Coastal Aquaculture and Mariculture (2+1)

Unit 5 - Finfish culture systems

5.3.2. Grow-out culture

• Asian sea bass has been cultivated for many years in brackish-water ponds. In recent years floating cages are used for production of marketable sized fish.
• The main problems of grow-out as earlier told is cannibalism and feeding, since this fish is highly predatory. Therefore grow-out is performed in two phases.
• In the first phase fry are grown to a weight of about 20 g in special nursery type of ponds of upto 2000m².
• Fry are stocked at the rate of 20-30/m².
• Besides natural food produced by fertilization, the fry are fed with supplementary feed consisting of ground trash fish twice a day.
• Exchange of water @ 30% per day is maintained. They are reared for a period of 30 – 40 days.
• By frequent sorting fingerlings of similar size are separated and stocked in separate grow out facilities for growing to market size.
  
• Grow-out period last for 3-4 months in countries like the Philippines, where 300-400g fish are acceptable and 8-2 months in other countries where marketable sized fish is 700g to 1.2 Kg.
• Floating and stationary cages of different sizes (usually 50m²) are used. The stocking density in cages is 40-50 fish /m³, after a growth of about 3 months is stock is thinned out to 10-20/m³.
• Fish are fed chopped trash fish or pelleted feed specially formulated for Asian sea bass. They are fed @ 10% of the biomass twice daily for two months after which it is reduced to 5% once a day.
• Weekly size grading is and full and frequent feeding is necessary until fish reach 15cm in length to avoid cannibalism.
• In ponds both mono- and polyculture is practices.
• In poly culture fish are reared with forage fish such as tilapias in the ratio of 1:20. The ponds are first stocked with the forage fish which reproduce rapidly and produce fry and fingerlings as food for the sea bass. When sufficient food is produced sea bass juveniles are stocked at a rate of 3000 to5000 per ha.
• In monoculture system sea bass juveniles are stocked at 10,000 to 20000 per ha with artificial feeding.
• Intensive culture of sea bass has proved to be economical and a production of about 3-3.5 tonnes can be obtained.
• The stocked fish in ponds grows to 500g in 6 months; 800 g in one year and to 3 Kg in one and half to two years. When stocked in freshwater reservoirs the fish is reported to have grown to 10 Kg size in three years in Australia.