Seed production of Asian catfish, Clarias batrachus

INTRODUCTION Cultured mainly in Thailand, Bangladesh and India. An important foodfish, commands high price (up to Rs. 200/-per kg) depending on local preference The catfishes of commercial/aquacultural importance are : Asian catfish, Clarias batrachus, African catfish, Clarias gariepinus, European catfish, Silurus glanis, American catfish, Ictalurus spp., Thai catfish, Pangasius hypothalamus, etc

Clarias batrachus Clarias gariepinus Silurus glanis Pangasius hypothalamus

Distribution and importance of C. batrachus C. batrachus belongs to the family Claridae and Order Cypriniformes. Also known as `Magur or walking catfish’, it is distributed in India, Bangladesh, Thailand, etc. Found in derelict water bodies like swamps, marshes and ponds and tanks. Can be cultured in oxygen-poor waters, as it is an air-breathing fish importance. An important food fish in North-eastern States such as Assam, West Bengal, Orissa, Bihar, etc. But carnivorous and cannibalistic when food is scarce. Grows to 200 g in 6-8 months

Identifying characters: Elongated body, Head moderately depressed Mouth terminal; Barbels four pairs; the maxillary pair extends considerably beyond base of pectoral fin while the nasal barbells extend to gill openings Dorsal fin inserted slightly anterior to tip of pectoral fins Pectoral spine strong, finely serrated on both sides. Adults are dingy-greenish or brownish superiorly, becoming lighter beneath; the vertical fins usually with reddish margins

Food and feeding: Adults are carnivorous and cannibalistic when food is scarce Juveniles are omnivorous Fry feed on zooplankton, while fingerlings prefer small crustaceans, worms, mollusks, etc

Brood-stock development: Broodfish is maintained in cement cisterns with a layer of soil and running water. Stocking density is 8,000 nos. /ha Fed with a mixture of ground trash fish and rice bran (9:1) Fish meal, wheat flour and soya cake can also be used in the diet Feeding rate 10% b.w. daily

Selection of broodfish for injection Proper selection of broodfish is important for successful results Attains maturity after one year (150 g and above) Sex of broodfish is identified based on secondary sexual characteristics which are more pronounced during breeding season. Females are slightly larger and have round and blunt genital papilla Males are slightly smaller and have elongated and pointed genital papilla Breeds naturally during April-July in paddy fields

Induced spawning: Hormone Dosage Female Male   1. Pituitary 20-30 mg/kg 1/3 dose 2. HCG 4,000 IU/kg 1/3 dose 3. Ovaprim 0.5 – 0.6 ml/kg 0.25 ml 4. Ovatide 0.6 – 0.7 ml/kg 0.30 ml 5. WOVA-FH 0.6 – 0.9 ml/kg 0.2-0.4 ml

Stripping and fertilization: At 14-16 hours after the injection, the male sacrificed, the testes dissected out and squashed in 0.9% NaCl solution. This sperm suspension can remain dormant (fertile) up to 24 hours. After the sperm suspension is ready, the eggs are stripped onto a clean basin/tray and are immediately fertilized with the sperms (suspension) The developing eggs are small, adhesive and are incubated in plastid basins (12 cm diameter x 6 cm high) with running water

Fecundity : 5,000 – 50,000 eggs/female Fertilization rate : 80 – 90% Unfertilized eggs get washed away by overflowing water Hatching period : 24-26 hours at 29-31 C. Eggs are hatched in 500 l capacity plastic/FRP tanks Larvae depend on yolk for 3-4 days

Larval rearing:  The hatchlings (5-5.5 mm) reared on Artemia nauplii or sieved zooplankton for 4-7 days, after which they are fed with egg yolk/white suspension for 8-15 days. The aerial respiration starts after 10 or 11 days. Water exchange 50-60% daily; aged water preferred Fingerlings are reared in out-door tanks where they are fed with ground trash fish and rice bran (1:1); stocking density : 200 nos./m2 Prawn or molluscan meat can also be used Attain 6-8 cm in 30 days and are ready for transfer to grow-out pond.