Optimizing valine supplementation in low-fish meal diets for enhanced growth, digestion, antioxidant capacity, and intestinal health of triploid rainbow trout (Oncorhynchus mykiss)

This study evaluates the effects of valine on the growth, digestion, antioxidant capacity, and intestinal health of triploid rainbow trout (Oncorhynchus mykiss) fed a low fish meal diet (10 %). The trouts with an initial body weight of 15.08±0.20 g were fed with five different isonitrogenous and isoenergetic diets containing levels of valine: 0.86 % (G1), 1.79 % (G2), 2.43 % (G3), 3.02 % (G4), and 3.68 % (G5) for 56 days. The results showed that the weight growth rate and specific growth rate of the 2.43 % group were significantly higher than those of the 0.86 % control group (P<0.05). The intestinal villus length and muscle layer thickness propria were significantly increased in the 3.02 % group compared to the control group (P<0.05). The activities of intestinal protease, amylase, superoxide dismutase, catalase, and lysozyme in the 2.43 % group were significantly higher than those in the control group (P<0.05). The levels of interleukin-8 and tumor necrosis factor-alpha were lowest in the 3.02 % group, while the IL-10 level was highest in the 3.02 % group (P<0.05). Elevated levels of valine in the dietary regimen correlated positively with the upregulation of pivotal genes associated with antioxidant mechanisms, notably nuclear factor erythroid 2-related factor 2 (Nrf2), NAD(P)H: quinone oxidoreductase 1 (NQO1), and thioredoxin (Trx). Additionally, the expression of genes implicated in the synthesis of tight junction proteins, including occludin, claudin 7b, and claudin 15, exhibited significant augmentation with escalating valine concentrations in the feed. In conclusion, dietary valine enhanced the growth, digestive and absorptive capabilities, antioxidant capacity, and intestinal health of O. mykiss. An analysis based on a quadratic curve model, which incorporates specific rates of growth and weight gain, establishes that the optimal dietary valine requirement for triploid O. mykiss consuming a 10 % fish meal diet ranges between 2.43 % and 2.69 %.