Effects of enrichment of live prey with soy lecithin on growth, stress resistance, digestive enzymes activity, and antioxidant capacity in yellowfin seabream (<i>Acanthopagrus latus</i>) larvae

Phospholipid (PL) is an essential nutrient that has vital effects on growth, stress resistance, and early development in marine fish larvae. In this regard, a 30-day feeding experiment was conducted in order to examine the effects of live prey enrichment with graded levels of soy lecithin (SL) on some physiological responses of Acanthopagrus latus larvae. Four experimental emulsion levels of SL were used to enrich rotifer and Artemia including very low (2%, N-Nil), low (4%, L), medium (8%, M), and high (12%, H). Newly hatched larvae were distributed into 12,250-L cylindrical tanks with an initial density of 15,000 larvae in each tank that was supplied with natural seawater (23 ± 1°C; 40.0 ± 1.0 g L^-1). Larvae fed live prey enriched with 4% SL significantly had higher wet weight gain than other treatments. Air exposure and osmotic activity tests were also performed to detect larval resistance to stress. Larvae fed live prey enriched with 8% and 12% SL had higher survival compared to the other two groups. The accumulation of arachidonic (ARA) and docosahexaenoic acid (DHA) was increased in the whole body of larvae fed high SL-supplemented live prey. Alkaline phosphatase and aminopeptidase N activities in the guts brush border membrane of larvae in M and H groups were higher than other treatments. The trypsin and chymotrypsin activities in the N group were lower than in other groups. The highest and lowest amylase activities were in the H and N groups, respectively. The activity of catalase in the whole body of the M group was higher than the N group and the glutathione reductase activity was significantly increased in the M and L groups compared to the N and H groups. Total antioxidant capacity in the whole body of larvae in the N group was lower than in the other treatments. In summary, moderate levels of SL (4%-8%) are suggested for the enrichment of live prey in A. latus.