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Chapter: 11th Zoology : Chapter 13 : Trends in Economic Zoology


Aquaculture has been practiced in varying forms for centuries dating to the time of the Phoenicians. India offers a huge potential for aquaculture development.



Aquaculture has been practiced in varying forms for centuries dating to the time of the Phoenicians. India offers a huge potential for aquaculture development. Fish culture received notable attention in Tamil Nadu in 1911. Aquaculture is a branch of science that deals with the farming of aquatic organisms such as fish, molluscs, crustaceans and aquatic plants.


On the basis of source, aquaculture can be classified into three categories.


They are (a) Freshwater aquaculture (b) Brackish water aquaculture (c) Marine water aquaculture. Culturing of fishes is called fish culture or pisciculture. Inland water bodies include freshwater bodies like rivers, canals, streams, lakes, flood plain wetlands, reservoirs, ponds, tanks and other derelict water bodies and ponds constructed for fresh water aquaculture. The pH of the freshwater should be around neutral and salinity below 5 ppt (parts per thousand).


Brackish water fishes spend most of its life in river mouths (estuaries) back waters, mangrove swamps and coastal lagoons. Estuarine fish are more common in Bengal and Kerala. Culturing of animals in the water having salinity range 0.5 2 30 ppt are called as brackish water culture. Fishes cultured in brackish water are Milk fish (Chanos Chanos), Sea bass (‘Koduva’), Grey mullet (‘Madavai’), Pearl spots (‘Kari’meen) etc,


Marine Fisheries deal with fishing operations along seacoasts. The Indian subcontinent approximately has a 5600 kms long coastline. About 80% of India’s marine fish are supplied by the west coast and the remaining 20% by the east coast. The premier varieties are mackerels, sardines, sharks, and catfish. Marine edible fishes of Tamilnadu coast include both cartilaginous and bony fishes. Culturing of animals in the water salinity ranges from 30 - 35% is called Mariculture. Some fishes like Chanos sp, Mugil cephalus are cultured here. Culturing of animals in the salinity ranges from 36 - 40% is called Metahaline culture. Eg, Brine shrimp (Artemia salina). Artemia is commonly known as the brine shrimp. It is a crustacean and lives in high saline waters because of its high osmoregulatory capacity.


1. Fish culture


Characteristics of cultivable fishes


The special characteristic features of cultivable fishes are:

i.                Fishes should have high growth rate in short period for culture.


ii.              They should accept supplementary diet.


iii.           They should be hardy enough to resist some common diseases and infection of parasites.


iv.           Fishes proposed for polyculture should be able to live together without interfering or attacking other fishes.


v.              They should have high conversion efficiency so that they can effectively utilize the food.


Types of cultivable fish


Cultivable fish are of 3 types(Figure 13. 9).


a)              Indigenous or native fresh water fishes (Major carps, Catla, Labeo, Clarias)


b)             Salt water fishes acclimatized for fresh water (Chanos, Mullet).


c)              Exotic fishes or imported from other counties (Common carps)


Among these, major carps have proved to be best suited for culture in India, because the carps


1.    Feed on zooplanktons and phytoplanktons, decaying weeds, debris and other aquatic plants.


2.     They can survive in turbid water with slightly higher temperature


3.     Can tolerate O2 variations in water.


4.     Can be transported from one place to other easily.


5.     They are highly nutritive and palatable.


External factors affecting fish culture


The factors that affect fish culture are temperature, light rain, water, flood, water current, turbidity of water, pH hardness, salinity and dissolved O2. Light and temperature also play an important role in fish breeding.


Management of fish farm


To culture fish, one should have an idea about different stages of fish culture such as topographic situation, quality, source, physical, chemical and biological factors of water. Breeding, hatching, nursing, rearing and stocking fishes in ponds has to be managed properly. Keeping in view the various stages of fishes, the following different types of ponds have been recommended to manage them.


