Harvesting of Pearls,4. Pearl in mantle cavity of Oysters, 5. Harvested pearls.

V. Clearing of pearls:

            After taking out the pearls from the oysters shell they are washed properly, cleared with the soap solution, but pearls should not be rubbed much.

            The pearl is a small about 10 mm diameter. The pearl is rounded, flawlessly white, colored, pinkish, yellowish or bluish colored calcareous product.

Pearl fisheries in the Gulf of Mannar are under the control of Tamil Nadu Govt. The pearl fisheries are not operated regularly in Gulf of Mannar and the fishery is stopped since 1962. In past also, after a gap of 27 years the fishery was resumed in the year 1955 and continued up to 1962. During the period the average annual catch of oysters was 10.83 millions. The year 1958 was the best year, when 21.48 million oysters were collected giving a net income of Rs. 465 thousand to the State Govt. Pearl Oyster yields about Rs. 30,000 on an average per fishery in Gulf of Kutch.

Composition of pearl:

            Pearl comprises of water, organic matter, calcium carbonate and the residue.

1. Calcium Carbonate                 :           90%

2. Organic matter                       :           3.5 - 5.9%

3. Residue                                 :           0.1 - 0.8%

4. Water                                                :           2-4%

In India, the highest recorded production rate achieved in single implantation was about 65%, while in multiple implantation, a rate up to 180% has been obtained. This rate can definitely be improved by professional technicians with considerable knowledge and practical experience.

The gross production of pearls includes all kinds of pearls, from the finest quality to trash. Usually a small percentage of the pearls produced have an outstanding colouration and perfectly round shape, while a large proportion are inferior and some totally valueless as gems. This is a common feature in all pearl culture centres around the world. Generally the success of a pearl culture industry depends greatly on a high production of good quality pearls as a percentage of the total numbers produced.

Shirai (1970) has categorised the cultured pearls as follows:

Class A

Features: flawless, one flaw, small flaws, small stain marks, pink, silver or light cream in colouration. These pearls are further classified into:

A-1:	Top pearls-perfectly round, pink, flawless and lustrous. This class may also include pearls with small blemishes of the size of a pin point.
A-2:	First class pearls - with slightly larger pits and protuberances. When treated these pearls become indistinguishable from the pearls categorized as A-1.

Class B

Features: fairly large flaws, stain marks, creamy in colouration, and irregularities in the shape.

Class C

Features: wild shaped, badly coated, heavily marked, clayey lumps, half good and half bad. These pearls are usually referred to as ‘trash pearls’.

Generally, in a commercial pearl culture farm the combination of class A and class B pearls should account for at least 60 % of the gross production of cultured pearls for it to run economically. The remaining 40 % of class C pearls are usually rejected. However, their nuclei can be often salvaged and reprocessed

Review Questions:

Short answer questions:

        i.            Write the Biological name of Pearl Oyster.

      ii.            Write the Biological name of Bombay Duck.

    iii.            Write the Biological name of Lobster.

     iv.            Who is the father of pearl Industry of Japan?

       v.            Give any two important species of pearl oysters producing good quality of pearl.

Write Short notes on the following:

a)       Harvesting Methods of Bombay Duck.

b)      Harvesting Methods of Indian Mackerel

c)       Harvesting Methods of Pearl Oyster

d)      Formation of Pearl

Long answer questions:

1)      What is harvesting? Describe harvesting methods of Harpodon.

2)      What is harvesting? Describe harvesting methods of Mackerel.

3)      Describe the Harvesting Methods of Lobster.

4)      Describe the Harvesting Methods of Pearl Oyster

1.5 Crafts and gears in Indian Fishery

                                                        

(Contents - Crafts – Catamaran, Machwa, Dinghy, Dugout canoe, Built –up boat

Gears – Gill net, Dol net, Purse net, Rampani net, Cast net )

Introduction   

In India, a large variety of crafts (boats) have been designed for Inland fishing. The nets or gears and other devices for catching fishes are also numerous and ingenious. But both crafts and gears were invented centuries ago and  probably  have  remained  static and  have shown little or no  change or improvement in India,  unlike in  other  countries. This has hindered or restricted the exploitation of our inland waters. It   is only   in the last decade or two of 20thcentury that some attempts have been made to use motorboats and   modern steam vessels for the purpose. For the efficient management of fishing, it is imperative to know the type of fishing crafts and gears used in reservoirs.

            Various kinds of traditional crafts and gear, locally made, are in use since centuries for capturing different kinds of fishes including crustaceans. Some of these are used only for catching fishes, others for fish and prawns, while some are used for prawns, lobsters and crabs only. During the recent years, mechanized crafts and gear have been used for fishing.

5.1 FISHING CRAFTS

Fishing crafts are most essential for catching the fish in large scale water bodies. The types of fishing crafts of India falls under two general categories. These are non-mechanized and mechanized fishing crafts. The categories of fishing craft types comes under non-mechanized are dugout-canoes, plant built canoes, masula boat, built up boats. The mechanized crafts are line boats, trap boats, dol netter, gill-netter, trawlers. Some of the different kinds of fishing crafts used for fishing are mentioned below

5.1.1 Catamaran: -

        i.            Along the east coast, the simple craft used is called “Catamaran” (Tamil kattu =binding, maram=wood). Catamarans are traditional crafts used by fishermen of eastern coastal sides of India from Orissa to Kanyakumari. Later, its use was extended to Thiruvananthapuram and Kollam.

      ii.            Catamaran is a keel less craft formed by tying together few logs of lightwood with coir ropes. Two wooden supporters called Catamarans are used for lashing them together (Mathur, 1978).

    iii.            Catamarans are of two types, they are 2 feet and 1 .4 feet respectively. When the logs are tied together they become curved and shaped like a canoe.

     iv.            Catamarans are broadly of two types, the big one 7.50 to 8.50 meters long and 0.80 meters wide and the small one 4-5 meters long and 0. 60 meters wide (Korakandy, 1994). The former accommodates three to four fishermen as a unit and the latter is operated by one or two fishermen.

       v.            The investment required for a new catamaran is Rs. 10000 – 16000 varying upon its size'.

     vi.            A technical specialty of a catamaran is that it is a versatile craft and can be used almost all seasons at all points on the shore. Some types are operated with additional riggings like out-trigger booms and floats so as to ensure proper stability under varying loads.

Fig. 5.1Traditional Kattumaram catamaran upper,

There are four types of catamarans are known to be in use

a.       Andhra type: - It is 5-7 meter in length and made of heavy wood. Planks used in fitting the sides often include strong median logs and are known as wash boards.

b.       Boat catamaran: - It consists of three longs fitted into a regular boat shaped and is used on the coast around Mandapam and Mukkur areas. Wide variations of this type are found in the Tuticorin, Cape Comorin and Colachel areas.

c.       Coromandel type: - It is made up of 3-5 logs, with many variations in pattern. A specialized type is the seven logged catamaran or kolamaran used in flying fish fishery off Nagapatnam. It is most commonly used around Tamil Nadu.

d.      Orissa and Ganjam type: - It is boat shaped, made up of 3 to 5 logs of 20’to 25’. It is made up five logs, which are not tried together by rope; but are pegged with wood.

5.1.2          Machwa Boats

§   It is a modern motorized boat. It is mainly used in Bassein.

§   It has a broad hull, pointed bow and straight kill.

§   Country craft motorization was the first step in the introduction of mechanized fishing. Maharashtra was the first to introduce motorized boats in Indian fishing.

§   Some of the fishing boats motorized was the Satpati-type, Machwa and tuticorin type boat. Pablo boat was a new design introduced in motorized craft.

§   An important improvement in fishing was the introduction of larger boats and great efficiency in the speed of low and speed with the gear.

§   Satpati Boats are Medium sized fishing vessels around 12 to 14 meter long and 3 meters broad these are named after the Satpati Village in Maharashtra were they are manufactured in good numbers. Out of all the indigenous fishing vessels Satpatis are the most suitable for motorization and off-shore fishing due to their robust hull design. These are used on the west coast along the Bombay – Cambay coast and north of Ratnagiri.  

