Enteritis poses a significant threat to fish farming, causing intestinal and hepatic inflammation, physiological dysfunction, and dysbiosis. Our study focused on the leopard coral grouper (Plectropomus leopardus ) during an enteritis outbreak on a South China Sea farm. No abnormalities in feeding, water quality, or specific pathogen infections were identified. This study investigates intestinal flora alterations and host responses to uncover pathogenetic mechanisms and provide a foundation for devising effective disease surveillance and intervention strategies to mitigate the impact of enteritis on grouper aquaculture.
Enteritis-affected fish exhibited substantial differences in intestinal flora compared to controls (P = 0.001). Norank_f_Alcaligenaceae , detrimental to fish health, predominated in affected fish (91.76%), while Lactococcus , a probiotic genus, dominated in controls (93.90%). Genera with pathogenic potential like Achromobacter , Sphingomonas, and Streptococcus were more abundant in diseased fish, whereas probiotic genera like Enterococcus and Clostridium_sensu_stricto were enriched in controls. Transcriptomic analysis revealed strong inflammatory responses, impaired metabolic functions, tissue damage, and iron death signaling in the intestines and liver during enteritis. Correlation analysis showed potential pathogen groups positively associated with inflammation and tissue damage genes, and negatively with metabolic function genes.
In conclusion, intestinal dysbiosis, particularly the high abundance of Alcaligenaceae with pathogenic potential , likely triggered the enteritis outbreak. Alcaligenaceae and genera Achromobacter , Sphingomonas , and Streptococcus were identified as biomarkers for enteritis, while some species of Lactococcus , Clostridium_sensu_stricto , and Enterococcus showed promise as probiotics. These findings enhanced our understanding of enteritis pathogenesis, highlight intestinal microbiota shifts, and propose biomarkers for monitoring, probiotic selection, and enteritis management in fish.