Glutamate Supplementation Ameliorated Growth Impairment and Intestinal Injury in High-Soya-Meal-Fed Epinephelus coioides

This research assessed the efficacy of glutamate (Glu) supplementation to feed in counteracting growth restriction and intestinal stress-induced injury in juvenile groupers (<i>Epinephelus coioides</i>; initial weight 15.11 ± 0.03 g). The study comprised five isonitrogenous and iso-lipidic diets: a fish-meal-based (FM) diet, a soya-meal-based (SBM) diet, and SBM diets containing varying Glu levels of 1.0% (G-1), 2.0% (G-2), or 3.0% (G-3). The trial employed a randomized design with five treatment groups. Each group was housed in triplicate aquariums and received assigned diets for 56 consecutive days. Supplementation with Glu resulted in dose-dependent enhancements in weight gain, specific growth rate, serum high-density lipoprotein cholesterol, intestinal superoxide dismutase activity, digestive enzyme activity (trypsin, lipase, amylase), amino acid metabolic enzyme activity (glutaminase, GLS; glutamine synthetase), and intestinal mRNA levels of <i>GLS</i>, <i>IL-10,</i> and <i>TGF-β1</i>. Maximal values of the G-3 diet were restored to the levels of the FM diet (<i>p</i> > 0.05). Serum total cholesterol, intestinal total antioxidant capacity, and catalase activity followed a similar increasing trend with Glu level, attaining maxima in diet G-3, yet these values remained markedly lower than those of the FM diet (<i>p</i> < 0.05). Conversely, intestinal malondialdehyde content and mRNA levels of genes <i>IL-8</i>, <i>IL-12</i>, <i>IL-1β</i>, and <i>TNF-α</i> exhibited a significant dose-dependent decrease, reaching minimal levels in diet G-3 that were restored to the levels of the FM diet (<i>p</i> > 0.05). The results above demonstrate that Glu addition enhances nutritional status and intestinal structural integrity by augmenting antioxidant and digestive capacity and mitigating inflammatory responses, consequently enhancing growth performance and intestinal health.