Breeding pond


The first step in fish culture is the breeding of fishes, therefore, for proper breeding special types of ponds are prepared called breeding ponds. These ponds are prepared near the rivers or other natural water resources.


Types of breeding


Depending on the mode of breeding, they are divided into 

1.Natural breeding (Bundh breeding)


These are special types of ponds where natural riverine conditions or any natural water resources are managed for breeding of culturable fishes. There bundhs are constructed in large low-lying areas that can accommodate large quantity of rain water. The shallow area of such bundhs is used as spawning ground.


2. Induced breeding


The fish seed is commonly collected from breeding grounds but does not guarantee that all fish seeds belong to the same species. Hence advanced techniques have been developed to improve the quality of fish seed by artificial method of fertilization and induced breeding. Artificial fertilization involves removal of ova and sperm from female and male by artificial mechanical process and the eggs are fertilized. For artificial fertilization the belly of mature female fish is held upward. Stripping is done with the thumb of the right hand from the anterior to posterior direction for the ejection of eggs due to force. In this way eggs are collected separately. Further, the male fish is caught with its belly downwards. The milt of fish is striped and collected separately, and then the eggs are fertilized.


Induced breeding is also done by hypophysation (removal of pituitary gland). The gonadotropin hormone (FSH and LH) secreted by the pituitary gland influences the maturation of gonads and spawning in fishes. Pituitary gland is removed from a healthy mature fish. Pituitary extract is prepared by homogenising in 0.3% saline or glycerine and centrifuged for 15 minutes at 8000rpm. The supernatant is injected intramuscularly at the base of the caudal fin or intra-peritonealy at the base of pectoral fin. Male and female fishes start to spawn (release of gametes) and eggs are fertilized. The fertilized eggs are removed from the spawning place and kept into hatching hapas.


Fish seed


Fish seed is collected from breeding ponds. The spawn collecting net is commonly called Benchijal (Shooting net) and transferred to the hatching pits


Hatching pit


The fertilized eggs are kept in hatching pits. The hatching pits should be nearer to the breeding grounds, should be smaller in size with good quality water. There are two types of hatching pits, hatcheries are small sized pond in which unfertilized eggs are transferred and hatching happens. Hatching hapas are rectangular trough shaped tanks made up of mosquito net cloth supported by bamboo poles and fixed in the river (Figure 13.10).


Nursery pond


The newly hatched fries are transported from the hatching happa to nursery ponds where they grow into fingerlings.


Rearing pond

Fingerlings are transferred to rearing ponds that is long and narrow and allows long distance swimming. The rearing pond should be free from toxicants and predators. Antibiotics are used for washing the fingerlings and then transferred to the stocking ponds.


Stocking ponds


Stocking ponds should be devoid of weeds and predatory fishes. Proper organic manuring should be done to increase the production with cow dung and chemical fertilizing should also be done.




Harvesting is done to capture the fishes from the water. Well grown fishes are taken out for marketing. Small sized fishes are again released into the stocking ponds for further growth. Different methods of fishing are carried out to harvest fishes. These include Stranding, Angling, Traps, Dipnets, Cast nets, Gill nets, Drag nets and purse nets. The harvested fishes are preserved by refrigeration, Deep freezing, freeze drying, sun drying, salting, smoking and canning.


Composite fish farming


Few selected fishes belonging to different species are stocked together in proper proportion in a pond. This mixed farming is termed composite fish farming or polyculture. The advantages include,


1.              All available niches are fully utilized.


2.              Compatible species do not harm each other.


3.              No competition among different species is found.


4.              Catla catla, Labeo rohita and Cirrhinus mrigala (surface feeder) are the commonly used fish species for composite fish farming.


Exotic fishes


The fishes imported into a country for fish culture are called exotic fishes and such fish culture is known as exotic fish culture. Examples of such exotic fishes introduced in India are Cyprinus carpio and Oreochromis mossambicus.


