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Model Answer of AU-7025 B.Sc. (R.T.) IV Semester – 2015

RTZ-404: Aquaculture Section- A

Q.1 Objective Type Questions: (i) All (ii) Marine water bony fishes (iii) Ganga (iv) Gambusia (v) Both (a) & (b) (vi) Kept in ice (vii) Lingha (viii) All (ix) Pinctada vulgaris (x) CaCO3

Section- B Short Answer Type Questions: Q.2 Write a detail account on colouration in fishes:

-Colouration is due to presence of various kinds of pigments in integument. -Coloured fresh water fishes are- Carassius (Gold fish), Colisa, Botia, Noemechilus, etc. Botia has black bands against yellow or orange background. Colisa has 14 orange coloured bands running obliquely from the back to the ventral side with greenish-blue background and blue spots on the operculum. Mystus vittatus has golden colour with three or four longitudinal black stripes on each side. Colour is due to chromatophores and irridocytes. -Chromatophores : These are branched cells present in the dermis and contain pigments like carotenoids (Yellow, red), melanin (black), purines/guanine (white or silvery), flavins, porphyrins, etc. and cells are erythrophores (Red/Orange), xanthophores (yellow) and melanophores (black). -Other colours like blue, green or brown are due to mixing of these three chromatophores in various proportions. -The yellow, red and orange pigments are taken through food while the black pigment is the result of breakdown of amino acid (Tyrosine—melanin). -Irridocytes (Mirror cells): These have great reflecting power and contain guanine which is white, opaque or silvery crystalline. Both type of cells are present above and below the scales. Chromatophores are more in dorsal surface while irridocytes in ventral. The relative number of chromatophores, kinds of pigments present in them, and the manner of their distribution on the body results in a variety of colour patterns seen in the fish species. Sword tail fish (Xiphophorus helleri) contains xantherythrophores which show yellow-red-orange patterns of colour. -Change in colour (Metachrosis): Fish can change their colour to adjust in their surroundings. A temporary change in colour is affected rapidly by rearrangement of pigment granules but a semi permanent change occurs slowly by an increase or decrease in the total number of chromatophors. -In light: Aggregation of pigments- light skin colour. -In dark: Distribution of pigments-dark skin colour. -Colour change takes different times in variousspecies. -Other factors are age, sex, health and emotions. -Mechanism of colour change: It is co-ordinated by nerves or hormones or both. -Other reasons may be contraction and relaxation of fibrils present between outer and inner membranes and change in electric potential to cause movement of pigment granules (Oryzias). (1) Neural control: Neurons-Neurohumors-activation. -First type neurohumors -Pigment dispersion. -Second type neurohumors- Pigment aggregation. -Cutting of nerves supplying to a particular area influences the chromatophores of that area (Phoximus) -Neural control brings about a rapid change in the colour but control through hormones is relatively a slow process. (2) Hormonal control: Under the control of pituitary -Hypophysectomy- light colour due to aggregation, if pituitary extract is injected colour is restored temporarily -MSH brings dispersion of the pigments (Dark). -Hypothalamus releases MSH-RH and MSH-IH -Adrenalin also produces concentrating effect -Gonadal hormones and thyroxin also influence the colour of skin.

2 -Anguilla- Both hormonal (Effective and dominant) and neural control. -Fundulus- Neural control is dominant. -Sharks and Rays- Effectively controlled by Pineal body but neural control is little. -Significance and uses of colouration: -Protection by concealment from the enemy (Camouflage) -To catch the prey by by disguise (Concealment and disguise) -For sex recognition during mating -To deceive the enemy or to attract the prey -Useful in classification -Probably colouration is under genetic control and is a means to identify a species. Q.3 Write a short note on air breathing organs in fishes:

-Some tropical fishes have special accessory air breathing organs, hence are unique in their ability for bimodal mode of respiration. -These structures have generally developed in response to the unfavourable environmental conditions such as living in foul water or out of water for short periods and enable the fish to tolerate O2 depletion in water. -Generally, some existing organs have become highly vascular and modified for aerial respiration. -The organs so modified are skin, gills, branchial cavity, air bladder or the intestine. -These are rarely seen in marine fishes. -In a few species, new structures have developed for this purpose, and these are called neo-morphic organs. -Skin: The skin becomes highly vascular and is kept moist by mucous so that exchange of gases takes place between blood and air eg. Anguilla, Amphipnous, Mastacembulus. -These fishes move out of water and migrate on land for short distance, in search of another suitable water body, comparable to that of frog eg. Rita. -Gills: eg. Rita, Mastacembelus- the unmodified gills secrete large amount of mucous to keep them moist and exchange of gases continues for some time, when the fish is out of water, can be seen in fish market. -Alimentary canal: Stomach or intestine becomes modified for aerial respiration. eg. Loaches (Misgurnus fossilis). -Wall becomes extremely thin -Blood capillaries increased in number -Muscles are greatly reduced. -Air is swallowed and forced into the alimentary canal where it is stored for some time. After the gaseous exchange, the air is passed out through the anus or mouth. -Air bladder: eg. Polypterus, Amia, Lepidosteus and Dipnoi, the swim bladder is highly vascular, compartmentalized into alveoli and sacculi to function as a lung. -In lower actinopterygeans, the air bladder serves for respiration as well as a hydrostatic organ. -In Dipnoi, lungs are comparable with the lungs of amphibians. -In Notopterus, swim bladder has a wide pneumatic duct and a network of blood capillaries covered by a thin epithelium in its wall. -Bucco-pharynx: Highly vascularised epithelium eg. Periphthalmus, Amphipnous, Electrophorus. -In Channa- superficial cavities are formed in the roof of the pharynx which are highly vascularised and have alveoli also and open antero-ventrally into the bucco-pharynx and postero-ventrally into the opercular cavity. -Opercular cavity: eg. Periophthalmus, Boleophthalmus.

