L-glutamine plus L-glutamic acid enhances growth performance, ammonia detoxification, gut bacteriome and expression of anti-inflammatory cytokine IL-10 in Nile tilapia fingerlings

This study aimed to evaluate the effects of dietary glutamine (Gln) and glutamic acid (Glu) blend on growth performance, plasmatic biochemical parameters, intestinal bacteriome composition, short-chain fatty acids (SCFAs) production, digestive enzyme activity, and histomorphometry of Nile tilapia fingerlings. The study also aimed to evaluate the effects of this blend on liver antioxidant status and gene expression of anti-inflammatory interleukin 10 (IL-10), pre-inflammatory interleukin 1β (IL-1β), glutamine synthetase (GS), and peroxisome proliferator-activated receptor alpha (PPAR-α). Fish (n = 408; 1.0 ± 0.0 g) were randomly distributed into eight aquaria (51 fish each) and fed micro-extruded diets either unsupplemented (CON) or supplemented with 20 g kg^-1 of Gln and Glu (1:1) blend (AMG). Fish were hand-fed six times daily until apparent satiety for 30 days. Fish fed AMG diet showed higher body weight gain (+3.0 %) than those fed CON diet. Additionally, these fish exhibited a higher abundance of Staphylococcus saprophyticus, a SCFA-producing bacterium known for its probiotic-like potential in fish. Consequently, fish fed AMG diet exhibited higher intestinal butyric acid production and increased intestinal fold height relative to fish fed CON diet. The upregulation of PPAR-α and GS genes suggested that fish fed AMG diet exhibited improved energy metabolism and ammonia excretion, respectively. Furthermore, the upregulated expression of the anti-inflammatory cytokine IL-10 gene in fish fed AMG diet indicated enhanced immune responses. Fish fed AMG diet showed increased activity of superoxide dismutase and glutathione-S-transferase and decreased malondialdehyde concentration in the liver. Dietary supplementation with 20 g kg^-1 of Gln plus Glu promoted fish growth and survival through beneficial modulation of the bacteriome, improving intestinal health and function, supporting nutrient absorption and metabolism, strengthening innate immunity, and reducing oxidative stress in Nile tilapia fingerlings.