EFFECTS OF DIET ARY N-3 HIGH LY UNSATURATED FATTY ACIDS ON GROWTH AND FATTY ACID COMPOSITION OF JUVENILE COBIA ( RACHYCENTRON CANADUM)

A feeding experiment was conducted in floating sea cages (1.0m× 1.5m× 2.0m) to determine the requirement of juvenile cobia ( Rachycentron canadum) for n-3 highly unsaturated fatty acids (n-3 HUFA). Six semi-purified diets were formulated to contain graded levels of n-3 HUFA, ranging from 0.6 to 2.11 %. Juvenile fish (weighing 8.3 ± 0.5g) were randomly divided into 18 cages of 20 fish, and fed one of 6 diets for 8 weeks. The water temperature fluctuated from 29 to 23. 5 ℃, the salinity from20.9 to 23.9 ‰, and dissolved oxygen content was approximately 7mg/L during the experimental period. No significant differences (ANOVA, p> 0. 05) in survival were observed among dietary treatments. However, specific growth rate (SGR) was significantly (p< 0.05) affected by dietary n-3 HUFA. SGR significantly increased with increasing dietary n-3 HU2 FA from 0 to 1124 %, and reached a peak at 1.56 % of n-3 HUFA. Then, SGR slightly decreased for the groups fed the diets containing higher than 1.56 % of n-3 HUFA. The content of 18∶ 1n-9 in muscle and liver decreased, while 22∶ 6 n-3 increased with increasing dietary n-3 HUFA. Based on SGR, the requirement for n-3 HUFA of juvenile cobia is about 1.49 % of dry dietby broken-line analysis.