Abstract
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.
Highlights
Litopenaeus vannamei was introduced to China in 1988 and rapidly became the most common shrimp species cultured in China
These alternative sources usually lack highly unsaturated fatty acids (HUFAs), especially docosahexaenoic acid (DHA), which is considered essential for the appropriate growth and survival of L. vannamei [7] because it cannot be synthesized de novo by this species
The final body weight gain and SGR peaked at 40% dried Schizochytrium (p < 0.05), and as the content of dried algae in the diet was further increased to 60%, the final body weight gain and SGR decreased
Summary
Litopenaeus vannamei was introduced to China in 1988 and rapidly became the most common shrimp species cultured in China. Numerous studies have evaluated the potential use of specific protein or lipid sources as alternatives to fish meals and fish oil in aquatic feeds [3,4,5,6]. These alternative sources usually lack HUFAs, especially docosahexaenoic acid (DHA), which is considered essential for the appropriate growth and survival of L. vannamei [7] because it cannot be synthesized de novo by this species. In addition to fish oil and fish meal, another potential option that has been explored as a source of DHA in aquaculture feeds is the use of heterotrophic microalgae, such as Schizochytrium sp. The objective of this study was to test the growth performance, digestive enzyme activity and serum biochemical composition of late postlarval L. vannamei fed diets containing various levels of Schizochytrium sp. fermentation products as the primary lipid and DHA source
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