3 -Opercular cavity form two little balloon like structures in the hinder region of the head, and inhaled air is passed through the gill slits and is stored for some time in the cavity and the balloons, both are highly vascularised. After gaseous exchange, the air is passed out through the external branchial aperture. -Following modifications are seen in the opercular cavity: (a) Large and extands below the basibranchials and above the gill arches. (b) Epithelium is highly vascularised. (c) Opercular bones are thin and elastic (d) Efficient mechanism has been evolved for closing and opening of the inhalant and exhalant apertures. -Air Breathing Organs in some Teleosts: (1) Heteropneustes: Consists of two air sacs, fans and respiratory membrane: -One pair, originate from suprabranchial chamber of the opercular cavity, thin walled, highly vascularised and lie embedded between the myotomes of the body, extending upto themiddle of the caudal region. -Receives blood from afferent air sac vessel which open into an efferent air sac vessel. -Gills of this fish bear four fans, one on each gill arch(04) -Respiratory membrane lining the air sacs is highly vascularised. (2) Anabas: Consists of a specious air chamber and a labyrinthineorgan on each side, which opens into the bucco-pharyngeal and opercular cavity. Both are covered with respiratory membrane. (3) Clarias: Consists of a pair supra-branchial chamber, two air trees or rosettes, fans and respiratory membrane. -Suprabranchial chamber is situated above the gills, lined by respiratory membrane, divided into two cup like compartments, also lined by respiratory membrane. Gill filaments are fused to form four fans, one on each arch. Gill filaments also serveas respiratory organ. -The supra-branchial chamber has inhalant and exhalant apertures. -The fish frequently rises to the surface of water and gulps in air, which enters thesupra-branchial chamber through the inhalant aperture which is a narrow slit between the second and third arch. The air entering the opercular cavity is directed into the supra-branchial chamber by the action of the fans. The slit between the third and the fourth arches is used as the exhalant aperture, and the air, after gaseous exchange is passed into the opercular cavity and then to the exterior. -Diurnal fluctuations in aerial respiration: These fishes are nocturnal in habit (inactive in day) because DO is low in mid night, and rest during the day. -During night, these fishes become active and need more O2, hence fishes frequently rise to the surface to gulp in air. -O2 and CO2 act as the ‘Steering Wheel’. -Significance: Accessory respiratory organs help the fish to survive in oxygen deficient water. -Absorption of O2 is greater in the air breathing organs, than the excretion of CO2. -Evolved during tertiary period of the Cenozoic era (70 million year ago) due to deficiency of O2 in water and air. Q.4 Describe the type and importance of plankton: -Plankton were first recognized by John Miller (1845) and the term plankton was coined by Vistor Hensen (1887). Plankton means “Wanderer”. These are pelagic and floating. -Microscopic organisms which are suspended in water and moved by water current are called plankton. Single organism is called plankter. These occur in all kind of natural waters. -Types of plankton: (1) Microplankton: These are less than 3 mm in size. (2) Nanoplankton: These are 50-60 µ in size. (3) Macroplankton: These can be seen by naked eyes (4) Bloom: It is dense community of plankton (5) Phytoplankton: These are autotrophs and form first trophic level of pond (6) Zooplankton: These are heterotrophs and form second trophic level of pond (7) True plankton: These develop and grow locally in the water of an ecosystem (8) Drift plankton: These are brought into an ecosystem from some other ecosystems (9) Haloplankton: These complete their life cycle in drifting state (10) Meroplankton: They remain free floating up to certain stages in their life cycle (eggs and larvae) (11) Hypoplankton: These live on or near the bottom (12) Ultraplankton: These are most smaller forms of plankton (13) Tychoplankton: The organisms which have become accidently plankton. -Basically, there are two forms of plankton which play important role in fisheries. (1) Phytoplankton: These fall into following classes: (a) Chlorophyceae: Spirogyra, Zygnema, Cosmarium, Pediastrum, etc. (b) Euglenophyceae: Euglena and Phacus.