Fig. 5.2 Machwa Fishing boat (Saurashtra)

Fig.5.3 Satpati Boat (Maharashtra)

5.1.3          Dinghy and nauka: -

o       These are carvel boats of Orissa and West Bengal.

o       Naukas are well designed and constructed up to a size of 13m. X 3 m.x 2m.

o       Dinghi and naukas are quite spacious.

o       These are used for a variety of purposes including fishing operations.

Fig.5.4 Inner view of Dhingy

5.1.4 Dug-out Canoes

        i.            The dug-out canoes are made by scooping out the wood from a single log of mango or jungle jack. The keel portion is thicker than the sides. It is shaped by using teak panels if necessary.

      ii.            The dug-out canoes may be large or small. The large ones are 9.50 - 12.50 meters long, 0.90 - 1.50 meters wide and 0.75 - 0.90 42metres deep. The small ones are 7 .20 - 8.50 meters long 0.90 - 1 .20 meters wide and 0.45 - 0 .60 meters deep.

    iii.            Seven to eleven fishermen can work on large dub out canoes where as the smaller one can accommodate three to six fishermen.

     iv.            The investment requirement on bigger dug out canoes is high. A bigger dug-out canoe now costs Rs.30000-60000 depending up on the material used.

       v.            The dug-out canoes are used eight months in a year from October to May (Directorate of Fisheries, 1969).

     vi.            Dug-out canoes are modified into high board dug-out by adding planks stitched to the sides of the dug-outs.

   vii.            Mango (Mangifera indica) wood is mostly used for these canoes. The dug-out canoes (Shoe dhoni) of Andhra coast are made out of palm tree trunks.

     ix.            These are mainly used on the Kerala and Kanara coasts and also between Colachel and Kathiawar.

       x.            The large dug outs (Vanchi, Odams) from the main fishing crafts of Malabar Coast, operating a variety of nets. They are 10-12 m. long.

     xi.            The smaller dugouts known as Thonies are generally used for gill nets, drift fishing and for seining. These dug-out canoes are operated in large numbers from the sandy beach along the southwest coast of India.

   xii.            The dug - out canoes are employed for day to day fishing operations and they are hauled on shore when not in use.

Fig.5.5 Dugout canoes. Called Donga.

5.1.6          Built up boats: -

        i.            These are the best type of constructed, indigenous boats seen on the West coast, north of Ratnagiri and along the Bombay Camby coast.

      ii.            The Ratnagiri type has a pointed bow, straight but narrow keel and low gunwale.

    iii.            The Bassein type, locally called machus has a broad hull, pointed bow and straight keel.

     iv.            The Satpati type, popularly called galhat has a medium pointed bow broad beam, straight keel and high gunwale. The broach type is flat bottomed and used in inshore and estuarine waters.

       v.            The two extreme ends taper to a point with a round or a flat bottom. In the absence of a keel the bottom wood is distinctly left thicker than at the turn of the bilge and the sides. There are no additional strengtheners either longitudinal or transverse except for a few thawarts, which are used as cross benches. The use of metal fastenings is hardly seen, but coir ropes are used for the purposes of fastening.

     vi.            There are all exclusively sailing canoes, though oars, paddles and punting poles are also used. The sea going fishing canoes are usually in the length of 30-40 ft. and 3-4 ft. in width.

Fig.5.6 a carvel-built boat of Orissa

   vii.            The small dugout canoe with its sides built up to a greater height with wooden planks sewn together with coir ropes is the simplest form of a built up canoe.

 viii.            These types of built up canoes with out-trigger fixed to one side is commonly used in fishing along the Mysore coast.

Types-

a)       Coracle: - It is operated by 2-3 fishermen on river, canals and small reservoirs. It shape is like round basin and constructed from splitting of bamboo, its bottom and outer surface is covered by leather.

b)      Kakinada: - It is without keel. It is open type with little space decked. It is common for inshore fishery and can also be used for rivers, lakes and reservoirs.

c)       Shoe Dhonie: - It is operated by 3-4 persons for fishing with gill nets. It is about 8.5 to 9.5m in length and wide constructed from teakwood, it is carvel type and shape like shoes. Nails are used for its construction. It is used for fishing on seas and rivers, commonly used for fishing in river Godavari.

Rampani Boat:-

It is large in size with 15mx3m. It is used with rampani net for Mackerel fishing. It has narrow keel and more spread out planks. Smaller out trigger canoes are used in area between Bhatkal and Majali. Canoes with single out trigger are used on the Kanara and Kokan coastal area. It is also known as out trigger canoes.

Fig.5.7 Rampani boat

Musula boat: -

  i.            It is a non-rigid boat constructed with planks sewn together with coir rope, but without frames or ribs, so as to withstand the severe knocking of the surfs.

ii.            Masula boats are up to 9 m in length, although generally smaller. There are various patterns e.g. bar boat in Orissa and Padava on the Andhra coast. A variant with ribs inside has been developed in the area between Kakinada and Maslipatnam.

iii.            The Masula boat of the east coast is the simplest form of built up boat, peculiar in its construction with entirely stitched wooden planks for the hull with or without transverse frame insides.

iv.            The Tuticorin type of built up boat is a fast sailing lugger with a simple backbone assembly and hull planking firmly secured to the inside frames or natural crooks with iron or galvanized iron fastenings. The ‘Navas’ of Andhra coast are yet another type of built up boat popular on that coast.

 v.            ‘Batchary’ and ‘chhot’ types of fishing boats are from West Bengal mostly operating in the Hooghly estuary. 

vi.            The best type of built up boat for fishing are from Maharashtra and Gujarat coasts, where excellent hull forms are built to greater details out of best timbers teak (Tectona grandis) for the hull, Babul or Cutch (Acacia sp.) crooks for the frames and Poon (Callophyllum sp.) for the mast.

vii.            ‘Lodhias’,’Machuwas’, ‘Kotias’ and ‘Satpati-Varsova type’ of boats are some that have won great admiration from naval architects for their design and construction.

Fig.5.8 Chhot – side view, Orissa

Plank-built Boats

  i.         Plank-built canoes are constructed by seaming together planks of wood using coir ropes and copper nails (Bhushan, 1979). They are made with or without ribs on the sides.

ii.         Black pitch coating is used to make them water tight. These undecked crafts are also found in two sizes. The large ones measure 11-13 meters in length 1 - 1.5 meters in width and 0.70-0.80 meters in depth (Korakandy, 1994).

iii.         The small ones are 6 - 9.50 meters in length, about 0.90 meters in width and about 0.68 meters in depth. The large ones are operated by 12-15 fishermen while the small ones carry a crew of 4-6 persons.

iv.         The large ones are used from July to October. The smaller ones are used from September to March/April.

Fig.5.9 Plank-built, called "Dinghy/Jal dinghy

5.2 FISHING GEARS 

1. The word ‘fishing gear’ is synonymous for ‘fishing net’ which is used to catch the fish in the water bodies. Generally the fishing gears are categorized as active and passive gears. 
2. The passive gear needs knowledge of behavioral biology of the fish to be caught, as the fish has to enter the stationery gear voluntarily.
3. In the case of active gears, they are operated (either towed by boat or moved by hand) in the path of the fish concentration and general energy intensive, more productive than the passive gear.
4. Fishing gears are also referred as drift nets or set nets depending on whether the nets are moved in water or made to remain stationary in water.
5. Normally selection of a particular fishing gear (whether active or passive gear) is done according to the type of species caught in the fishing grounds.

5.2.1          Gill Net:

Gill net fishing is the primary method used by Indian people of the Klamath and Trinity rivers to catch salmon and steelhead.

Meaning and working principle:

a)       A gillnet catches fish that swim into it. It has a float line along the top and lead line along the bottom. The netting hangs straight up-and-down in the water like a good fence.

b)      A gillnet catches fish by their gills. It works like this: the twine of the netting is very thin, and either the fish does not see the net or the net is set so that it traps the fish. The meshes of the net hang wide open. When the fish swims up to the net it sticks its head right into one of the meshes.

c)       If the fish is too small for the mesh it will swim right through and get away. If the fish is too big for the mesh it might tear the net and get away. If the fish is the right size it pushes its head and body tightly into the mesh, but it is too big to fit through.

d)      When the fish tries to pull its head out of the mesh the thin twine cuts into its skin; its gills and fins get caught in the mesh. The fish stays in the net until you pull it up. Fish are also caught when the net wraps around them.

e)       Gillnets can be used in many ways. They can be made to rest on the bottom, to hang between the bottom and the surface, or to float on the surface. Gillnets can be set in one place with anchors, or allowed to drift with the current.

f)       The various names are given to gill nets for which type fishing it is used i.e., on the basis of type fish The gillnet used to catch mackerel is known as Ayila - Calavala, for seers, eel and catfish as Olukkuvala, for skates and rays as Thirandivala, for white baits as Nettolivala, for sharks as Sravuvala (Korakandy, 1994).  

