Dietary additives have the potential to stimulate the whiteleg shrimp immune system, but information is scarce on their use in diets for larval/post-larval stages. The potential beneficial effects of vitamins C and E, β-glucans, taurine, and methionine were evaluated. Four experimental microdiets were tested: a positive control diet (PC); the PC with decreased levels of vitamin C and E as negative control (NC); the PC with increased taurine and methionine levels (T + M); and the PC supplemented with β-glucans (BG). No changes in growth performance and survival were observed. However, post-larvae shrimp fed the NC had lower relative expressions of pen-3 than those fed the PC, suggesting that lower levels of vitamins C and E may impact the shrimp immune status. Lipid peroxidation levels dropped significantly in the BG compared to the PC, indicating that β-glucans improved the post-larvae antioxidant mechanisms. Furthermore, when compared with the NC diet, PL fed with BG showed significant increases in tGSH levels and in the relative expression of crus and pen-3, suggesting a synergistic effect between vitamins C and E and β-glucans. Amongst the additives tested, β-glucans seems to be the most promising even when compared to a high-quality control diet.

This study evaluated the effects of different marine protein sources and dietary lipid levels in inert microdiets for whiteleg shrimp (Penaeus vannamei) post-larvae (PL) reared in clear-water recirculating aquaculture systems (RAS). Five diets were evaluated: a control diet containing a blend of fish and squid meals, diets based on fish meal, squid meal, or krill meal as the main marine ingredient, and a high-lipid fish meal-based formulation used to assess the effect of increased dietary lipid content. After 21 days, growth performance did not differ significantly among treatments. However, survival and physiological status were significantly affected by diet. PL fed the control and krill-based diets showed higher survival (76.5 and 78.0%, respectively), whereas survival was lowest with the high-lipid fish meal-based diet (41.5%), which also resulted in an increased feed conversion ratio (FCR). Fatty acid composition reflected dietary inputs, with higher levels of n-3 polyunsaturated fatty acids in PL fed the high-lipid diet. Biomarker and gene expression analyses revealed modulation of antioxidant and immune responses in PL fed single-ingredient diets and the high-lipid formulation, suggesting increased physiological stress compared to the control and krill-based treatments. These results show that growth alone is not sufficient to assess diet adequacy. The use of combined marine protein sources or krill meal was associated with higher survival, while increasing dietary lipid content from 14 to 16% did not improve growth performance and was associated with reduced survival.