4 (c) Bacillariophyceae: Fragilaria, Gomphonema, Navicula, Diploneis, etc. (d) Cyanophyceae: Microcystis, Anabaena, Nostoc, Oscillatoria, etc. (e) Dinophyceae: Ceratium, Ferdinium, etc. (2) Zooplankton: These are included in the following groups: (a) Protozoa: Diflugia, Paramecium, Arcella, Euglypha, etc. (b) Rotifera: Brachionus, Filinia, Rotaria, Keratella, Polyarthra, Asplanchna, etc. (c) Cladocera: Daphnia, Moina, Sida, etc. (d) Coprpoda: Nauplius, Diaptomus, Cyclops, etc. (e) Ostracoda: Cypris, Stenocypris, etc. (f) Sponges: Heteromyeria, Meyenia, etc. (g) Insects: Larvae of aquatic insects and mosquitoes. -Bloom: When plankton attain enormous density 20 to 100x103 cells/ml of water is called “water bloom or tides “. In fish pond, it generally occurs due to either intensive fertilization or feed wastage. It is developed within 3-4 days. -Generally blooms are either algal or zooplankton type but both types are dangerous to the fish forms. Algal bloom consumes all DO in nocturnal respiration or by increasing BOD. If algal bloom dies, it leads to suffocation of the fish stock. Some algae produce toxins (Dinoflagellates, chrusophytes and cyanophytes) which kill the fish. The bloom coat the gills so fishes are suffocated. Dinoflagellates (Marine red tides) releases toxins after death which is tetrahydopurine derivative. Chrysophytes (Phytoflagellates) are brackish water species produce extracellular toxins. Cyanophytesalso produce toxins like Microcystein. Besides these, algae also impart a disagreeable odour to the fishes. -Control of toxinogenic blooms: Prymnesium (Israel), Microcystis and certain zooplankton form blooms. These can be controlled by following methods: (1) Use of aqueous ammonia: 2-3 ml/litre for Prymnesium bloom. (2) Use of lime, manure or phosphates: Adjust the pH of water which is detrimental to the Microcystis bloom. (3) Use of chrotoxyphos: 0.1-1.0 mg/l, to control zooplankton bloom. -Plankton productivity: The quantitative measures of the plankton production can be expressed by the standing crop, annual crop and average individual weight of each kind of plankton in different environmental conditions, show maximum biomass in the month of July (monsoon growth) and decline in last winter and summer months. Plankton peaks are recorded in monsoon and spring months. -July and August- Volvox period; Sept. to Nov.- Copepode period; Dec. and Jan.- Cladoceran period; Feb. and March- Cyanophycean period and April to June- Ostracode period are the some important peaks of plankton. -Significance of plankton: (1) In fisheries: phytoplankton are autotrophs on which zooplankton feed. These zooplankton are fed by fish and other organisms. In a fish pond, plankton form the most abundant base of the food web to increase the fish production. Rearing and growth of a particular fish species can be carried out in a pond with abundance of plankton. Inorganic nutrients are essential for the growth of plankton. Phytoplankton Insects Fish Death and Decay Zooplankton Detritus (Food web in a pond water)

(2) As human food: About 45-60 million tons of plankton are used as human food round the world. (3) Hygienic value: Phytoplankton utilize inorganic plant nutrients and replace CO2 by O2.

(4) Other applications: Bottom deposits of extinct diatoms are powdered and used in cleaning utensils and in metal polishing. Diatoms are used as absorbent of nitroglycerine in dynamite industry. These also used as filter in sugar and rubber industries, used as cement, to insulate furnaces, used in manufacturing of chalk and lime stone. Q.5 Describe the economic values of fishes: -From ancient time, fish are utilized as rich source of food. The importance of fish as food resulted in the development of fisheries as an industry. India is among first ten highest fish producing countries in world. -Following are the important economic values of fish for human and others: (1) Fish as food: (a) Fish as human food: Fish contains large amount of proteins, fats, carbohydrates, minerals, vitamins, etc. these also provide all essential amino acids, hence have great food value.

5 (b) Fish as cattle food: The fishes having little food value along with scrap from canneries are dried and ground. It is now cooked and pressed to remove oil and water (cakes). Cakes are dried in sun light which is called as fish meal for cattle, pig and poultry which increases milk and egg production. (2) Fish oil: It is the byproduct of fish industry. (a) Fish liver oil: It is prepared from liver of sharks and rays which have medicinal value (Vit. A & D). (b) Fish body oil: It is extracted from the body of low quality fishes. It is poor in vitamins. The left mass is used to prepare fish meal. Fish oil forms useful material for cottage and large scale industries. It is used in manufacturing of paints, warnishes, cheap soap, candles, certain chemicals, cosmetics, lubricants, painting ink, etc. (3) Fish manure and Guano: Low quality fishes are dried and ground to form manure. Fish guano is the byproduct of oil extracting industries. It decomposes quickly and can be used as manure. (4) Fish silage: Fishes are minced and mixed with dilute H2SO4 and formic acid, and this product is used as animal food having high nutritive value. (5) Fish glue: The raw materials of fishes are minced, steam heated and covered with acidic water. The liquid is extracted and concentrated to form glue. It is used as adhesive, for making paper boxes, shoes, furniture, etc. (6) Isinglass: Air bladder of the fish is dried in sun and powdered. It is used for clearing wine, bear, making edible jelly and in preparing the adhesive. It is also used in confectionary as a substitute for gelatin. Russian isinglass of sturgeons is of high quality. (7) Fish leather: Skin of cods, sharks and rays is used as leather. Skin is treated, dried and then tanned. It is prepared to manufacture shoes, bags, suitcases, ornamental articles, etc. (8) Sahgreen: It is dried skin of sharks. It is used for smoothening wooden articles and polishing. (9) Fish sausage and soup: It is used in Japan, Russia and USA. Meat is mixed with salt, sugarand spices to improve taste and flavor (fish sausage). Fish soup is prepared from fins of sharks which are exported to China. (10) Fish flour and biscuits: High quality fish flour is mixed with wheat flour and baked to prepare biscuits. (11) Artificial pearls: Silvery colour of fish scales contain guanine which is used to prepare artificial pearls. (12) Insulin: It is extracted from pancreas of sharks and large sized fishes. (13) Biological control: Larvivorous fish like Gambusia, Puntius, Esomus, Rasbora, etc. are used to control mosquitoes population. (14) Aquarium/Ornamental fishes: Angel fish, Carassius, Kissing gourami, Betta, black molley, etc. -Some fishes are highly poisonous (eg. Scorpion fish, Sting ray, etc.) and some are intermediate hosts to parasites, causing diseases to men and other animals. Q.6 Describe the culture of fresh water prawns: -Total species are 100, 25 are Indian species, 10 species of freshwater prawns are commercially important. -Most valuable and culturable freshwater prawn is Macrobrachium rosenbergii, suitable in polyculture. -Distribution : Indo-west pacific region, from N-W India to Vietnam, Philippines, New Guinea and N. Australia. It can tolerate maximum salinity up to 20 ppm. It migrates to estuarine water for breeding and after attaining juvenile stage, it returns to freshwater. -Identifying features : (1) In Penaeid group, abdominal pleurae are regularly arranged just like tiles of a roof while in Palaemnoid group, the pleura of second abdominal segment grows anteriorly over the first and posteriorly over the third segment (2) Second pair of leg is chelate (3) Male gonopore is situated on coxa of fifth leg while female gonopore on the coxa of third leg. -Feeding habit : These are omnivorous, chelate legs with third maxillipedes help in feeding. Larvae feed on zooplankton. -Seeds: Two methods : (1) Collection of seeds from natural sources during high tide by scoop net (2) Production of seeds in hatcheries (A) Hatchery phase : Berried prawns are induced for breeding and larvae are reared up to post larval stage for collection. Hatchery should be equipped with all modern facilities. For 10 pairs of prawns, 200x100x40 cm sized tank is required. After hatching, larvae are kept in rearing tanks with 4-5 ppt salinity of water. From second day onwards larvae are fed with desired food. -Egg Custard: Eggs-2, Milk powder- 40gm, Corn flour- 40 gm, Cooked shrimps and prawns- 40gm, Yeast- 2gm, Agar- 4gm, cod liver oil- 1ml, Vitamins + Minerals- 1gm. Other foods are powdered dried chicken blood, phytoplankton, fish meal, etc. -Feed at the rate of 30% of total body weight of larvae/day.