Material Used:

1. The net is made of synthetic fiber which is woven to form long net webbing with specific knots at corners to give effect to mesh work. Formerly the net was made of cotton or hemp, but now the synthetic fiber replaced it. As the transparency of the net has effective role to play in the crossing attempt by the fish, it is necessary that the construction material of the net be transparent synthetic fiber. Various dyes are nowadays used to make the net invisible, when spread in water. As this net is generally used to catch big size fish, the material of the net is made strong enough to catch big sized fish.
2. As the transparency of the net has effective role to play in the crossing attempt by the fish, it is necessary that the construction material of the net be transparent synthetic fiber. Various dyes are nowadays used to make the net invisible, when spread in water. As this net is generally used to catch big size fish, the material of the net is made strong enough to catch big sized fish.
3. The mesh size varies with the size of the fish species to be caught.

Operation:

1. Gill nets are operated throughout the length of the river, unlike other gears, with more concentration in the lower reaches. It is operated during day and night throughout the season.
2. The nets, restricted to 100 feet in length, are placed in the river with corks and weights to allow them to hang in a vertical position.
3. Gill net is usually operated as drift or set anywhere in the water column by one or two fishermen from a canoe. Sometimes it is operated as encircling with the help of two canoes and 2-3 nets. After joining the nets they encircle an area. Then the fishermen enter inside the circle and splash water to scare the fishes and drive them into the net. Sometime they make noise by beating the sides of the canoes using poles.
4. Same method is used to capture fish hiding under large obstructions.
5. Set net is operated during the interface between tides and it is hauled back within 15 to 20 minutes. Otherwise they attach heavy stones- at bottom comers of the net to prevent drifting.
6. According to fishermen 50-60% of the catch is obtained from the coiled end. The central part of the net might be acting as leader line to drive the fish into the coiled ends. There are minor variations in the construction and operation of gill nets from place to place due to the difference in topography of the area, current, depth of water, target species and mode of operation. Fishermen often keep surface and bottom gill nets in their canoes and depending on the species availability and area they select the net.
7. A common practice is that the gill net is spread in the evening, given support of bamboo poles and the same is hauled up in the morning to collect the catches.

 viii.            The catches are generally bottom feeders including cyprinids of various kinds.

9. Kuppam River is often set in the form of an arc with both ends coiled inside.

Fig. 5.10 Gill net

Types: Three types of gill nets are in common use.

a)          Drift or Surface gill net.

b)         Anchored or Column gill net

c)          Staked or Bottom set gill net.

a) Floating or Drift or Surface Gill Net:  Floating or Drift gill nets are operated in the surface layers and drift with the current.            It is generally meant for entrapping surface feeders among carps. It comprises units of net webbing, floats, sinkers, head foot robes and anchors. The net is made of synthetic fiber, which is woven to form network. The size of mesh is kept as per size of the fish to be caught. A single unit of net, also known as 'shot' is usually 25-40 m long and 1.5-30 m deep. Several units of nets are joined together to form a very long surface gill net.

Fig. 5.11 Floating gill net

Fig. 5.12 Surface gill net- Chandi Jal- A Drift gill net – net of Waste Bengal

Two types of surface gill nets are in use – one is the set type and the other is the drift type. In the set type one end or both ends of the net are set by anchors. Alternately, heavy stones are tied with a long rope to the foot rope so that net gets straightened. Sinkers on the foot rope so that net gets straightened. Sinkers on the foot rope and floats on the head line enable the net to remain spread somewhat straight like a wall. During operation in river or reservoir, fishes, on attempting to cross the net are entangled by galling in the mesh network. This net is operational throughout the year. The fishes caught are generally surface feeders such as some major carps.

b) Anchored or Column Gill Net

            The basic form of this net resembles the surface gill net. The length of the float rope is however, kept such that the net remains suspended in mid column of water. This net is operational in deep water. In the early morning, the net is carried to the deep area of river or water tank or reservoir and lowered form a boat skillfully so that the net gets spread in full length. The anchoring is done after it gets straightened (bow shaped). The floats on the head rope and sinkers on the foot rope enable net to stand as a wall. The bigger floats on the surface of water, attached to additional sinkers through the net help additionally for straightening the net. The catches are generally major carps.

c) Staked or Bottom-set Gill Net:

            Bottom set long lines are operated close to bottom for predatory demersal fishes such as sharks, sea breams, sea bass, groupers, snapper, etc. Main line is positioned at an appropriate height from the bottom by adjusting buoyancy. As the main line does not touch the ground, the gear is particularly suitable for uneven grounds inhabited by high value perches.

Fig.5.13 Bottom Gill net

           

5.2.2    Dol or Bag Net –

        i.            This net is extensively used in Maharashtra and Gujarat.

      ii.            Operation: The Dol is operated in depths varying from about 15 to 50 meters. The operation is carried out at greater depths as the season advances.

    iii.            The net is tied either to stout wooden poles or thick ropes anchored with heavy stones which face the tidal flow.

     iv.            It has mesh size of about 200 mm at the mouth portion. This is gradually reduced to 10 mm (Knot to Knot) at the cod end, as shown in figure.

       v.            During operation it resembles with a fixed bag net and generally the Bombay duck gets entrapped in large numbers.

     vi.            Various modifications of bag nets are in use, but the dol, a bag net of Bombay coast, is more popular.

Fig. 5.14 Dol net: a bag net used for fishinng of Bombay Duck

Fig. 5.15 Mada Valia – A shore – Seine of Coromondal coast.

Dragnet: In the netting process the nylon net also known called as Drag net is used. Through the top meshes of net run a thick and strong cord which was held at either ends by a number of fisherman. This drag net was pulled with the help of rope and slowly – slowly the most part of the drag net was pulled out by the workers at corners of the pond. In such a way the big drag net become modified in to the pouch net or bag net. In this bag net, all the fishers were collected in the small area.

5.2.3          Purse Net

This is purse shaped net, operational from a boat. It is generally used in Ganga rive system for catching hilsa fish. Two types of purse nets are in use. : (a) Kharki Jal and (b) Shangla jal. Some basic features of these purse nets are given ahead.

(a)    Kharki Jal: 

              i.         It is a kind of purse net, rectangular in shape, has two lips made of split bamboo, which are hinged at an angle. In the middle of the lower lip, a pole or bamboo stick is attached.

            ii.         There is ring in the middle of the upper lip through which a bamboo pole passes down to the lower lip as shown in the figure.

          iii.         Operation: The fisherman, standing on the boat, presses the pole to keep the mouth open when the fish (generally hilsa) enters the jal.

           iv.         The pressure is released soon afterwards and the mouth closes resultantly. As hilsa in shoal ascends the rivers during flood time, the net is brought in use with the aim of catching this fish.

(b)    Shangla Jal:

              i.      This also is a purse shaped net, resembling kharki jal in construction, but the length of the bag is 10 ft. and the semi-circular mouth is supported by 20 ft. long bamboo stick.

            ii.      In the middle of outer lip there is a cord attached firmly to the lip.

          iii.      In this net, the vertical bamboo pole is replaced by the weighted cord for opening and closing the mouth.

           iv.      Operation: Because of complex nature of construction of this net, its operation is not easy. The net is set at any desired depth of water to each the fish, which is generally hilsa.

             v.      The fisherman makes standing position on a boat or raft and manipulates skillfully to keep the mouth of the shangla jal fully open. During operation, as soon as the fish reaches the net, the cord is stretched. This results in the catch of the fish in the net.

