Evaluating the Impact of Arginine-to-Lysine Ratios on Growth Performance, Antioxidant Defense, and Immune Modulation in Juvenile Largemouth Bass (<i>Micropterus salmoides</i>)

This study examines the impact of the arginine/lysine ratio in feed on the growth, serum amino acids, arginine metabolism, and antioxidant capacity of juvenile largemouth bass (5.95 ± 0.02 g). Five isonitrogenous and isolipidic diets with varying arginine/lysine ratios were formulated and administered over an eight-week period. The results indicated that the treatments had no significant effect on protein efficiency ratio (PER), daily feed intake (DFI), or morphological indices of juvenile largemouth bass (<i>p</i> > 0.05). When the arginine/lysine ratio was 0.85 (2.25/2.65; 2.54/3.00), liver antioxidant capacity was maximized, and inflammatory factors were suppressed. Conversely, a ratio of 2.25/2.99 significantly reduced weight gain (WG) and specific growth rate (SGR) in juvenile largemouth bass, inhibited arginase activity, and increased serum total nitric oxide synthase (T-NOS) activity. When lysine was in excess (2.25/2.99 group), elevating arginine content (2.54/3.00 group) enhanced growth, antioxidant, and immune performance. Analysis of glutathione metabolism and innate immune-related pathway revealed that an optimal arginine/lysine ratio mitigates inflammatory damage induced by oxidative stress. An arginine/lysine imbalance significantly elevated liver malondialdehyde (MDA) content while reducing total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT) activities, and glutathione (GSH) content, thereby increasing the expression levels of inflammatory factors (<i>IL1B</i>, <i>IL8</i>, <i>TGFB1</i>, <i>BAX</i>). These findings demonstrate that an imbalance in arginine/lysine adversely affects the growth, metabolism, and antioxidant capacity of largemouth bass. When lysine is in excess, increasing the arginine content to achieve an arginine/lysine ratio of 0.85 alleviates the negative effects of antagonism, suggesting arginine supplementation may regulate oxidative damage caused by lysine excess.