Effect of Schizochytrium sp., on the Growth, Fatty Acid Composition, Digestive Enzyme and Serum Biochemical Composition of Postlarval Litopenaeus vannamei

In this study, shrimp feed was substituted with a dried alga, Schizochytrium sp., at five levels (0, 10, 20, 40, and 60% of compound feed) to yield protein/energy (P/E) ratios of 22.72, 19.75, 16.71, 13.72 and 10.75 mg protein/KJ, respectively. The effects of this substitution on the specific growth rate (SGR), survival rate, fatty acid composition, digestive enzyme activities and biochemical composition of the sera in postlarval white shrimp (Litopenaeus vannamei) were evaluated. Four replicates, each consisting of 5,000 postlarval shrimp in a single cage, were performed at each substitution level. The postlarval shrimp were randomly distributed to 20 cages, and the duration of the trial was 50 d. The results showed that the best performance was obtained with a diet containing 40% dried Schizochytrium. The survival rate of the 40% trial group was 24% higher than that of the shrimp fed a control diet (p < 0.05). The final body weight gain and SGR peaked at a substitution level of 40% dried Schizochytrium (p < 0.05). The feed conversion ratios (FCRs) of the 20% and 40% trial groups were significantly lower than that of the control group (p < 0.05). The muscle protein and ash contents of the shrimp fed diets containing 20% and 40% dried algae were higher than those of the shrimp fed the control diet (p < 0.05). Although the level of dried Schizochytrium was associated with a decrease in the protease specific activity, an increase in the lipase activity was observed. The serum biochemical composition of the shrimp was significantly affected by the level of dried Schizochytrium in the diet (p < 0.05). In summary, when the feed content of dried Schizochytrium ranged from 20 to 40%, an optimal P/E ratio of 13.72-16.71 mg protein/KJ was achieved. Thus, such supplementation could increase the amount of highly unsaturated fatty acids (HUFAs) and decrease the required level of protein in the production of high-quality feed.