                      Fig.5.16 Shanglo Jal – A Purse net

5.2.4    Rampani Net (Shore Seines)

(i)     ‘Rampani’ is a type of net or rather a unique method used for shoreline fishing. The large net of the karwar coast is called, “Rampani net”.

(ii)   A single net can be four thousand to five thousand feet long

(iii) These are large sized nets made up 100-500 rectangular pieces, Joined end to end. Each piece may be 3-6m long. The side pieces are of larger mesh of 3-5 cm, but the middle pieces have meshes of smaller size (1-2cm).

(iv)  Operation: Floats are fixed to the upper rope, and sinkers are provided to the lower rope. Long ropes are attached to both the ends for hauling. One end of the net is held on the shore by 20-25men and the net is carried on boats. It is laid into the water in a semicircular manner to enclose large area around the fish shoals, bringing the other end back to the shore, where it is held by a second group of 20-25 men. The two ends are pulled and the net is dragged to the shore.

Fig. 5.17 Rampani net

5.2.5 Cast Net

a)       The cast net is most commonly used in rivers or ponds Uttar Pradesh, Bihar, West Bengal and Orissa consists of conical netting and a hand rope, as shown in figure.

b)      The netting is made of nylon twine (formerly of cotton) which is skillfully woven to form meshwork.

c)       The mesh size varies from 1 to 5 cm. (in descending order from the conical end) and the depth is between 2 to 5 m. Sinkers in the form of iron rings are attached around the skirt. The hand rope is of cotton or nylon, 5-8 mm in diameter and 7-15 m. in length. Generally the weight of the net is between 4.5 to 7 kg.

d)      Operation: The net is cast into the water from the margin of the tank or pond or from a boat or stakes made of bamboo or wood in such a way that a group of fishes get covered over by the net and, thus entrapped. The hand rope is carefully pulled to close the spread skirt. The overall result of operation is such that the fishes are caught in the pocket of the net. Its operation is always in shallow water areas devoid of weeds and submerged obstructions of any sort. The fishing operation can be done all the year round. All type of fishes from surface feeders to bottom feeders get entrapped and brought to land.

Fig. 5.18 a common cast net in two conditions: (i) Spread / cast form, (ii) Straight/hanging form (s)

Review Questions

Define crafts and gear. Describe any two type’s crafts and gear used in Indian fishery.

Define gill net. Give the meaning, working principle and operation of Gill net.

What is catamaran? Give an account of catamaran.

Describe in detail various types of fishing crafts used in Indian fishery.

Describe in detail various types of fishing gears used in Indian Fishery.

Describe the net used for fishing of Bombay duck.

Write short notes on:

i)                                                                              Fishing crafts,

ii)                                                                            Fishing gears,

iii)                                                                           Catamaran,

iv)                                                                          Dinghi, 

v)                                                                            Built up boat,

vi)                                                                          Dugout canoes,

vii)                                                                          Dol net, 

viii)                                                                       Cast net,

ix)                                                                          Purse net,

x)                                                                            Gill net, 

xi)                                                                          Rampani net

******

1.6Fishery byproducts                                                                                 

        

(Contents: Fish meal, Fish flour, Liver oil, Isinglass, Fish glue, Fish manure, Fish fin soup)

Introduction

Fishes that are consumable for human consumption and discarded parts of fish as gut, gills, fins, etc. may be processed into edible meals and oils that are obtained as by-products of fish industry. Several products are obtained from the wastes of fisheries; they include the fish meal used for animal feeding and as the manure, the fish flour for human consumption, leather, and glue form fish skins, imitation pearls, foam producing compound for extinguishers and active carbon form scales, isinglass and adhesives from air bladder, insulin from pancreas, sex hormones from gonads, protamines from milt, histamine from flesh and guanine and cytosine from scales. The details of various fish products and their uses are giving ahead.

a)      Fish Meal        

Meaning: It is the dried fish powder from which oil has been extracted. It is the residual cake after oil extraction. Fish meal is a nutritious feed supplement mainly or proteins, minerals, and vitamins.

Process: Trash fishes like Leognathus, lesser sardines and anchovies, and fish waste are commonly used for the production of fish meal through wet reduction process. The basic principle involved is that the source materials are ground and boiled in sufficient quantity of water in large pots. The result is that coagulation of protein occurs, and it is followed by release of water and oil.

Then water and oil are separated. The liquid protein, known as press liquor, is passed through a screen made of canvas or coir bags in screen places to remove water and separate the solid particles of fish. Later, these particles are returned to the press cake. After drying the press cake in the sun, it is ground well and then packed in polyethylene-lined gunny bags.

In dry process, the raw material is exposed in high temperature (in sun), or more commonly in steam jacketed drums, often under partial vacuum. The vacuum drying process gives a superior product.

            The solid mass obtained, is packed and marketed. The fish meal can be stored in air tight sterilized containers for a fairly long period.

Composition:  The constituents of the Fish meal includes –

i)        Proteins 65%,

ii)      Moisture, fat and ash contents vary at 6-10%, 5-10%, and 12-33% respectively,

iii)    All essential and non-essential amino acids,

iv)    Minerals such as calcium, phosphorus, copper, zinc, manganese, iodine and selenium.

Use: It forms a very valuable food for poultry and cattle. Due to its high protein and vitamin contents, it increases milk and egg production. It is demand by fish feed manufactures as well as for the reason of its very rich nutritive value.

b)      Fish Flour (Hydrolyzed protein) :

Meaning: This is very superior quality of fish meal which is used for human consumption.

Process: It is prepared on a commercial scale mostly by the application of solvent extraction process. The fish flour, prepared thus, forms an ideal protein supplement to human diets.

Composition: Protein

Use: It can be used in several forms, but the best use (also an easy use) is its blending with wheat or maize flour (Moorajan and Lahiry, 1962; Moorjan et.al., 1965). It is also added in small quantities for enriching the nutritive value of bread, biscuits, cakes, sweets, soap and gravel. It has been found that mixing of fish flour at level up to 10% does not alter the taste and the overall appearance of breed is rather, better. It is a favoured item in Africa and South-East Asian countries.

Fig. 6.1 Preparation of fish Sausage: A-An eviscerated form of small sized fish:

B - meat after separation; C- Collected skin, bones, fins etc.

c)       Liver oil

Meaning: Oil produced from liver of fishes like Cod, Tuna, Halibut and some of the Sharks are called liver oil.

Fishes used: Three classes of fish livers of commercial values are recognizable.

(i)   Fish livers with high oil content and low vitamin A potency. They include cods whose liver yields 60-75% oil with 500-20,000 i.u/g vita.

(ii)  Fish livers with low oil content and high vitamin A potency: They include Tuna, whose liver yields 4-28% oil with vitamin A potencies of 25,000-600,000 i.u/g.

(iii) Fish liver with high oil content vita. A. They include fishes like hammer headed sharks, the liver of which yields 25-75% oil with vitamin A (potency of 300,000 i.u/g). The extraction of oil from liver is done by the methods given below.

Composition: Fish liver oils contain several valuable items including 55-75% fat, 5-10 % protein, water and vitamin A and vitamin D. The two important vitamins, vitamin A and D, are essential for man, are present in liver oil in a required quantity. As such, the medicinal value of fish liver oils is enormous.

Process: The various firms use various methods for extracting the liver oil. Following are some common methods:

(i)                 Boiling method: Liver is chopped into small process and boiled with sufficient water. Then the oil is skimmed off from the surface of water. This is the simplest and cheapest method of extraction of oil from liver. There is use of two metallic receptacles with 2-3 inches of space between them. Liver pieces are placed in the inner chamber and water in the space between the two receptacles. Water is heated to boiling point on fire. In this duration, liver is constantly stirred to avoid oxidation.

(ii)               Steaming method: The liver pieces are heated by steam under pressure using steam kettle with automatic safety valve to control pressure. In the kettle is fitted a stirring mechanism-operated steam. In modern oil extracting plant, which represents the adaptation of recently developed technology, liver is sent in the form of a continuous steam to a cooker, which is proved with a rotating steam element for heating. The temperature is gradually raised to 90-97⁰C and the liver is allowed to pass though on shaking sieve to a settling tank. The oil is drained through a pipe and liver residues diverted to a centrifuge for further processing.

