Effects of Saccharina japonica enzymatic hydrolysis extract on the growth and hepatopancreas transcriptome of Ictalurus punctatus

The aim of this study was to investigate the effects of kelp enzymatic extract on the growth and hepatopancreas transcriptome of Ictalurus punctatus. We prepared different diets with enzymatic extract of kelp addition amount of 0 g/kg (S), 0.3 g/kg (KP3), 0.5 g/kg (KP5), 1.0 g/kg (KP10), 1.5 g/kg (KP15), 2.0 g/kg (KP20) to feed channel catfish in cage-culture for 60 days. Channel catfish initial body weight (51.18±1.14)g as exprimental object were randomly divided into 6 groups with 3 replicates per group and 40 individuals per replicate. The results showed that: ① Compared with the control group S, the addition of kelp enzymatic extract in diet had no significant effect on the suvival rate(SR) of channel catfish, the specific growth rate(SGR) increased by 1.20% to 5.39%, and the feed coefficient rate(FCR) decreased by −0.83% to 9.09%. A quadratic polynomial regression analysis was carried out with SGR and FCR as the targets respectively, and the optimal addition amount of kelp enzymatic hydrolysis extract in the feed was 0.98 and 0.96 g/kg. The condition factor(CF) and viscero-somatic index(VSI) decreased significantly in groups KP10 to KP20, and the hepatosomatic index(HSI) decreased significantly in group KP10. The moisture, crude fat, crude protein and ash of fish had no significantly difference in all groups. ② Height of duplicature in group KP3, height and width of duplicature and thickness of muscularis in group KP5, thickness of muscularis in group KP10 were all significantly higher than those in group S. ③ Total RNA was extracted from S and KP10 groups’ hepatopancreas. Transcriptome sequencing results showed that there were 81 significantly down-regulated genes and 199 up-regulated genes. GO functional classification analysis results indicated that differentially expressed genes(DEGs) were annotated to items such as DNA transcription, metal ion binding, membrane and membrane composition. According to the results of KEGG pathway analysis, we found that DEGs were mainly enriched in 12 related pathways including cell proliferation and differentiation, hormone regulation, lipid metabolism, carbohydrate metabolism, growth factor metabolism and so on. Our studies have indicated that adding kelp enzymatic extract to diet can promote the growth of I. punctatus, reduce feed coefficient, and have positive effects on the intestinal morphology and the glucose and lipid metabolic capability of liver and pancreas. The suitable addition amount was 0.96-0.98 g/kg.