Growth performance, lipid metabolism, gut histoarchitecture and immune and antioxidant related gene expression in juvenile Asian sea bass, Lates calcarifer fed peroxidized lipids with or without dietary selenium nanoparticles

This study evaluated the effects of dietary recovered frying soybean oil (RFSBO) and selenium nanoparticles (SeNPs) on growth performance, hepatic metabolism, intestinal morphology, and the expression of antioxidant, immune, and growth-related genes in juvenile Asian sea bass (Lates calcarifer, 41.5 ± 0.1 g) reared under high temperature (32–33 °C) and high salinity (38–40 ppt). Six diets were formulated: fresh soybean oil (FSBO), FSBO + SN (4 mg/kg SeNPs), 50 % RFSBO, 50 % RFSBO + SN, 100 % RFSBO, and 100 % RFSBO + SN. Fish (n = 450) were randomly assigned to 18 tanks and fed to apparent satiation three times daily for eight weeks. Fish fed 50 % RFSBO + SN achieved similar final weights to the FSBO group but with significantly better feed conversion ratio, improved gut wall, epithelial, and villus height, and lower malic enzyme activity, indicating reduced metabolic stress. Hepatic triglycerides were significantly lower in this group than in FSBO-fed fish, while glycogen content was maintained. In contrast, 100 % RFSBO caused histological damage, oxidative stress, elevated isocitrate dehydrogenase activity, and lipid imbalance, with SeNPs offering only partial mitigation. SeNP supplementation upregulated gpx1, lyz, il-1β, and igf1 expression under moderate oxidative stress but had limited effects under severe conditions. Overall, RFSBO can replace up to 50 % of dietary FSBO without compromising growth or intestinal health when combined with SeNPs, but higher levels reduce SeNP efficacy. These findings support the use of moderate RFSBO inclusion with SeNP supplementation to sustain fish health and performance under challenging environmental conditions.