(iii)             Solvent extraction method: Liver pieces are first crushed to a pump and dehydrated with salt like sodium sulphate to remove moisture. The dehydrated mass is extracted from an organic solvent like ethylene-dichloride oil, obtained by distilling solvent like ethylene- dichloride oil, obtained by distilling the solvent. As it is a costly process, it is less preferred.

(iv)              Alkali method: Liver pieces are first allowed to be digested in a weak alkali solution by heating. The hot liquor is then centrifuged to release oil (Sen and Chlubhaiah, 1968).

The stock of extracted oil is sent for purification, then standardization for check and correction of quality and finally propelled in the trade line for marketing. The main centers of shark liver oil industry in India are located at Kozikode, Travancore and Mumbai.

Use: As the oil has great medicinal value, particularly in curing both ‘rickets’ and ‘Xeropthalmia’, it has great demand in the country.

d)      Isinglass:

Meaning: Isinglass is a pure gelatinous substance obtained from the inner lining of the swim bladder (air-bladders) of fishes like catfish, carps, eels, polynemids, sciaenoids, sea bass, etc. It is a high grade collagen product.

 Process: It is made in various parts of the world form the swim bladders of 'sounds' as they are known to the trade of such diverse fishes as the Sturgeons, Carps, Cat-fishes, Cod, Ling, Hake, Squeteagues, Drums, and Thread Fins.

From the fish selected, the bladders are first removed and the blood and adhering materials are scraped off. After that they are cut open and washed thoroughly in running water. Following this action, the outer black membrane is removed by scrapping and the bladders are cut into pieces. The pieces are dried in an artificial drier or in open sky, i.e. given sun exposure. After all these processing, the product (Isinglass) is stored in suitable containers.

Use: There are many uses of this product. The most common use is in clarifying beverages like bear, wine and vinegar; for making jellies, etc. and in the preparation of certain cements.  Isinglass is also effective in the reduction of the suspended solids in beer and increase rate of filtration form 3,000 to 11,000 liters. Other uses of this product are as an adhesive base in confectionary products, Indian ink-work manufacture and also as an efficient adhesive for glass, pottery and leather products manufacture. Nevertheless, isinglass products having moisture content less than 8% find preference for industrial purposes.

e)       Fish glue

Meaning: Fish glue is a product obtained mainly from such fishes as the Cod, Haddock, Pollack and Hake. 

Process: Most of it is derived from the skin of the fish, but waste glue and fish-head glue are also manufactured.

Use: Fish glue is considered a good adhesive, and is used for smearing the backs of glued stamps and labels. The glue obtained from cod is of superior quality and finds use in photo- engraving. When the product is of low quality it is utilized as adhesive for paper boxes, shoes and other things such as furniture where joining is required. U.S.A. is known for producing larger amounts of fish glue.

f)       Fish Manure-

Meaning: Fish manure is inferior quality of fish meal which is unfit as animal feed.

Composition: It contains 5-7% nitrogen, 4-6% P2O5 and 4-6% CaO. The fish, which are generally used for preparation of fish manure, are sand-horse mackerels, mackerels, sardines and a few other species. They are available in abundance in the coastal fishing areas.

Process: Preparation of fish manure is simply by drying fish in the sun on the sea beach. The supply of fish is maintained in two ways: when there is abundant supply of fish and surplus are left after sale, they are used in sun drying. Also when the fish are brought to the shore in spoiled condition and are found unfit for human consumption, they find utility in the form of dry fish. The fish are simply spread on the beach and dried. This dried fish, on mixing with ash forms an ideal kind of manure. The product being already cooked during the processing for oil extraction decomposes quickly in the soil and mixes well.

Use: It has high nutritive value. Generally three kinds of manures are obtained from fish: fish manure, prawn manure and fish guano. It is used largely as manure in the plantation of coffee, tea and tobacco.

Fish Guano: It is also known as fish cake. It is a separate kind of fish fertilizer. It is the fish cake left after the extraction of oil. Guano is produced as byproduct from the oil extracting fishes. It is rich in protein and nitrogen contents along with Phosphorus and Calcium.

g)      Fish  Fin Soup-

Shark fins are used for making soup. There are two main grades of shark fins; one is fine one, obtained from small sharks, and the other is the coarse one which is prepared for big sized sharks. They are first soaked in plain water or softened in water acidified with vinegar (acetic acid) with pH 2.5 to 5 for 2-3 days. Freshly cut fins require less soaking time. The softened fins are then treated with 10% acetic acid at 60⁰C for about one hour. The translucent cartilaginous rods which remain embedded in the fins of shark become visible. After removing skin, extraneous muscle, cartilage bones, etc. fins are boiled till the fin rays got separated from the remaining cartilage bones and muscle. The rays are separated manually, washed well, then soaked in cold water, containing small quantity of hydrogen peroxide for 2 hours and then washed. The fine product can be used immediately for the preparation of shark fin soup. The softened clean fin rays, after separation of extraneous materials can be washed well and dried in the sun. The dried rays, which usually contain moisture for 5-8% level only, can be stored in polythene bags marketed foreign countries like China, Philippines, Hongkong, Singapore etc. Fin soup is favoured by Chinese and costs about US $ 110 dollars in Hongkong restaurants.  

Fish food as medicine: e.g. Mackerel

The dosage: 2-3 servings a day (30g)

The target: Achy back, joints, neck

It's not a mystery that omega 3 fatty acids have a major role to play in maintaining overall health. Consuming fish rich in this essential nutrient and low in mercury, such as mackerel and tuna can help relieve back pain and boost mood, studies say.

Typically, the blood vessels at the edge of a spinal disc are responsible for the transfer of nutrients. A diminishing blood flow will then cause the spinal discs to lose their function and degenerate. Omega 3 fatty acids ensure that the blood reaches these spinal discs by reducing inflammation and tamping down blood vessels and nerves in that area.

Vegetarians should get their daily dose of omega 3 fatty acids from dried fruits like walnuts and flaxseeds.

Review Questions:

Define/Explain the following terms.

a)       Fish Meal

b)      Fish Liver oil

c)       Fish Manure

d)      Fish Glue

e)       Fish Flour

f)       Isinglass.

g)      Fish Guano

Write short notes on the following:

        i.            Fish Meal

      ii.            Fish Liver oil

    iii.            Fish Manure

     iv.            Fish Glue

       v.            Fish Flour

     vi.            Isinglass.

Short answer questions:

a.       What is the importance of Fish Flour?

b.       What is the importance of Fish Meal?

c.       What is the importance of Fish Liver oil?

d.       What is the importance of Isinglass?

e.       What is the importance of Fish Manure?

f.        Enlist methods of Fish liver oil Extraction.

g.       Give the composition of fish food.

Long Answer questions:

1.       Describe various Fish products in detail.

2.       What is liver oil? Give the composition, uses and process of extraction of Liver oil

****** 

1.7 Fish preservation techniques

                                                                 

                 (Contents: Chilling, Freezing, Salting, Drying, Canning )

Introduction

Fish, an excellent food for mankind is more easily perishable commodity and is spoiled preserved. To prevent spoilage of fish, some form of preservation is necessary. Preservation means, keeping the fish after it has landed in a condition whole some and fit for human consumption for a short period or for a longer period of over a few months. The methods used for the preservation of flesh, includes conservation by cold and also salting, drying, smoking, canning etc. The product obtained by drying, salting and smoking is popularly known as cured fish.

Causes of fish spoilage

The main components of fish are water, protein and fat. The spoilage of fish is a complicated process brought about by actions of enzymes, bacteria and chemical constituents. The spoilage process starts immediately after the death of fish. The process involves three stages:

1.          Rigor mortis

2.          Autolysis

3.          Bacterial invasion and putrefaction

1.          Enzymatic action: The Rigor mortis is a physical effect on the muscle tissue of fish caused by chemical changes following the death. In live fish, its movements are controlled by chemical signals which cause the eythmic contraction (stiffing) and relaxation of the muscles. This produces swimming action. After the death, the normal circulatory system breaks down and chemical signals leak into the muscle causing them to stiffen. This process is known as Rigor Mortis. In other words, in live fish the glycogen present in the muscle is converted to carbon dioxide and water after supply of oxygen to the cells. The blood circulation stops after the death of fish and the supply of oxygen is prevented. The enzymes present in the muscle convert glycogen into lactic acid. The pH of the fish muscle falls. The formation of the lactic acid continues till the supply of glycogen is completely used up.

