Protective effect of selenium supplementation against damage of health and muscle quality in Onychostoma macrolepis under a thermally oxidized fish oil–enriched diet

Abstract

Fish oil is rich in highly unsaturated fatty acids such as EPA and DHA, which are easily oxidized, while selenium is an essential micronutrient that contributes to antioxidant defense by forming selenoproteins involved in maintaining cellular homeostasis. In this study, to explore the effects of selenium (selenium-rich black bean dregs; SeB) on the growth, health status, and muscle quality of Onychostoma macrolepis (O. macrolepis) under a thermally oxidized fish oil–enriched diet, a total of 156 O. macrolepis (3.43 ± 0.25 g/fish) were divided into four groups (triplicate per group) and fed with four isonitrogenous (386.7 g/kg) and isolipidic (91.7 g/kg) diets: fresh fish oil (FFO), oxidized fish oil (OFO), oxidized fish oil supplemented with selenium (1.48 mg Se/kg diet; selenium-rich yeast; OFOSeY), and oxidized fish oil supplemented with selenium (1.48 mg Se/kg diet; selenium-rich black bean dregs; OFOSeB) respectively, in a recirculation aquaculture system for 60 days. The results showed that the HSI (hepatosomatic index) was the highest in the OFO group, and it significantly decreased in selenium supplementation groups (OFOSeB and OFOSeY; P < 0.05). The proximate composition, selenium content, and amino acid composition of the muscle in four groups were not significantly different (P > 0.05). The fatty acid content of 18:0, 18:1n-7, 20:3n-6, 20:5n-3, 22:5n-3, 22:6n-3, and n-3 PUFA were significantly reduced in the muscle of the OFO group compared to the FFO group (P < 0.05), and they were recovered in selenium supplementation groups (OFOSeB and OFOSeY; P < 0.05). The serum ALT (aspartate aminotransferase), TG (triglyceride), and MDA (malondialdehyde) were the highest in the OFO group, and they were recovered in selenium supplementation groups (OFOSeB and OFOSeY; P < 0.05). The structure of hepatocytes, intestine, muscle, and intraperitoneal adipocyte, including the hepatopancreas mitochondria, the intestinal villi, and muscle fibers showed abnormalities in the OFO group, and the supplementation of selenium (OFOSeB and OFOSeY) showed recovery. The abundance of the intestinal bacteria of the O. macrolepis was adversely affected by OFO (Proteobacteria significantly increased and Actinomycetes significantly decreased), and the supplementation of selenium recovered it to a healthier state. The relative gene expression of sod, gpx, and cat were not significantly different between FFO and OFO groups, while they significantly increased in the selenium supplementation group of OFOSeY (P < 0.05). The metabolomics results showed that there were significant differences in 23 metabolites between the OFO and OFOSeB groups (P < 0.05), which were significantly involved in the pathway of sphingolipid metabolism, histidine metabolism, fructose and mannose metabolism, and fatty acid biosynthesis (P < 0.05). In summary, the present results indicated the protective effect of selenium supplementation against injury to health in hepatopancreas, intestine, and muscle of O. macrolepis under a thermally oxidized fish oil–enriched diet, and this protective effect probably comes from the improvement of the antioxidant capacity, intensified by selenium, as it is a crucial component of antioxidant enzymes.