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

## TL;DR

This study shows that the right balance of arginine and lysine in fish feed improves growth and reduces stress in juvenile largemouth bass.

## Contribution

The study identifies an optimal arginine-to-lysine ratio (0.85) that enhances antioxidant defenses and mitigates lysine-induced stress in largemouth bass.

## Key findings

- An arginine/lysine ratio of 0.85 maximized liver antioxidant capacity and suppressed inflammation in juvenile largemouth bass.
- Excess lysine impaired growth and increased oxidative stress, but adding more arginine reversed these negative effects.
- Imbalanced ratios elevated liver MDA and inflammatory markers, highlighting the importance of amino acid balance in aquaculture.

## Abstract

Optimal nutrition, particularly a balanced ratio of arginine to lysine, is critical for the healthy growth of juvenile largemouth bass. This study investigated the effects of varying dietary arginine-to-lysine ratios on growth performance, metabolism, and antioxidant capacity over an eight-week period. Results indicated that an arginine-to-lysine ratio of 0.85 enhanced hepatic antioxidant capacity and reduced inflammation. Conversely, excessive dietary lysine impaired growth, disrupted metabolic homeostasis, and increased oxidative stress. Supplementation with arginine under lysine-excess conditions improved growth, enhanced immunity, and bolstered antioxidant defenses, effectively mitigating the adverse effects of the amino acid imbalance. These findings suggest that maintaining an appropriate arginine-to-lysine ratio in aquaculture feed is essential for promoting growth and mitigating stress in juvenile largemouth bass, potentially leading to improvements in feed formulation.

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 (p > 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 (IL1B, IL8, TGFB1, BAX). 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.