6 -Uneaten food and excreta should be siphoned off twice daily otherwise will cause fungal infection. -Prawn larvae are sensitive to nicotine, hence avoid smoking near tank. -Larvae metamorphose into post-larvae in 35-40 days, appear as juvenile prawns which are benthic in nature. Stones, shells, etc. are placed on bottom to provide shelter for the freshly moulted juveniles thus deterring cannibalism. Then larvae are transferred into grow-out-ponds. (B) Nursery Phase : This is a connecting link between hatchery and culture phase. -Post-larvae are allowed to develop into juvenile stage up to 2-3 cm. -Tanks of 50-200 sq.m are used as nursery. -Post larvae are fully acclimatized to fresh water. -Post-larvae are stocked at the rate of 2000 t0 3000 per sq.m. -Post-larvae have a habbit of sticking to some objects hence polythene ribbons and other similar objects are provided in nursery pond. -Feeding regime could be in the form of Moina, Chironomus larvae, pieces of earthworm or mussel flesh, acetes or pellets prepared from rice bran and ground nur cake. Moina is given at the rate of 10-15 per larva while rest of the food is given at the rate of 10% of their body weight. Fed 3-4 times daily. Culture Technology: (1) Site selection :Soil with water holding capacity (Sandy-loam, sandy-clay loam, silty-clay, silty-clay loam). (2) Pond: Ideal size of pond varies from 0.2-1.0 hectare. Rectangular pond of L:W ratio-2.5:1.0 is suitable with sloping at deeper end for an easy harvesting. Depth varies from 0.75 to 1.5 m. -With inlet at shallow end and outlet at deeper end. -Soil erosion should be prevented. (3) Water quality: Temp. 18-340C, pH 7.0-8.5, DO 5-8 ppm, hardness 40-150 ppm, PO4 and NO3 less than 1.0 ppm. -Maintain optimum water quality. A portion of water should be exchanged daily to maintain water quality and to stimulate moulting for acceleration of growth and production. Inlets and outlets should be guarded with screens. (4) Aeration: By exchange of water, producing rippels in the flow channels and injecting water over the pond. (5) Pond Management: Prawn free pond is drained and allowed to dry, mud is taken out, limed and tilled, helps in maintenance of pH and pond sanitation (Lime-200 to 500 Kg/hectare, pH-8.0), pond is filled up to 50 cm, manuring-dried chicken manure, 100-200 Kg/ha or composted cattle dung-150-200 Kg/ha, and urea 25-40 Kg/ha, then pond is left to allow the growth of natural food. When pond turns light green, more water is filled up to 1.2 1.5 m. (6)Stocking: After 15 days of manuring, 3-4 weeks old post-larvae are stocked and acclimatized before, otherwise causes heavy mortality (For pH, salt and temp.). Male grows faster than female. Monosexculture is done. (7) Food and Feeding: Prawns feed at night. Both natural and artificial food are supplied for quick growth. -Food: Pieces of rice, oil cake, Topica roots, snails, mussels, prawns and fishes, compound pellets with 25-30% proteins. -Feeding: Quantity of food is adjusted. Food is spread around the shallow margin, two times daily (Early morning and late evening). Feeding rate starts with 10-20% of the prawns body weight and is gradually reduced to 2-3% towards harvest. In order to avoid cannibalism, prawns should be prevented from hunger. (8) Growth and Survival: Survival rate is 60-70%, periodic harvesting, rearing period 6-8 months, production 1000±500 Kg/ha/year. (9) Harvesting: Large sized prawns are caught with drag net of 4-5 cm mesh. Prawns are also collected by cast net. Drain harvesting may also be carried out. Water is drained through screened pipe and remaining prawns are caught by hand picking from the mud (Time required- 20 hrs/ha). Harvesting is done in morning when it is cooler.

