Soybean protein concentrate causes enteritis in juvenile pearl gentian groupers (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

Due to diminishing fish meal (FM) supplies, superb protein (PRO) sources are needed for aquaculture, such as soy-based PRO. However, these can cause enteritis and even intestinal injury in fish when used at high proportions in feed. This research examines the effects of substituting soybean protein concentrate (SPC) for FM on the growth performance and intestinal balance of pearl gentian groupers and investigates the mechanism of SPC-induced enteritis. Experimental fish (n = 720) were fed 1 of 3 following diets: (1) a 50% FM diet (control), (2) a diet with 20% of the FM substituted with SPC (group SPC20), and (3) a 40% SPC-substituted diet (SPC40). Fish were fed for 10 wk iso-nitrogenous (50% PRO) and iso-lipidic (10% lipid) diets. Groups SPC20 and SPC40 showed significantly lower developmental performance and intestinal structures than control. Group SPC40 had significantly higher expressions of pro-inflammatory-related genes, such as interleukin 1β (IL1β), IL12, IL17 and tumor necrosis factor α and significantly lower expressions of anti-inflammatory-related genes, such as IL5, IL10 and transforming growth factor β1. Biochemical and 16S high-throughput sequencing showed that the abundance and functions of intestinal flora in group SPC40 were significantly affected (P < 0.05), and there were significant correlations between operational taxonomic unit abundance variations and inflammatory gene expressions at genus level (P < 0.05). The second- and third-generation full-length transcriptome sequence was used to analyze the mechanism of SPC-induced enteritis in pearl gentian groupers, which showed that enteritis induced by SPC may be caused by disturbances to intestinal immune function induced by an imbalance in intestinal nutrition and metabolism, such as the intestinal immunity network for IgA production pathway. However, it remains unclear as to which intestinal immune or nutritional imbalance is most important in enteritis development. This study provides a basis for further research into soy PRO-related enteritis in fish.