Histology and transcriptomic analysis reveal effects of dietary fish oil and soybean oil on lipid absorption and immune inflammation in the foregut of adult female spotted scat (Scatophagus argus)

Abstract

The foregut is the main site of lipid absorption in fish, but the effect of different lipid sources on the foregut lipid absorption and metabolism in adult female spotted scat is still unclear. In this experiment, adult female spotted scat (length = 19.48 ± 1.13 cm, weight = 242.83 ± 50.90 g) were fed two iso-nitrogenous (45 % crude protein) and iso-lipidic (12.5 % crude lipid) diets configured with either 8 % fish oil (FO) or 8 % soybean oil (SO) for 60 days. Histological observations, serum measurements and transcriptome sequencing were used to investigate the effects of the oil sources on the foregut. Histological observation showed that the foregut folds of the SO group were shorter and narrower than those of the FO group, and nuclear vacuolation and villous atrophy were observed in the intestinal cells of fish in the SO group, indicating an inflammatory reaction. Both serum triglyceride and total cholesterol levels were significantly higher in the FO group than in the SO group. Transcriptome analysis revealed 1355 differentially expressed genes between the FO and SO groups. Genes related to lipid metabolism (adipor2 and creb3l3) and cholesterol absorption and efflux (npc1l1 and sphk2) were up-regulated, whereas genes related to fatty acid synthesis and transport (fad1 and mfsd2ab) were down-regulated in the FO group. Circadian rhythm related genes ciart and nfil3, which are also involved in lipid metabolism, were up- and down-regulated, respectively in the FO group. The immune-related genes steap4, ddit4 and cldn6 which can inhibit inflammation, were up-regulated in the FO group, whereas pro-inflammation gene rnf225 was up-regulated in the SO group. In conclusion, compared with SO, FO may enhance the lipid absorption and reduce the inflammatory response in the foregut of the spotted scat. The results of this study provide a reference for the selection of dietary oil sources for adult female spotted scat.