7 Q.7 Describe the artificial method of pearl formation:

Structure of Shell and mantle: Body is covered by two calcareous shells. Two lobes of mantle encloses mantle cavity and secrete shells. -T.S. of Shell: Shell is composed of three layers: (1) Periostracum: Outer layer, composed of concholin. (2) Prismatic layer: Middle layer, composed of calcite and thin layers of concholin. (3) Nacreous layer: Inner layer, composed of nacre (Mother of Pearl), consists of aragonite and concholin. Nacreous layer is secreted by mantle. -T.S. of Mantle: It is composed of three layers (1) outer layer containing nacre secreting cells (2) Middle layer containing connective tissue and (3) Inner layer containing ciliated epithelium. -Mechanism of Pearl formation: It is a abnormal and defensive response of pearl oyster. When a foreign particle is entangled between shell and mantle, it causes irritation. It causes stimulation of mantle and nacre secreting cells secrete nacre around material, resulting in a pearl formation. Pearl is taken out and then processed. -Artificial method of pearl formation: Oysters are collected by divers, tied with rope and basket. -Collected oysters are kept in rearing cages covered with nylon or wire mesh. Cleaned oysters are kept in culture tanks for 10-20 days, so they can acclimatize themselves in the changed environment. (1) Preparation of graft tissue: Piece of the tissue inserted into the body of oyster is called graft tissue. 2x2 mm size of mantle is cut, outer surface is with nacre secreting cells. (2) Preparation of nucleus : A calcareous nucleus is best for deposition of nacre. It is cleaned and dried before use. (3) Insertion of nucleus: Anaesthetized oysters (with methanol spray in water) relaxe adductor muscles so valve can be opened easily. Best implantation site is ventral surface of gonad. Gonads are opened through foot and graft tissue with nucleus is implanted, keeping the outer surface of graft tissue (mantle) in the contact with the inserted nucleus. -One or two or many nuclei may be transplanted. -After insertion, anaesthetized oysters should be recovered in flowing sea water (starts opening and closing of valves). (4) Rearing of oysters: Now these oysters kept in cages are hanged in sea water at a depth of 6-10 feet, in one week oysters get themselves recovered, dead ones are removed. They are kept undisturbed for a period of 03 years. Periodic monitoring should be done by sampling to decide actual time of harvesting. (5) Harvesting of Pearls: During low temperature and pH (Dec.- Feb.) pearls are recovered, same oysters may be reused.

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Section- C

Long Answer Type Questions: Q.8 Write a detail account on the scales present in the fishes:

-Scales are of two types according to their origin: (a) Placoid scales: Develop from epidermis as well as dermis and characteristically found in the elasmobranchs. (b) Non-placoid scales: Develop from dermis only, found in teleostean fishes (Cosmoid, ganoid, cycloid, ctenoid, etc.). -Placoid scales: Consists of a basal plate and a spine, giving a rough surface to skin. Basal plate if formed of a substance resembling the cement of teeth, secreted by the dermis. The spine develops from the malpighian layer of the epidermis -The outermost covering of spine is made of vitrodentine while inner layer is dentine which encloses pulp cavity. Tha basal plate has an aperture through which blood vessels and nerves of the dermis enter into the pulp cavity -The placoid scales do not overlap each other -Ecto-mesodermal in origin, resemble teeth in basic structure, hence both are homologous structures. -Cycloid scales : Thin, transparent, roughly rounded -Shows alternate ridges and grooves -Ridges or circuli are concentric rings –Central part is focus -Oblique grooves or radii running from the focus to the margin -Dermal in origin -First appear on the caudal peduncle of the larva and then on the remaining body -Project diagonally in an imbricating pattern, forming a protective covering over the body -The circuli or ridges are less distinctlyseen in the posterior part of thescale to whichchromatophores are also attached eg. Carps (Teleosts). -Ctenoid scales: Basically similar to the cycloid scale -Has a serrated margin and spines on posterior part eg. Perciform fishes (Anabas, Nandus, Channa). -Cosmoid scales : Found in extinct crossopterygii and dipnoi. In living crossopterygii (Latemeria) anddipnoi have modified to look like cycloid -Outer layeris vitrodentine while inner dentine likecosmine which is non-cellular and contains branching tubules and chambers. The inner most layer is made up of a vascular, bony substances called isopedine. -Ganoid scales : Heavy scales found in primitive Actinopterygian fishes(Ganoid fishes) eg. Acipenser, Lepidosteus and Amia -Outer layer is ganoine, middle layer cosmine and inner is isopedine, rhombic plate like, fitting edge to edge. -Uses of scales : Protection- Modified into teeth in sharks in catching prey -Teeth of thePristis are modified scales -Sharp cutting blades of the base of the tail of surgeon fish (Acanthurus) are also modified scales -Scales modified into spines for protection in Tetradon (Puffer fish) and Diodon (Porcupine fish) -The Ostracion (Coffer fish) is protected by a rigid protective box formed by articulating bony plates formed by scales -Bony rings of sea horse and pipe fish are modified scales. -Feeding: In several species, scales become modified to form gill rackers to filter the water for collecting planktonic food material. -Classification : Helpful in the classification of fishes. -Age determination : Used in calculating the age of fishes. -Food habits: Useful in identifying food habits of piscivorous animals.

