Effect of dietary n-3/n-6 HUFA on growth performance, fatty acid composition of whole fish and serum biochemical indices in turbot (Scophthalmus maximus)

An 8-week feeding trial was conducted in a recirculated system to study the effect of dietary n-3/n-6 HUFA (D1: 29.54, D2: 23.04, D3: 18.97, D4: 9.06, D5: 6.86, D6: 3.87) on growth performance, the fatty acid composition of whole body and serum biochemical indices in turbot (Scophthalmus maximus). Six diets were formulated to feed six groups of juvenile turbot mean initial weight (12.18±0.01) g, respectively. Each diet was randomly fed to triplicate groups of 35 fish per tank. Results showed that dietary n-3/n-6 HUFA had no significant effect on the survival rate(SR) of turbot. With the decreasing of the dietary n-3/n-6 fatty acid ratios, the weight gain rate (WGR), protein efficiency ratio (PER) and specific growth rate (SGR) increased first, then decreased. And WGR, PER and SGR of D6 group was significantly lower than other groups. PER of D2 group was significantly higher than other groups. Crude protein and ash of whole body increased at the beginning and then decreased. Crude protein and ash of muscle of D6 group was remarkably lower than the others. The fatty acid composition analysis showed that the concentration of ARA increased with decreasing of dietary n-3/n-6 HUFA, while EPA, DHA, n-3/n-6 PUFA and n-3/n-6 HUFA content followed the opposite pattern. Acid phosphatase (ACP) and superoxide dismutase (SOD) were increased among dietary treatments. Serum lysozyme (LZM) activity increased with reducing dietary n-3/n-6 HUFA from 29.54 to 23.04, and decreased with further decrease of n-3/n-6 HUFA from 23.04 to 3.87. Total antioxidant capacity (T-AOC) showed a similar trend with serum lysozyme activity with the highest value in the ratio of 18.97, significantly higher than that in the control and ratio of 3.87 groups. These results suggested that dietary n-3/n-6 HUFA, especially moderate n-3/n-6 HUFA (18.97~23.04), enhanced growth and immune response and modified the chemical composition of whole body and muscle of juvenile turbot.