The effect of agavin on the intestinal antioxidant response and its relationship to gut microbiota and plasma cortisol in Nile tilapia (Oreochromis niloticus) subjected to overcrowding stress

Abstract

High-density aquaculture of Nile tilapia (Oreochromis niloticus) affects welfare by altering cortisol levels, antioxidant response (superoxide dismutase, catalase, and malondialdehyde), and gut microbiota. Agavin is a fructose- and glucose-based polysaccharide containing β-(2-1) and β-(2-6) linkages, known for its potential to mitigate the adverse effects of oxidative stress. This study evaluated the impact of agavin on the intestinal antioxidant response and investigated its correlation with gut microbiota composition and cortisol levels. Fish were fed a control diet (DC0, no agavin) or diets supplemented with 20 g kg⁻¹ (D20) or 40 g kg⁻¹ (D40) of agavin for 110 days. On day 90, all fish were subjected to high-density stress (63 kg m⁻³). Intestinal superoxide activity, catalase activity, and malondialdehyde concentrations were correlated with previously published plasma cortisol and microbiota data from the same study. Under high-density conditions, the D20 diet increased superoxide dismutase and catalase activity and reduced malondialdehyde concentration compared to the control. Plasma cortisol and malondialdehyde concentration showed a positive correlation (r = 0.67), but plasma cortisol was negatively correlated with superoxide dismutase activity (r = − 0.50). Sixty-nine and 81 operational taxonomic units (OTUs) were significantly correlated with catalase and superoxide dismutase activity, respectively, with families from the Order Cytophagales being strongly positively correlated. Cytophagales was also negatively correlated with plasma cortisol and malondialdehyde concentrations. These results suggest that, under stress conditions, agavin promotes the antioxidant response, modulating the intestinal microbiota and reducing cortisol release, which could indicate its utility as a prebiotic in aquaculture.