9 Q.9 Describe digestive system of fish:

-Digestive system mainly incorporates food, feeding, digestion and absorption and also the elimination of undigested wastes. -The digestive system of fish includes the digestive track and various associated glands: -Alimentary Canal: Comprises of the following parts: (1) Teeth: These are hollow cones of dentine and continuously born along the inner margins of the jaws. Teeth are generally polyphyodont which are replaced by the newer ones from behind. -The number, distribution, degree of permanence, shape and mode of attachment of teeth varies among the fishes. -In cyprinids, teeth are absent. (2)Tongue: Arises from the floor of the buccal cavity and is devoid of any muscles but supported by hyoid arch. Small papillae, sensory receptors and teeth are variably present. (3) Buccal Cavity and Pharynx: Both are not clearly marked off from each other. Gill slits are present in the pharyngeal wall supported by gill rackers which assist in ingestion and prevent ts escape from the buccal cavity through gill slits. (4) Taste buds and mucous secreting cells: Taste buds are situated on the lips and bucco-pharynx of a number of fish species or may be absent. -It appears that the presence or absence of taste buds depends upon the mode of feeding of fishes. -Mucous cells present in bucco-pharynx which secrete mucous to lubricate the ingested food for easy and smooth swallowing. -Both also present on the lips, oral valves, barbles of a number of fishes which assist in sorting out the food. (5) Oesophagus: Pharynx leads into oesophagus which in turn opens into stomach. -Actually pharynx, oesophagus and stomach are not clearly marked. -Oesophagus commonly bears ongitudinal folds to permit a greater distensibility. A large number of mucous secreting cells are scattered in the mucous. Taste buds may also be present in the mucosa. -Morphologiclly, oesophagus is a short and narrow tube. (6) Stomach: It is usually differentiated into broad anterior part, cardiac stomach and into a posterior narrower part called the pyloric stomach. -Opens into mid gut, opening is guarded by a valve. -It is meant for storage and mastication of the food. -Stomach is not demarcated externally from the oesophagus. (7) Intestine: Follows the stomach, divided into small and large intestine. Duodenum of the small intestine receives ducts from liver and pancreas. Rest part is ileum. -It is long in herbivorous but short in carnivorous. (8) Pyloric caeca: Anterior part of the intestine(Pylorous) gives rise to a number of finger like outgrowths and are called pyloric caeca or intestinal caeca.

10 -These may be blind, tubular or sac like diverticulae of uncertain functions. -These may serve as accessory food reservoirs and probably serves to enhance its absorptive area. (9) Rectum: Not demarcated from large intestine but can be distinguished by the presence of ileo-rectal valve, possess a large number of mucous secreting cells produce copius mucous to lubricate waste food and aid in easy defaecation. -Digestive glands: -Liver: Bi or tri lobed structure. A gall bladder of large size is uniformly present. -Pancreas: Highly diffused gland, attached with gut, in some it is present as hepatopancreas. -Glands in digestive tract: Mucosal lining and sub-mucosa contain digestive glands. These glands may be present in buccal cavity and pharynx. -In stomach, present in cardiac and pyloric regions. -Intestinal mucosa comprises goblet cells and the granular cells. -Rectum is almost completely devoid of digestive glands. Q.10 Describe pond management: -Scientific management of pond to get maximum fish production is called pond management. This can be achieved by (a) Pre-stocking (b) Stocking and (c) Post-stocking management practices. -Pre-stocking management of pond: (1) Drying of the pond: Pond is dried. If necessary, then it can make deep by removing soil. Fertility of pond is increased. Fish parasites, their larvae and disease producing organisms are killed. (2) Control and eradication of aquatic weeds: Macrophytes, if abundant, may reduce fish production. -These are floating type- Pistia, Wolfia, Azolla, hyacinth, etc.; emergent type- Lotus, Nymphaea, water lily, etc.; sub-merged type- Hydrilla, Vallisnaria, Ceratophyllum, etc.; marginal weeds- rooted and grow along the shallow shore eg. Typha. Ipomea, Sagittaria, etc. -Aquatic weeds in limited quantity are as food, oxygen producers, to increase fertility of pond after decay, to reduce turbidity of water, to provide shelter to fish and to form spawning bed for the fishes, etc. But excessive growth is harmful to the fishes as they obstruct free movement, oxygen depletion, accumulation of carbon dioxide at night, obstruct netting of the fish, etc. -Aquatic weeds may be controlled by three methods: (a) Mechanical method: Hand picking, uprooting, cutting, etc. (b) Chemical method: weedicides are used. These should be cheaper, easily available, non-toxic, should not pollute the water and should have no adverse effects on the fertility of pond. Eg. 2,4-D (Dichlorophenoxy acetic acid), copper sulphate, simazine, calcium cyanide, etc. (c) Biological method: By introducing grass carps and ducks. Cyprinus also controlthe weeds. Algal blooms are also helpful to control the weeds but they have a number of adverse effects on the fish. (3) Preparation of rearing ponds: A number of rearing ponds are prepared like nursery ponds for hatchling, fry and fingerlings, rearing ponds for juveniles and youngs and stocking ponds to grow the fish up to marketable size. Ponds should be prepared carefully to reduce fish mortality. Following precautions must be taken: (a) Predatory and weed fishes should not present (b) Predatory aquatic insects should not present (c) Suitable food should be available for the fish (d) different sized and age groups fishes should not rear in the same pond, otherwise they show cannibalism (e) There should not be much variation in pH, O2, and temperature. (4) Eradication of predatory and weed fishes: weed fishes multiply rapidly and consume large amount of food, so small sized major carps do not get sufficient food for better growth. -Predatory fishes: Wallago, Channa, Mystus, Clarias, Mastacembelus, etc. -Weed fishes: Puntius, Esomus, Rasbora, Oxygaster, etc. -Following methods are used to remove harmful fishes: (a) Repeated drag netting (b) Draining and drying the pond to kill burrowing fishes (c) Use of suitable fish poison eg. Derris powder containing rotenone, killed fishes are fit for human consumption after 24 hours. Other fish poisons are akhrot, kuchla, mahua oil cake, aldrin, endrin, etc. (5) control of aquatic insects: Aquatic insects feed on spawn and fry eg. Belostoma, Nepa, beetle, nymphs of dragon fly, etc. These arecontrolled by frequent netting, mixture of soap and oil. Introduction of insecticides is not advisable. (6) Fertilization of pond: It is done by using organic and inorganic fertilizers. -Liming of pond: First apply quick lime (CaO) and then lime powder (CaCO3). It raises the pH of water and is antiparasitic. It should be applied200 kg/ha before 15 days of stocking the pond with fish fry and fingerlings .