After the completion of rigor mortis, muscle stiffness gradually decreases accompanied by increase in pH, ending up in softening of muscle. This is followed by breakdown of proteins by enzymes. This process is called as autolysis.

Thus autolysis can be described as an internal breakdown of the structure of the protein and fats due to a complex series of reactions by enzymes. Autolysis of protein starts immediately after rigor and creates favorable conditions for the growth of bacteria.

Enzymatic action is due to action of various enzymes found in the body tissue cells of fishes. They spoil the tissue by the process of autolysis and make the fish susceptible to bacterial attack. Protease for example can digest muscle proteins of the fish, catalose the gill spoilage and ATPase brings about ATP from muscle tissue in 6to 8 hours. Autolysis of proteins results in formation of amino acids and other nitrogenous products; which on further decomposition produce ammonia, carbon dioxide, volatile basic compounds and foul smelling products.

2.          Microbial action involves bacterial decomposition of the fish flesh. These bacteria are found in the lower part of the gastro-intestinal tract and on the general body surface of fish body.

The fish flesh having a PH 6-7 in living condition, provides a most suitable place for their growth and multiplication, proteins, constituting its 70-90% are degraded by proteolytic organisms such as Pseudomonas, Proteus, Chromobacterium, Holobacterium and Micrococcus etc. The carbohydrates present in a small amount in the fish flesh are spoiled by carbohydrate fermenting organisms like the Streptococcus, Leuconostoc and Micrococcus etc. Fats consituting5.3% of the flesh are digested by relatively few gram negative bacteria. 

3.       The chemical action involves oxidation: Rancidity is a more widely-used term for oxidation. It occurs when oxygen in the air reacts with oil or fat in the flesh of the fish. This leads to a sour or stale, unpleasant smell or taste. Oxidation is more pronounced in fat fishes for example, oil sardine, catla, trout and grass carp etc. Which as a result become decolorized? The oil starts getting oxidized as soon as it comes in contact with the atmospheric air. The colour of the fat and its viscosity changes and the fish becomes strong in taste.

Principles of fish preservation techniques:

Bacteria and enzymes like ambient temperatures and need to operate in the presence of water. They do not like low temperatures, or very high temperatures. They do not like to work in dry conditions. Many processing procedures in fact create the conditions that bacteria and enzymes do not like. Fish preservation methods (Chilling, Freezing, Salting, Drying, Smoking and Canning) are based on following principles.

1. Lowering the temperature:

Chilling food in the refrigerator or with ice slows down the destructive processes of enzymes and bacteria. The shelf-life of food can therefore be extended by many days. If we lower the temperature further, as in freezing, much longer storage times of many months are possible because all bacterial action and virtually all enzymatic actions is stopped.

2. Raising the temperature:

High temperatures kill bacteria and destroy enzymes. Processes such as cooking (boiling, frying, baking, etc.), hot smoking, canning, pasteurizing and so on extend the keeping time of the food.

3. Drying or dehydration:

Removing water from the food by drying it in some way is an effective method of stopping bacteria and enzymes from spoiling food. Drying can take place under the sun and wind (natural drying) or in a mechanical drier. Salting helps the drying process too, as it binds the water, making it unavailable to bacteria. Some high-temperature processing such as hot smoking uses a combination of drying and high temperatures to control bacteria and enzymes.

To stop oxidation of fatty fish we must protect the product so that oxygen in the air cannot reach the product. The simplest way to do this is to pack the fish in plastic bags that do not allow air to pass through.

Uses of fish preservation- (Chemical Methods)

A number of drugs and chemicals are effective in preventing spoilage of fish. Some popular ones for industrial uses are mentioned below”

1. Ascorbic acid prevents rancidity infant fishes.
2. Chemical ice i.e. ice concentration of sodium nitrite, may enhance keeping period of fish at this temperature by a week over the period achieved with ordinary ice.
3. Auremycin an antibiotic is very effective in preventing fish spoilage. This antibiotic is effective even at low concentration and nearly 50% of this antibiotic is destroyed during cooking.
4. Phenolic components of smoke viz. guaicol, cresol, pyrogallol, and catechol form certain wood have antiseptic properties and are thus helpful in preventing fish spoilage. These are particularly bactericidal, resulting in heavy kill off in the bacterial load of fish.
5. Acetic acid is a powerful preservative.
6. Detergent like sodium ricinole at in concentration of 0.2%-0.5% can destroy such bacteria as thrive in high salt concentration.

1.7 METHODS OF PRESERVATION

There are various methods of fish preservation; many of them are of local importance only.

Preservation can be done, both for short and long duration:

Preservation for short duration

1.7.1    Chilling (with ice)

Meaning: Chilling is a means of short term preservation of seafoods achieved by the reduction in temperature using ice. It is the preservation of the fish at 0⁰C to prevent the spoilage for short time. It is the most effective method of preventing putrefaction and extending the life of fish.

Principle: Here autolytic enzymic activities are checked by lowering the temperature.

Technique: This is obtained by covering the fish with layers of ice and temperature is lowered / maintained to about 0⁰C. However, ice alone is not effective for long preservation, because melting water brings about a sort of leaching of valuable flesh contents which are responsible for the flavour. Chilled fishes must be stored properly at constant temperature.

Merits: Ice is effective for short term preservation such as is needed to transport landed fish to nearby markets or to canning factories, etc.

Demerits: Icing and chilling can maintain fish fresh only for a very limited period. Quality deterioration takes place in chilled fish.

Preservation for long time

When the preservation is required for a long period of time, the fishes are passed through the cleaning, gutting and conservation and storage.

Cleaning:

During cleaning, the caught first are fish washed thoroughly in cold, clean water to remove bacteria, slime, blood, faeces, and mud, etc. from the body surface of the fish. It is being done under proper sanitary conditions.

Gutting:

After cleaning, the fishes are cut along their mid ventral side, and their visceral organs are removed. By removing viscera, the bacteria in the gastro intestinal tract and enzymes of visceral organs are removed along with it to prevent bacterial decomposition and enzymic autolysis respectively.

Conservation and storage:

Conservation is necessary to keep the dead fish in fresh condition for quite a long time. This is achieved by employing any one of the methods like freezing, drying, salting, smoking and canning.

1.7.2    Freezing/ Icing

Meaning: Freezing means removal of heat from the body. Freezing is a method low temperature preservation of fish that can ensure very long shelf life and can also provide a processed product very much similar to fresh fish.

Principle: Main principle behind this method is cool temperature do not favors the all activities of microorganism and also its enzymatic activity becomes inactivates, due to low temperature. To check the enzyme, bacterial action and putrefaction it is preferred to store the fish under lower temperatures. Freezing is achieved either by using mixture of ice salt or refrigeration.

Technique: Icing is done in 1:1 ratio, means one layer ice and one layer fish and so on. So that it does not make contact in other fish and also the weight should not be increased so much to lower side of fish. It is done in a plastic caret of about 40 Kg of its capacity.

The sub-zero temperature so obtained keeps the fish frozen throughout. During air freezing, water of the flesh separates and forms ice crystals, thus the quality of the fish is inferior. Frozen fishes are dipped in cold water stored at 10⁰ F; Freezing in brine is a rapid process and produces better quality of fish which retains its natural appearance. In fast frozen fish, only small sized ice crystals are formed which do not damage the tissues. Freezing of fish can also be accomplished with the help of a current of cold air. In brine, freezing, fishes are dipped in cold liquid.

To prevent rancidity the frozen fish is subjected to glazing with water or wrapped in a cover of moisture proof wax paper or cello phone. Glazing is dipping the frozen fish in water so that finally a layer of hard ice surrounds the fish. This layer affords protection against exposure of fish fat to atmospheric oxygen, thus preventing rancidity. Refrigeration need organization and initial for is establishment.

Merit: Freezing is more effective than chilling. It is the only method of preservation that preserves the fish for long period during transportation.

