Abstract:A 70-day trial was conducted to investigate the effect of replacement of dietary fish meal by Nannochloropsis sp. meal on growth performance, body composition, and serum biochemical indices of juvenile turbot Scophthalmus maximus L. with an initial weight body weight of (24.60±0.02) g. Five isonitrogenous and isoenergetic diets (N0, N3.88, N7.76, N11.64, and N15.52) were formulated with 0%, 3.88%, 7.76%, 11.64%, and 15.52% fish meal replaced by Nannochloropsis sp. meal, respectively. Each diet was randomly fed to three replicates of fish, with 40 fish per replicate. The following results were obtained. 1) There were no significant differences (P>0.05) in weight growth rate, specific growth rate, protein efficiency ratio, feed coefficient ratio, feed intake, condition factor, and survival rate among the groups. 2) As the meal content of Nannochloropsis sp. increased, the crude lipid content in the whole body and muscle was significantly decreased (P<0.05); however the crude protein, crude ash, and moisture content were not significantly different (P>0.05). 3) Lysozyme, complement protein C3, complement protein C4, and acid phosphatase activities showed a rising trend followed by a decline, with the highest point reached in the N7.76, N7.76, N11.64, and N7.76 groups, respectively, and were significantly higher than that in the N0 group (P<0.05). The alkaline phosphatase activity of the N15.52 group was significantly lower than that the other groups and there were no significant differences among other groups (P>0.05). 4) The total superoxide dismutase, total antioxidant capacity, and glutathione peroxidase activities in the serum of the algae meal groups first increased and then decreased, and reached a maximum in the N7.76 group, which was significantly higher than that in the N0 group (P<0.05). 5) The triglyceride content in the serum of the N7.76 group was significantly lower than that in the other groups (P<0.05), and there were no significant differences among the other groups (P>0.05). The total cholesterol content of the algae meal groups was significantly lower than in the N0 group (P<0.05), but there were no significantly differences among the algae meal groups. 6) The aspartate aminotransferase activity in the serum of the algae meal groups followed a decreasing to increasing trend, reaching the lowest point in the N11.64 group and was significantly lower than that in the N0 group (P<0.05). The alanine aminotransferase activity of the algae meal groups was significantly lower than that in the N0 group (P<0.05). In conclusion, under the experimental conditions tested, Nannochloropsis sp. meal could replace 15.52% of fish meal in juvenile turbot feed without any effects on the growth performance, and the replacement of 7.76% fish meal significantly improved the nonspecific immunity and reduced the blood lipid levels in juvenile turbot.