11 -Manuring: Manure may be used to increase the plankton populations.

Stocking and Post-stocking management of pond -Desirable species of fishes should be selected. Fry should be introduced when zooplankton populationis maximum. 10-20 lakhs fry per hectare should be stocked, so 2-3 crops can be raised in one season. Composite fish culture should be carried out because it gives many times more production. Fish species stocked should be fast growing. - Post stocking management includes: (a) Feeding: Natural and artificial food both should provide for fast growth. Natural food includes plankton, crustaceans, insects and their larvae, worms, mollusks, etc. Generally artificial food is of vegetable originand consists of rice, barley, wheat, pulses, leaves, tuber roots, oil cakes, kitchen wastes, etc. For Indian carps, rice bran and oil cakes are most suitable but they also feed on dried and powdered mixture of insects, shrimps, pulses, etc. Supplementary food is given daily on the basis of density of fishes. feeding should be carried out in the morning and evening and should not be changed suddenly. (b) Thinning and harvesting: Advanced fry of about 3-4 cmin size are netted and released in rearing ponds from time to time. They are given artificial food at regular intervals for maintaining fast growth, resulting in 70-80% survival of carp fry. After two months, 8-13cm sized fishes are transferred in stocking ponds. (c) Manuring: It should be carried out time to time. (d) Breeding: Natural and artificial breeding. (e) Maintenance: It includes water level, physic-chemical factors, density of fishes, artificial food, etc. Q.11 Describe in detail the pearl culture and its economic importance: -Pearl is a shining, variously tinted nacreous concretion which is secreted around a foreign body. -It is oldest known gem which is a symbol of moon. -History of Pearl culture: -Mentioned in ancient Indian and Chinese literatures. -Pearl fishery was dominant in Persian Gulf. -Ye Jin Yang of China (13th century) knew that how the pearl is obtained from fresh water mussel. -In 1890, Kokichi Mikimoto of Japan established an oyster farm, hence known as “Father of Pearl Industry”. -Tat Suhei Mise and Tokichi Nishikawa (1919) obtained first artificial pearl and patented this method resulted into Japanese monopoly. -In 1938, Madras Fisheries Centre in Gulf of Mannar and in the Sikka region of Gujarat, tried to obtain artificial pearl but result was zero. -First artificial pearl was obtained in 1973 on 25th July by Central Marine Fisheries Research Institute. -Hatchery was established at Tuticorin in 1980. -Technique for seed production of P. fucata was developed in 1981, producing 2.8 million spat per year. Now India is world leader in pearl oyster research and development. -Pearl producing sites: (1) Persian Gulf: Produces superior quality of pearls, using Pictada vulgaris. (2) Peninsula of Oman to Qatar: Situated pearl banks lie at depths of 8-20 fathoms. (3) Island of Bahrain: Situated pearl banks of high quality. (4) Iranian port city of Lingeh: Producing Lingha pearl. (5) Ceylone: Has the second rank in producing the pearls. (6) Gulf of Kutch and Gulf of Mannar in India: (7) Bay of Pak: -Pearl producing animals: -There are 70 species of pearl oysters and 28 species of Pinctada. Indian species of Pinctada are P. vulgaris, P. margaritefera, P. maxima, P. chemnitzi and P. atropurpuria. -Marine species : Pinctada, Abalone, Haliotis, Mytilus, etc. -Fresh water species : Lamellidens, Unio, Anodonta, etc. -Food of pearl Oysters: -Filter feeders, feed on phytoplankton, specific microalgae are used eg. Spirulina, Dunaliella, Chaetoceros, Isochrysis and Tetraselmis. -Maturity of gonads and environmental factors: Maturity starts at the size of 16mm (Temp. 29-32oC, DO 3.2-6.4 mg/l, Salinity 32-35%, pH 7.5-8.5), maximum in months, four phases- static phase, maturation phase, partially spent phase and shrunken phase. -Water current less than one knot to bring plankton and carry away biological wastes. Larvae are photo positive while adults are photo negative.

