The effect of oxidized fish oil on antioxidant ability, histology and transcriptome in intestine of the juvenile hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ Epinephelus lanceolatus)

Abstract

Fish oil is an important source of lipid in aquafeeds, but is prone to oxidation. In aquatic species, oxidized fish oil may induce oxidative stress. Although the intestine is an essential nutritional and immunological organ in juvenile hybrid grouper (Epinephelus fuscoguttatus × Epinephelus lanceolatus), the cause of its oxidative stress remains unknown. In the current research, a 65-day rearing experiment with diets containing 0% (R), 3% (L), 6% (M), or 9% (H) oxidized fish oil was conducted to explore the effects of oxidized fish oil on the antioxidant ability, histology, and transcriptome of the intestine in juvenile hybrid grouper. The concentrations of vitamin E and antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) in the foregut, midgut, and hindgut decreased significantly with the level of oxidized fish oil in the diet rose, whereas malondialdehyde (MDA) concentration increased. The oxidative stress damaged intestinal tissue structure. In detail, the goblet cell in H group was significantly reduced and the microvilli was depauperated. Compared with group R, the oxidized stress altered the intestinal transcriptome map in H group. A total of 29,360 unigenes had been annotated in all databases. There were 18 differentially expressed genes (DEGs), with 12 being up-regulated and 6 being down-regulated. According to the GO enrichment, the functions of differential genes were mostly enriched in primary metabolic process, cellular biosynthetic process, organic substance biosynthetic process, cellular macromolecule metabolic process, and protein metabolic process. There were 2 significant pathways including sulfur metabolism pathways and p53 signaling pathways involving cytochrome c (Cyt2c) gene with a high expression state under oxidative stress. In summary, oxidized fish oil induced intestinal oxidative stress. Meanwhile, oxidative stress was destroying the structure of the gut tissue. Furthermore, oxidative stress altered the intestinal transcriptome map.