Breeding of Asian seabass pdf

Breeding of Asian seabass

13.1. Distribution and importance

• L. calcarifer belongs to the family Centropomidae and Order Perciformes.
• Good export market, esteemed fish in West Bengal.
• But carnivorous and highly predatory, cannibalistic when food is scarce.
• Grows to 300- 400 g in 3-4 months and 700-1200 g in 8-12 months. Maximum size recorded is 200 cm.
• Spends the growing phase in shallow brackish-water, estuaries and rivers.

Identifying characters

• Elongate and compressed body, with a deep caudal peduncle.
• Head is pointed with a concave dorsal profile , becoming convex in front of the dorsal fin.
• Mouth large, slightly oblique and the lower edge of the pre-opercle is serrated, with a strong spine.
• Adults are greenish or bluish above and silvery below.
• Eyes are bright pink, glowing at night.

Food and feeding

• Highly predatory, adult feeding on small fish and crustaceans.
• Juveniles are omnivorous.
• Fry feed on zooplankton, while fingerlings prefer small crustaceans, worms, mollusks, etc.

Breeding season

• Breeds during April – August, migrates to deeper waters for breeding.
• It is a protandrous hermaphrodite (functions first as male and then turns to female after spawning, i.e. natural sex-reversal).
• Fish in the weight range 2 – 3.5 kg are males, whereas those in the size range 3.5 – 5.0 kg are females.
• Three to four year-old fish show 1:1 (M:F) sex ratio.
• Males mature at 25 cm length.

13.2. Brood-stock development

• CIBA, Chennai has developed a technique for brood-stock development, breeding and larval rearing of L. calcarifer in India.
• Maturing fish (2-7 kg) collected from fishermen is stocked in 100 ton capacity concrete tanks with clean running water pumped from sea (sand-filtered).
• Water exchange at 70% daily
• Optimum salinity 28-32 ppt
• Fed with trash fish (live/fresh/frozen) like tilapia, sadines, anchovies, etc.
• Feeding rate 5%
• Prophylactic treatment with 100 ppm formalin to control parasites.
• Water quality monitored regularly

13.3. Spawning induction

• Attains maturity in captivity, but doesnot spawn naturally
• Females with >0.45 mm ova-diameter selected for induced breeding
• Females are implanted with LH-RH at 60-70 µg/kg
• Males without milt are implanted with LH-RH (30 µg/kg) and 17 α–MT pellet
• Females respond to the hormone 30-35 hours after implantation
• Ripe females ooze ova with pressure on abdomen and have swollen abdomen and anal region.
• Males ooze out milt with a slight pressure on abdomen and have anal region with thicker scales
• Males are stripped first and milt stored up to 4-5 days.
• Females are stripped off their eggs and fertilized with stored milt using dry method of fertilization.
• Intermittent spawner and releases eggs in batches over a period of 2-5 days.
• Diameter of fertilized eggs : 0.8-0.85 mm
• Fecundity : 2-17 million/kg b.w.
• Fertilized eggs are pelagic and transparent
• Hatching period : 17-18 hours at 29-31^oC.
• Eggs are hatched in 500 l capacity conico-cylindrical tanks at 100-200 eggs/l.
• Larvae depend on yolk for 3 days

13.4. Larval rearing

• The hatchlings (1.2-1.4 mm) are transferred 2-4 ton capacity tanks and reared at 30-50 nos./l
• Rotifer (Brachionus plicatilis) is given from 3^rd day at 20-30 nos./l, with 40% water exchange daily
• Artemia nauplii (2,000-3,000/l) and the rotifer are given during 11^th -15^th day
• Only Artemia (4,000-6,000/l) during 16^th-25^th day

The larvae reach 1-1.5 cm after 25-30 days when they are transferred to outdoor nursery tanks