Disease Management


Diseases can be of viral or bacterial origin. Regular monitoring of parameters like water quality, aeration, regular feeding, observation for mortality should be checked. Parasitic infestations and microbial infections should be observed periodically.


Economic importance of fish


Fishes frrm a rich source of protein food and provide a good staple food to tide over the nutritional needs of man. Fish species such as sardines, mackerel, tuna, herrings have high amino acids concentrations particularly histidine which is responsible for the meaty flavor of the flesh. It is rich in fat such as omega 3 fatty acids. Minerals such as calcium, magnesium, phosphorus, potassium, iron, manganese, iodine and copper. Some of the fish by - products are;


Fish oil is the most important fish by product. It is derived from fish liver and from the fish body. Fish liver oil is derived from the liver which is rich in vitamin A and D, whereas fish body oil has high content of iodine, not suitable for human consumption, but is used in the manufacture of laundry soaps, paints and cosmetics.


Fish meal is prepared from fish waste after extracting oil from the fish. The dried wastes are used to prepare food for pig, poultry and cattle. The wastes obtained during the preparation of fish meal are widely used as manure.


Isinglass is a high -grade collagen produced from dried air bladder or swim bladder of certain fishes viz. catfish and carps. The processed bladder which is dissolved in hot water forms a gelatin having adhesive property. It is primarily used for clarification of wine, beer and vinegar.


2. Prawn Culture


Most important aquatic crustacean is prawn, which is widely cultured prawn flesh is palatable and rich in glycogen, protein with low fat content.

Types of prawn fishery


1.              Shallow water prawn fishery – located on the west coast restricted to shallow waters.


2.              Estuaries and back waters or saline lake prawn fishery - The area of production of prawns are the back waters seen along the Western coast, Ennur, Pulicat, Chilka lake and Estuaries of Ganga and Brahmaputra rivers.


3.              Freshwater prawn fishery - Prawns are caught from the rivers and lakes throughout India.


4.              Marine prawn fishery – Most of the marine prawns are caught along the Indian coast belonging to the family Penaeidae.


Species of prawn


A number of species of prawn are distributed in water resources such as Penaeus indicus, Penaeus monodon, Metapenaeus dobsoni and Macrobrachium rosenbergii.


Culture of freshwater prawn


Macrobrachium rosenbergii (Figure 13.11) is commonly seen in rivers, fields and low-saline estuaries. The prawn collected from ponds, river, and paddy fields are transferred to the tanks which are aerated. For fertilization, one pair of prawn are kept in a separate tank. After mating, the eggs are laid. Spawning tanks of different sizesshould be prepared with proper aeration. Temperature (240 C – 300 C) and pH (7- 8) should be maintained in the hatching tank. The eggs hatch into first and second stage larva. Artificial feed is supplied. Young ones of 5cm length (60 days old) can be reared in fresh or slightly brackish water ponds and rice fields. Harvesting of prawns can be done twice in a year.


Culture of marine prawn


Several factors that determine the success of marine prawn culture includes selection of site, water quality, soil quality and availability of seed.


Preparation of farm


For the preparation of ponds for algal growth and for the subsequent stocking of prawns it is essential to drain off the water and sundry the bottom followed by light tilling.


Agricultural lime should be applied to absorb excess CO2 and to supply calcium which is required for moulting. Fertilizers like rice, bran, poultry, and cattle dung are used to increase the fertility of the soil. Prawns are commonly caught in crafts and gears using different types of nets such as cast nets, bag nets, drag nets, trawl nets and barrier nets. Preservation of prawns is done by peeling and deveining or by cooking and peeling.