Demerit: Preservation by freezing often causes loss of flavour and damages the tissue. Most methods of long term preservation bring about major changes in the physical, chemical, textural and or ganoleptic characteristic of fish.

Types:

Deep freezing or quick freezing: When fish is intended to be stored for a long period, quick freezing is preferred which inhibits bacterial action. Deep freezing or quick freezing requires rapid lowering of temperature, say reaching -40⁰C in just half an hour. Because of this the zone of crystal formation of ice-31⁰C to 25⁰F (-0.5⁰ C to-3.8⁰C) is passed in a very short time preventing formation of larger crystals which damage the tissues. During quick freezing every part of the product comes within the range of 0⁰ to -5⁰C. Properly frozen fish at -20⁰C retains its physical properties and nutritive values for a year or more and is almost as good as fresh fish. Smaller sized crystals, shorter time taken for freezing less time allowed for diffusion of salts and evaporation of water and prevention of decomposition are some of the advantages in quick freezing. It has the advantage of preventing preservation for long time. It is done by air/gas freezing by brine or by metal freezing utilizing friged air/gas liquid or metal before freezing, the fishes are washed and the heads of large fishes are removed. In deep freezing bacterial action is inhibited. The fish retains its physical properties and nutritive value for several months.

There are three ways effecting quick freezing:

a) Direct immersion of fish in the refrigerating medium

b) Indirect contact with the refrigerant through plates

c) Forced convection of refrigerated air directed at heat transfer surfaces.

Cold storage preservation is practiced only at limited places in India. In Mumbai and Kolkata also little cold storage facilities are available. Fishes are kept overnight in the cold storage and then they are sent for marketing the next day.

Oil sardines, mackerel and seer are the three commercial important food fishes used in the application of refrigerated sea water for preservation. These fishes were stored in artificial sea waters prepared by dissolving common salt to give sodium chloride content 3.5% at a temperature of -1.1 to 0⁰C. In general the fishes stored in refrigerated sea water had firmer texture and better appearance than ice-stored ones. The oil sardines stored up to 2 days did not show any difference compared to ice samples. Further storing resulted inferior quality of the fish. Similarly mackerel and seer could be stored for 4 to 6 days and 12 to 14 days respectively.

Fig.7.1 freezing with ice

Freeze drying: This is a modification of deep freezing completely eliminating all chances of denaturation. The deep frozen fish at-20⁰C is then dried by direct sublimation of ice to water vapour without any melting into liquid water. This is achieved by exposing the frozen fish to 140⁰C in a vacuum chamber of freezing chamber. The dried fish is packed or canned in air conditioned room. Any loss of flesh contents by way of leaching during melting of ice is thus avoided. The product so obtained look fresh, retains its flavor, colour and quality.

1.7.3    Salting/salt curing

Meaning: Salting is a process where the common salt, sodium chloride, is used as a preservative which penetrates the tissues, thus checks the bacterial growth and inactivates the enzymes. This is one of the oldest methods for fish preservation.

Principle: Main concept regarding this techniques, is when the some amount of salt solution is entered into the fish flesh, it can delay the activity of microorganism or even inactivate them by reducing the water activity by process called “exosmosis” this forms the basis of the salting preservation.

Concentration of salt at 4-10% level in fish flesh is known to prevent the action of most spoilage bacteria as well as autolytic decomposition. When the concentration of salt is 20% or more in flesh, the decomposition process in the fish proceeds only very slowly.

Salt is a valuable agent in helping to prevent spoilage. Salt preserves by extracting water. This is called dehydration (drying), and happens because water from inside the fish is drawn out into the strong salt solution outside the fish. As the water moves out, the salt moves in, penetrating deep into the flesh of the fish. Water is essential for bacteria (germs) to grow, so if the water is removed, bacteria cannot grow. Furthermore, the spoilage bacteria do not like salty conditions. The more salt in the fish, the more they dislike it.

Technique: During the process the small fishes are directly salted without being cleaned. In the medium and large sized fish the head and viscera are removed and longitudinal cuts are made with the help of knives in the fleshy area of the body. Then the fish is washed and filled with salt for uniform penetration through flesh. Large fishes like sharks are cut into convenient sized pieces.

During salting partial dehydration of fish by osmosis also takes place. For salting, the temperature should be around16⁰C but for strong salting, normal atmospheric conditions are quite suitable. Salting commences as soon as the fish surface of the fish comes in contact with common salt and the end product shall have the required salinity with taste and odour.

The salt used should be pure common salt so as to keep the quality of the fresh fish. Traces of calcium and magnesium caused whitening and stiffening of the flesh and gives bitter or acid flavor to the product. In addition it does not allow the easy penetration of common salt.

Some of the factors involved in salting of fish which play an important role are purity of salt, quantify of salt used, method of salting and weather conditions like temperature, etc.

Generally, sardines, mackerels, seer fishes, cat fishes, sharks and prawns are used for salting.

Merits: Useful for long duration as compared to chilling and freezing.

Demerits: Stiffening and whiting to flesh may give bitter taste.

Types: Dry salting, cold salting, and wet salting are the methods employed in salting of fish.

a)       Dry salting (or Kench curing)

In this method the fish is salted, but the juices and brine (pickle) are allowed to drain away. For 2 parts of fish, you need 1 part of salt. Layers of fish are separated by layers of salt (alternate layers of salt) and placed into a wooden box that has slats cut out of the sides, enabling the draining of juice. It is important to layer the fish with the first layer being flesh-side upwards, and the next layer of fish being flesh-side down. The final layer should be salt. The box has a lid placed on top of the stack and weighted to press the fish down. This encourages faster salt penetration and water removal. Alternatively, fish can be layered with salt in a woven basket, with the pickle draining through the holes between the woven materials. The fish should be restacked, or re-packed, every 24 hours, so that the fish previously on top now end up on the bottom. More salt should be added as required. This is done to provide uniform salting and pressure which helps squeeze water out of the fish. Salting time varies from three days to a week, depending on the type and size of fish.

After a few days they are removed from the container and dried in the sun. Dry salted fishes are not relished much but they are less costly because their preservation is inexpensive.

Another way of dry salting is to fill salt in the abdominal cavity, after the process of guttation. The fishes are made to roll in salts over and over several time and then stacked between the layers of the salt. After salting, drying is done by the usual method in the dry and cool shady places.

b)      Cold salting

This method is done by spreading salt and crushed ice on the fish. About 22 to 26 lb of salt per ton kg of fish is usually recommended. After salting, the conservation is done in a room having a temperature range of 2-3⁰C. Salt may also have impurities in the form of magnesium and the calcium salts. These affect the taste of the fish and also decompose the flesh proteins. Impurities of such kind must be removed or the pure salt should only be used to retain the taste of the fresh fish.

c)       Wet salting

The principle of wet salting is to keep the fish for a long time in a solution of salt and water, otherwise known as ‘brine’.

In this method, the fish is splinted, gutted and cleaned as dry salting. One kg of salt is required for every three kg of fish, half the quantity of salt is rubbed on the cut surface of the fish. On the first day they are stacked on the floor of the curing shed to a height of 1-2 meters. Second day, half of the remaining salt is rubbed in and the fishes are stacked so that the top fish become the bottom one. On third day the remaining salt is applied and the fishes are stacked again. They are allowed to remain in this condition for another eight days and then removed. They are not dried afterwards. The finished product is very moist and yields to the light pressure of a finger. The large fishes such as seer, black pomfrets, sharks, India salmon etc are generally treated by this method. 

Types: Brining and pickle curing are the two methods used for wet salting. Which method is used depends on whether the product will be further processed by drying or smoking, or just preserved with salting.

1. Salting in Brine

Salt concentration in brine varies from 20 to 30%. It is known that at the concentration of 25%, multiplication of micro-organisms stops. The killed fishes after being gutted, cleaned and washed are dipped in brine, containing the average of 16 to 20% or a maximum of 25% salt. After being so salted they air dried in cool shady places.

Brining requires the water used to be saturated with salt. To make the brine, mix four parts of clean water and one part of salt ( for example, 10 liters (2 gallons) of clean, fresh water to 2.7 kg-3.6 kg (6-8lbs of dry salt) in a clean, large plastic drum. Keep adding salt to the water, until no more salt will dissolve.