12 -Suitable areas: Paar regions in Gulf of Mannar, area between Kanyakumari to Kalikarai, Khaddas region in Kutchgulf and maya bundar, Hut Bay Carmorte, Wandoor areas of Andaman and Nicobar Islands. -Pearl Culture: -Main steps are: I. Collection of Pearl Oysters: Three methods: (A) Spat collection from natural environment: Spat- The term is used until oyster reaches about 2 cm in length from settlement. -Following type of collectors are used : (1) A 9m long rope is taken over which nylon tufts are fixed at a distance of 25 cm. (2) A 6m long rope having a puffy spindle of nylon threads. (3) Racks constructed from bamboo pieces fixed on Casuarina logs. The size of the racks remains 1.25x1.25 m. (4) Rens made up of string with coconut kernels. (B) Spat production in hatcheries : At a suitable site, a hatchery is constructed containing various tanks for various purposes like (1) Breeders tanks (2) Spawning tanks (3)Rearing tanks (4) Algal tanks for food. -Natural spawning occurs otherwise artificial spawning is carried out by increase in temperature, by Tris buffer solution or by the useof ammonia solution. -Males spawn first which then trigger female spawning. -After fertilization, zygote is formed which is transferred in spat of 3 mm size in 60 days. Ther are reared to gain the size of 40 mm, known as “Mother Oyster” for pearl culture. (C) Collection of Oysters: By divers,tied with rope, with basket. -Collected oysters are kept in rearing cages covered with nylon or wire mesh. Cleaned oysters are kept in culture tanks for 10-20 days, so they can acclimatize themselves in the changed environment. (II) Preparation of graft tissue: Piece of the tissue inserted into the body of oyster is called graft tissue. 2x2 mm size of mantle is cut, outer surface is with nacre secreting cells. (III) Preparation of nucleus : A calcareous nucleus is best for deposition of nacre. It is cleaned and dried before use. (IV) Insertion of nucleus: Anaesthetized oysters (with methanol spray in water) relaxe adductor muscles so valve can be opened easily. Best implantation site is ventral surface of gonad. Gonads are opened through foot and graft tissue with nucleus is implanted, keeping the outer surface of graft tissue(mantle) in the contact with the inserted nucleus. -One or two or many nuclei may be transplanted. -After insertion, anaesthetized oysters should be recovered in flowing sea water (starts opening and closing of valves). (V) Rearing of oysters: Now these oysters kept in cages are hanged in sea water at a depth of 6-10 feet, in one week oysters get themselves recovered, dead ones are removed. They are kept undisturbed for a period of 03 years. Periodic monitoring should be done by sampling to decide actual time of harvesting. (VI) Harvesting of Pearls: (Beaching)- During low temperature and pH(Dec.- Feb.) and pearls are recovered, same oysters may be reused. Composition of Pearls: Water 2-4%, Organic matter 3.5-6.0%, CaCO3(Aragonite) 91.53%, residual matter 1%, also contains small amount of albuminoid and concholin. Types of Pearls: The true pearl is characterized by its lusture and a delicate playoff surface colour called its orient colour varies with mollusks and its environment, range from black to white, other colours are cream, gray, yellow, blue, lavender, green and mauve. -The gem quality is determined by the orientation and composition of aragonite crystal layers in nacreous pearls are ranked as 3.5 to 4.0 compared with 1.0 for talc and 10 for diamonds, pearl can be scratched with a pin or any sharp edge. -Pearls are classified according to their size: Minute granular pearl Less than 2.6 mm Fine pearl 2.6 to 4.9 mm Small pearl 5.0 to 6.8 mm Medium pearl 6.9 to 8.2 mm Large pearl 8.2 mm and above -Pearls can also be classified on the basis of their overall qualities: (1) Lingha Pearls- Finest quality pearls secreted by marine oysters.

13 (2) Seed Pearls- Less than one quarter grain(9000 seed pearls weigh one ounce). (3) Button Pearls- Hemispherical in shape and attached with shell. (4) Baroque Pearls- Formed inside body, but shape is not good, largest pearls, max. wt.1860 grain -Queen pearl of America, weighed 93 grain (23.25 carate) was found in Notch Brook near Peterson, N.J. in 1857. -Processing and Artificial colouring of Pearls: -To enhance their quality and appearance. Small blemishes or scratchesare also removed byremoving the layer of nacre. A hole is drilledof 0.3mm diameter, packed in bags and steam cooked for for a couple of days so that surface impurities may be removed, and then air dried. Spots or colour blemishes are removed by placing the pearl in H2O2 and petroleum eather in different proportions and exposed to sunlight, then cleaned. -Pearls can be stained also, first bleached, if to stain pink immerse in eosin for 1-24 hours. Colour can also be manipulated by using differently coloured nuclear beads during implantation. -Enemies of Pearl industries: -Polychaetes, barnacles, star fishes, etc. damage the shells. -Predatory fishes (Eels, Sorranids, Molluscs like Octopus, Sepia, Arthropods like Crabs, Lobsters, etc. are the natural enemies.