3. Pearl Culture


Pearl is a white, highly shining globular concretion found within the shell of an Oyster. Pearl oysters are sedentary animals. In India it was cultured for the first time in 1973 at Thoothukudi. Pearl oysters are found along the coast of Kanyakumari and in the Gulf of Kutch. High quality pearls are obtained from pearl oysters of Genus Pinctada that can be cultured in the salinity range of 30 ppt in racks, raft and long line methods. Freshwater bivalve Lamellidens is also used in artificial pearl culture. Mostly the pearl oysters inhabit the ridges of rocks or dead corals, forming extensive pearl banks. These pearl beds produce best quality of pearls called as “Lingha Pearl”.


Pearl Formation


When a foreign particle accidently enters into the space between mantle and shell of the oyster, it adheres to the mantle. The mantle epithelium encloses it like a sac and starts to secrete concentric layers of nacre around it as a defensive mechanism. Nacre is secreted continuously by the epithelial layer of the mantle and is deposited around the foreign particle and over a period time the formation of repeated layers of calcium carbonate makes the hard and glossy pearl. When the pearl enlarges the oyster dies. The shell is then carefully opened and the pearls are manually separated and graded (Figure 13. 12).


Programming of Pearl Industry and Artificial Insertion of Nucleus


This can be achieved by an artificial device to insert the nucleus as foreign particle in the shell of oyster has proved useful for the production of pearls in greater number.


i. Collection of oysters


Oysters are caught by special type of cages (84 x 54 x 20 cm) by covering a heavy wire frame with two centimeter wire mesh. This cage is dipped into a sand-cement mixture providing rough surface to the cages to which free swimming spat get easily stuck up. These cages are suspended at a depth of 6 meters. From July to November, where spats are easily available. These collected oysters are now transferred to rearing cages.


ii. Rearing of oysters


The collected oysters are stocked and reared in special type of cage called as rearing cage. These cages are well protected from enemies of oysters like Octopus, Eel, Devil fishes etc. The collected oysters are first cleaned and then placed into the culture cages for a period of about 10 to 20 days to recover from the strain due to excessive handling and for the physiological adjustment to the shallow water conditions.


iii. Insertion of nucleus


In this method, a piece of mantle of living oyster is cut off and inserted together with a suitable nucleus inside the living tissue of another oyster. Following steps are taken for the insertion of nucleus.


a. Fitness of oyster for operation


The selected oysters for the insertion of nucleus should be healthy and strong enough to overcome the stress during operation


b. Preparation of graft tissues


The piece of tissue which is inserted inside the mantle is called as ‘GRAFT’ tissue. The outer edges of these graft squares must be known because nacre secreting cells are found only on the outer surface of the mantle so it is essential to keep the outer surface in contact with the inserted nucleus.


c. Preparation of nucleus


Any small particle may function as nucleus to initiate the pearl formation but it is reported that calcareous nucleus is the best because the deposition of nacre was found to be more on calcarious nucleus.


d. 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 main mass one graft tissue which functions as a bed for the nucleus.


e. Post operation care


Nucleated oysters are placed into cages and suspended into sea water and attached with floating rafts to a depth of 2 to 3 metres for about 6 to 7 days to recover from the shocks due to operation. This period of 6 to 7 days is known as ‘Recovery period’. About 3000 to 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


Pearls are harvested in the month of December to February which may slightly vary according to climatic conditions. After the completion of 3 years of the insertion of nucleus, pearl oysters are harvested from the sea and the pearls are taken out from the shell.


v. Clearing of pearls


After taking out the pearls from the oysters shell they are washed properly, cleared with the soap solution.


Composition of pearl

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

(1) Water: 2-4%

(2) Organic matter:3.5-5.9%

(3) Calcium carbonate: 90%                                                                       

(4) Residue: 0.1-0.8% carbonate: 90%


Quality of pearl


The pearls obtained are of variable shapes and sizes. They may be white, or cream red or pink red in colour. The spherical pearls of rainbow colour are rarely found. The best quality of pearl is obtained from marine oysters. Pearl obtained from freshwater bivalves are not as valuable as those obtained from the marine oysters (Mishra, 1961).


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