After the fish has been prepared according to its size, it must be cleaned and put in the brine. Place a clean piece of wood weighed down with clean stones on top of the fish to keep the fish below the surface. Stir the mixture every 20 to 30 minutes. Brining will take as little time as 30 minutes for light salting, or up to 24 hours for medium salting.  Fish for drying, smoking and canning are usually brined prior to processing.

2. Pickle curing

It requires preparing the fish according to size, cleaned before. The fish are then laid alternately with dry salt in a water-tight container, such as a plastic container, using a fish-to-salt ratio of 1 part fish to 0.3 or 0.4 parts salt by weight. That is, for 10 kg of prepared fish you must use 3 to 4 kg of clean, dry salt. If less salt is used, then the fish will spoil.

Start by weighing the fish. Calculate how much salt is needed and weigh out this quantity of salt. Place a layer of gutted, opened and washed fish pieces flat on the salt, flesh side down. In other words, flesh to flesh and skin to skin. After each layer of fish sprinkle a thin layer of salt on layer of fish. Keep placing a layer of fish then a thin layer of salt until all the fish and all the weighed salt is finished. Make sure you finish with a layer of fish, skin upwards, and a final layer of salt.

Water from the fish will quickly start to form. The surrounding salt will dissolve in this water. This is called the pickle. It is retained inside the container and will eventually cover all the fish. Place a clean piece of wood weighed down with clean stones on the top of the fish until salting is completed. This will take 36 to 40 hours for small, whole fish and three to four days for large pieces of fish. 

Wet salted fish should be consumed within 2 months of storage at an ambient temperature. It will keep for several months if stored in a cool place.

1.7.4    Drying - Sun drying

Meaning: Drying involves dehydration i.e. the removal of moisture contents of fish.

Principle: Drying is the removal of water from fish. Normally the term 'drying' implies the removal of water by evaporation but water can be removed by other methods: for example, the action of salt and the application of pressure will remove water from fish. Since water is essential for the activity of all living organisms its removal will slow down, or stop, microbiological or autolytic activity and can thus be used as a method of preservation. Like salting, drying is a very common method of preserving fish, particularly in tropical countries. When sufficient water has been removed fish will be preserved because water is essential for bacteria and enzymes to survive and work to spoil fish. When moisture contents reduce up to 10%, the fishes are not spoiled provided they are stored in dry conditions.  Drying is often used in combination with salting and or smoking for additional preservation.

Technique: Where drying has evolved as a traditional method of preserving fish, the action of the sun and wind is used to effect evaporative drying. In recent times, the controlled artificial dehydration of fish has been developed in some industrialized countries so that fish drying can be carried out regardless of weather conditions.

Sun drying is the simple method of curing fish and is extensively practiced in India. The total catch of sea fish is cured by drying in the sun. Bombay duck, Ribbon fish, silver bellies and some other small marine fishes are subjected to sun drying. Fresh water fish e.g. Labeo, Catla, and Puntius etc. These are also dried in Bengal, Assam and Bihar but in very small quantities as compared to marine fish.

Merits: It is cheapest method; do not require ice, electrical power when natural method is used.

Demerits: It is slow and results in much loss, through spoilage when natural drying is used.

Types: Fish drying is of two types.

Natural Drying

In natural drying the fishes are washed and dried in the sunshine. They are suspended on the open ground. The process has a number of disadvantages. It can be carried out only in dry well aerated climate receiving sunshine which is not too hot. Lastly only the thin fishes can be preserved by this method because the fat fishes have much flesh allowing bacterial decomposition to continue in deeper parts of their body. The process has a number of disadvantages. It is slow and results in much loss, through putrefaction.

Artificial drying

In artificial drying the killed fishes are cleaned, gutted and have their heads removed. They are cut lengthwise to remove large parts of their spinal column followed by washing and drying them mechanically.

Fig.7.2 Fish preservation- Drying

Smoking/smoke curing

Meaning: It is the method of exposing the fish to cold or hot smoke treatment. Smoking or smoke curing, like drying and salt curing is ancient methods of preservation of fish.

Principle: The phenol content of the smoke acts as an antiseptic

Technique: In this method, landed fish is cleaned and brined. It is then exposed to cold or hot smoke treatment. In cold smoking, first a temperature of 38⁰C is raised from a smokeless fire. After this heating, cold smoke at a temperature below 28⁰C is allowed to circulate past the fish. In case of hot smoking, first a strong fire produces a temperature around 130⁰C. This is followed by smoking at a temperature of 40⁰C. The smoke has to be wet and dense. Good controls are necessary over density, temperature, humidity, speed of circulation, pattern of circulation and time of contact with fish of the smoke. The phenol content of the smoke imparts a characteristic colour and flavour. Some condensation of tars and resins also adds to the taste. Strict hygienic conditions are maintained throughout this operation.

In early method of smoking, heavily salted fish used to smoke for long duration and even few weeks and the resultant products were called “hard cures”. This product has long shelf life at ambient temperature. Owing to the high salt concentration and long smoking and drying period, this lowers the water activity considerably.

Smoking is also employed as an intermediate step in processing canned smoked fish. Lightly smoked fish is considered as an alternate to fresh fish having slightly pleasant smoke flavor. In course of time the “hard cures” gave a way to milder production with less salt and lower duration of smoking. Such products however, have short shelf life.

Merits: The products stored for long time.

Demerits: Phenolic smoke to fish may not be preferred by some consumers.

Fig.7.3 Smoking

1.7.5    Canning

Meaning: Canning is a method of preservation in which spoilage can be averted by killing microorganisms through heat.

Principle: The method is based on prevention of microbial activity by heat technique.

Technique: The canning is done in following steps:

1. Fresh fishes are cleaned to removed dirt and organism present on their body.
2. Fishes are gutted and cut into pieces of suitable sizes. Their head, tail, fines and viscera are removed. The pieces are cleaned and dipped in brine to remove blood form the tissues to give proper degree of firmness and flavour to flesh.
3. Pieces are now immersed in hot water or exposed to steam to remove adhering materials, which could not be removed by cleaning with cold water.
4. The cleaned pieces are filled in cans or jars which are still hot. The open containing pieces are now passed though an exhaust box receiving steam under pressure. Exhausting expands the food, drives out the air or gas bubbles from the containers flesh and provides an atmosphere of steam in upper vacant part of the container. Containers are then immediately sealed. Heating decompose the autolysis enzymes in the flesh. Further the steam with a temperature range of 110⁰C to 120⁰C and pressure of 7kg/6.45cm² kill all the bacteria and their spores known to spoil the fish.
5. The sealed containers are again subjected to heat treatment to kill micro-organism left in flash.
6. Heating affects the character and composition of the contained flesh. A long exposure to low temperature, provided through cold water or cooled air is considered helpful to prevent any changes in the texture or flavour.
7. The raw material should be processed properly since it contains most dangerous Closetridium botulinium which should be destroyed. This is found in protein rich food such as fish which has pH 6 - 7 and is non-acidic. There are some other heat resistant bacteria like Clostridium sporogenes which can be eliminated at a temperature of 5 - 6 times more than Clostridium botulinlum. It needs a temperature of 120⁰C for 4 minutes or at 115⁰C for 10 minutes to kill them in large numbers.
8. Finally the containers are tested before their transportation to the market.

Merits: Product long lasting, kill bacteria.

Demerits: Canning is a complicated process that requires costly machinery and technical knowledge; hence, the products are costly.

Review Questions:

Long Answer questions

1.    Describe in detail any three methods of Fish Preservation.

2.    What do you mean by Fish Preservation? Describe in brief various fish preservation techniques employed in fish Industry in India.

Write short notes on the following;

a) Chilling 

 b) Freezing  

c) Salting  

d) Drying 

e) Canning

Short answer questions:

i)        Describe in detail the causes of fish spoilage.

ii)      Explain the bacterial action of fish spoilage.

iii)    Explain the chemical action of fish spoilage.

iv)    Explain the enzymatic action of fish spoilage.

Define/Explain: Dehydration, Autolysis, Exosmosis, Oxidation, Rancidity, Rigor mortis, Canning, Chilling, Freezing, Drying, Salting.

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