OPTIMIZING THE USE OF ALGAL MEAL Schizochytrium sp. AS A FISH OIL REPLACER IN THE PRACTICAL DIETS OF PACIFIC WHITE SHRIMP Litopenaeus vannamei  

Shrimp farming is booming, with worldwide aquaculture output growing faster than any other agricultural sector. The current trend to intensify shrimp farming is increasing interest in using alternative oil sources in the formulation of diets. Microalgae are primary producers of omega-3 fatty acids and algal meal made from Schizochytrium sp. is rich source of DHA. The overall goal of the present study was to examine 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), for sustainable shrimp production.

Shrimp juveniles (600; average weight 3.15 g) were randomly distributed and stocked into twenty-four 110-L glass aquaria (25 per tank^-1) in a closed recirculating system. Shrimp were fed eight experimental diets for 12 weeks. Feeding rates were adjusted according to satiation of the shrimp.

Eight diets were formulated isonitrogenous (38% protein), iso-lipidic (8% lipid), and isoenergetic. A control diet (Diet 1) was formulated containing 25% FM, 40% soybean meal (SBM), and 6% fish oil (FO) as a reference diet. Fish oil 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) (Table 1). Notably, FO in experimental Diet 8 was replaced completely with AO (Table 1).

There were no significant differences between body mass gain (BMG, %), specific growth rate (SGR, %.day^-1), feed conversion ratio (FCR), protein efficiency ratio (PER) values, glucose, albumin, globulin and total protein concentration in haemolymph of shrimp fed the various diets (Table 2). Survival rate ranged from 85 - 99%; and concentration of total bilirubin (1.33-2.65 mg/dl), creatinine (0.60-1.15 mg/dl) and urea nitrogen (3.33-4.33 mg/dl) in haemolymph were significantly similar for all treatment groups.

Fatty acids profiles of feed, muscle and hepatopancreas of shrimp; enzymes involved in lipid metabolism especially desaturase and elongase, and antioxidant enzymes are being analyzed and will be presented. Overall, the results of this research indicated that algae meal can replace fish oil without compromising the growth, survival and health of shrimp.  In conclusion, microalgae (Schizochytrium sp.) production of DHA has the potential to develop into a sustainable alternative to fish oil for use in shrimp feed.