Effects of dietary n-3/n-6 HUFA on growth, body composition and fatty acid composition of tissue in juvenile rockfish (Sebastes schlegeli)

A 65 d feeding trial was conducted in a float cage to study the effect of dietary n-3/n-6 HUFA(D1:14.28, D2:9.26, D3:5.66, D4:3.06, D5:2.02, D6:1.50) on growth, body composition and fatty acid composition of tissue in juvenile rockfish (Sebastes schlegeli). Six diets were formulated to feed six groups of juvenile S. schlegeli mean initial weight (36.30±0.03) g, respectively. Each diet was randomly fed to triplicate groups of 30 fish per cage. The results show that: ①Dietary n-3/n-6 HUFA had no significant impact on the survival rate of fish (P>0.05).With the decreasing of dietary n-3/n-6 HUFA, the weight gain rate first increased and then decreased, the feed conversion ratio (FCR) showed an opposite trend, and the weight gain rate of D2 and D3 groups was significantly higher than that of other groups (P<0.05). ②The crude fat in the whole fish and muscle showed a trend of increased first and then decreased, which reaching their peaks in group D2 and D3, respectively(P<0.05).The crude fat in the liver first decreased and then increased, and the D2 group was significantly lower than the other groups (P<0.05).③ The content of C20:4n-6 in all tissues were increased with the decreasing of dietary n-3/n-6 HUFA. C20:5n-3, C22:6n-3 and n-3/n-6 HUFA in all tissues showed an overall decreased trend. ④The fatty acid composition of fish body was affected by the dietary, in order of abdominal fat, muscle, whole fish and liver. The dietary C20:4n-6 was negatively correlated with C20:5n-3 of all tissues. Under this experimental conditions, the appropriate proportion of dietary n-3/n-6HUFA (5.66-9.26) can significantly improve the growth of experimental fish, and modify body composition and fatty acid composition of tissues. The univariate quadratic regression analysis, based on weight gain rate and feed conversion ratio, showed that the appropriate proportion of n-3/n-6 HUFA in the dietary of juvenile S. schlegeli is 8.93 and 8.70, respectively.