Effect of Stocking Density on Aquaculture of Trachinotus ovatus in Off-shore Cage

Key words: 
• Trachinotu ovatus /
• survival rate /
• stocking density /
• profit margin /
• aquaculture cost

Abstract: Trachinotus ovatus was cultured at 5 stocking densities,e. g. 40,45,50,55,60 fishes/cubic meters in the HDPE circular double-buoy anti-wave net cages 60 m long in perimeter in the anti-wave net cage aquaculture sites around the waters of Houshuiwan Gulf,Lingao,Hainan,China to study the effect of stocking density on aquaculture of T. ovatus in the large net cage. The results showed that the influence of stocking density on survival rate and profit margin was not obvious in the density range of 40-50 fish ·m^-3（ p ＞ 0. 05）. At this density range T. ovatus had a survival rate of more than 80% and a profit margin of above 45%. The feed coefficient increased with the stocking density,and was the highest（ 1. 93） in the 60 fish·m^-3group and the lowest（ 1. 72） in the 40 fish·m^-3group. The percentage of Grade A fish decreased with an increase in stocking density but that of the fish in Grades B,C increased. The cost of the fish farming at the range of 40-50 fish·m^-3decreased with an increase in stocking density（ P ＜ 0. 05） and then tended to increase（ P ＜ 0. 01） at higher stocking densities,the highest cost being in the 60 fish·m^-3group( 18. 08 yuan·kg^-1) and the lowest being in the 50 fish·m^-3group( 16. 43yuan·kg^-1). The profits of the fish aquaculture increased with the stocking density at the stocking density range of 40-50 fish·m^-3（ P ＜ 0. 01） but decreased rapidly with the stocking density at the range of 50-60 fish·m^-3（ P ＜ 0. 01）. The highest profit was in the stocking density of 50 fish·m^-3( 185. 49 yuan·kg^-1) and the lowest in the stocking density of 60 fish·m^-3( 123. 85 yuan·kg^-1). It is hence recommended to farm T. ovatus at the stocking density range of 45-50 fishs·m^-3to produce optimal economic returns and less risk in fish aquaculture.