Effects of soybean meal on immunity and transcriptomics of liver in pearl gentian grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

Soybean meal-induced enteritis (SBMIE) in fish is often accompanied by liver damage. However, the targeted analysis of liver has rarely been reported. This study mainly investigated the hepatic immune response of fish with SBMIE. Seven hundred and twenty pearl gentian groupers (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂) were fed one of the following three diets: 1) 50 % fish meal (FM); 2) soybean meal instead of 20 % fish meal (SBM20); and 3) dietary substitution up to 40 % (SBM40). Each treatment included four 1 m3 tanks. Each tank carried 60 fish. The initial weight of the fish ranged from 12.05 g to 12.60 g. The fish were sampled after 10 weeks of culture. Exposure to feeds containing 20 % and 40 % soybean meal had a negative impact on fish development and hepatic morphology. The hepatic inflammation and immune defects were apparent at the biochemical level based on indicators, such as Try, MDA, IgM, T-SOD, C3, C4, GR, and GSH-Px. The results of "3 + 2" full-length RNA-Seq showed that Th1 and Th2 cell differentiation played a key role in the hepatic immune system of grouper with SBMIE. The levels of cytokines, such as IFNγ, CSF, and TNFα, secreted by Th1 cells, were higher than those secreted by Th2 cells, including IL4, IL5, IL10, and TGFβ1. These variations in pro- and anti-inflammatory gene expression were also revealed by the results of RT-qPCR. The findings provide a valuable theoretical reference for the study of liver health, especially liver immune response in groupers with SBMIE.