DIETARY EFFECTS OF ALGAL MEAL (Schizochytrium sp.) ON LIPID METABOLISM AND OXIDATIVE STRESS ENZYMES ACTIVITY IN SHRIMP (Litopenaeus vannamei)

Micro-algae are primary producers of omega-3 fatty acids, and algal-meal made from Schizochytrium sp., is rich source of docosahexaenoic acid, DHA. Currently, pacific white shrimp, Litopenaeus vannamei, is the most valuable single aquaculture commodity. The present study conducted a 12-week feeding trial to investigate the potential of replacing fish oil with algal-meal (65% lipid, 27% of which is DHA) in practical diets of pacific white shrimp (Litopenaeus vannamei), and its effects on the growth, antioxidant enzymes activity and fatty acids level, with the ultimate effects on sustainable shrimp production. For this purpose, three aquaria (110-L per aquarium) were randomly arranged and assigned to each experimental diet. 600-juvenile shrimp (average initial weight, 3.15 g) were fed with 8 iso-nitrogenous (38% protein), iso-lipidic (8% lipid), and iso-energetic diets: a control diet (Diet 1) containing 25% fishmeal (FM), 40% soybean meal, and 6% fish oil (FO) as a reference diet; and FO of diets 2-7 were replaced partially or completely with different combinations of linseed oil (LO), soy oil (SO), and AL-G Rich (Schizochytrium sp.) algal-meal (AO). FO and plant-based oil in Diet 8 were completely replaced with AO (Table 1).

At the end of the feeding trial, the results indicated that no significant differences were found for parameters such as growth and feed utilization ((body mass gain (BMG), specific growth rate (SGR), and feed conversion ratio (FCR)), total hepatic cholesterol malondialdehyde and fatty acids among treatments (Figure 1).

Dietary treatment did not affect survival rate (85 - 99%). However, fish oil replacements by algae meal influenced the activities of enzymes ((catalase (CAT), superoxide dismutase (SOD) and lipase (LIP)), and levels of adipocytes and muscle fatty acids (palmitoleic acid, oleic acid, linoleic acid, linolenic acid, EPA, eicosenoic acid, DHA, and palmitic acid) in shrimp. Notably, significant health-related functions (related to antioxidant and fatty acids capacity) were observed in the group fed Diet 6 (a combination of AO and LO) compared to others, complete replacement of FO with AO. The high level of LO in Diet 6 have produced high EPA in shrimp muscle (Figure 1).

In conclusion, algal-meal made from Schizochytrium sp., can totally replace fish oil in shrimp practical diets, without compromising the growth, survival and health of shrimp. This study is fundamental in developing cost-effective, nutritionally balanced and environment-friendly shrimp feed.