Effects of Dietary Leucine Levels on Growth Performance and Muscle Quality in Oriental River Prawn (Macrobrachium nipponense)

This investigation assessed how varying dietary leucine concentrations impact the growth performance, antioxidant status, and muscle quality of the oriental river prawn (Macrobrachium nipponense). Six isonitrogenous and iso-lipidic diets containing incremental leucine levels (0.76%, 1.16%, 1.48%, 1.94%, 2.32%, 2.74%) were fed to prawns over 8 weeks. Dietary leucine significantly affected measured growth indices (p < 0.05). Based on the broken-line regression model of specific growth rate (SGR) and protein deposition rate (PDR), the optimal dietary leucine levels were 2.36% and 2.34%, corresponding to 6.45% and 6.39% of crude protein. Crude protein and muscle leucine contents peaked at the 2.32% leucine level, significantly exceeding those in the 1.16% group (p < 0.05). Hepatopancreatic lipase (LPS) activity and total antioxidant capacity (T-AOC) were significantly elevated in the 2.74% group relative to the control (p < 0.05). Dietary leucine levels significantly affected superoxide dismutase (SOD) and malondialdehyde (MDA) (p < 0.05); the maximum SOD activity was observed in the 1.94% group, while the minimum MDA level was observed in the 2.32% group. Drip loss was significantly reduced by dietary leucine supplementation (p < 0.05). Dietary leucine significantly affected gene expression related to protein and muscle synthesis in muscle (p < 0.05). Relative mRNA levels of tor and s6k1 were significantly elevated in the 2.32% and 2.74% groups compared with the control (p < 0.05), while myf5 expression peaked at 2.74% leucine (p < 0.05). Conversely, mstn expression was significantly downregulated at 2.32% leucine relative to the 1.16% group (p < 0.05). These results demonstrate that an appropriate dietary leucine level can promote prawn growth, enhance antioxidant defense capacity, and improve muscle quality.