Acute injury of liver in hybrid groupers (Epinephelus lanceolatus ♂ × Epinephelus fuscoguttatus ♀) under high-dose Edwardsiella ictaluri infection.

Edwardsiella ictaluri is a major fish pathogen that poses a serious threat to hybrid grouper in intensive aquaculture. This study evaluated the impact of E. ictaluri on liver health by analyzing histopathological changes, enzyme activity, and gene expression in infected hybrid grouper. Compared with the control group, infected fish exhibited markedly increased cytoplasmic vacuolation, inflammatory cell infiltration, nuclear pyknosis, and hepatocyte apoptosis. Moreover, biochemical assays revealed significantly elevated activities of glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT), and catalase (CAT). Transcriptomic analysis showed altered expression of genes associated with steroid hormone biosynthesis, PPAR signaling pathway, and protein digestion and absorption. Quantitative real-time polymerase chain reaction (qRT-PCR) further demonstrated increased mRNA expression of Nuclear Factor Kappa-B p65 (NF-κB p65), Toll-like Receptor 3 (TLR-3), Occludin (OCLD), Zonula Occludens-3 (ZO-3), and Fas cell surface death receptor (Fas). Redundancy analysis (RDA) revealed correlations of differentially expressed genes (DEGs) with cytoplasmic vacuolation and enzyme activities. Collectively, these findings reveal that E. ictaluri infection profoundly impairs liver health in hybrid grouper by disrupting hepatic structure, altering enzyme activity, and dysregulating pathways associated with immunity and metabolism.