Oligochitosan modulates non-specific immunity against Edwardsiella ictaluri infection in hybrid groupers Epinephelus fuscoguttatus f × E. lanceolatus m

Edwardsiella ictaluri is a pathogenic bacterium that poses a significant threat to the economic viability of aquaculture. However, the effects of E. ictaluri infection on the non-specific immune response of hybrid grouper and the regulatory mechanisms of oligochitosan in modulating the infection are poorly understood. We investigated the impact of oligochitosan supplementation on the growth performance, biochemical parameters, immune response, and apoptosis in hybrid grouper infected with E. ictaluri. The results showed that oligochitosan significantly improved the weight and length of hybrid grouper, whereas E. ictaluri infection reduced their growth performance. Histopathological analysis of the head kidney showed no significant differences among the groups. Biochemical analysis revealed that E. ictaluri significantly increased the activity of serum glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT), while decreasing the activities of catalase (CAT) and superoxide dismutase (SOD), with oligochitosan ameliorating these effects. E. ictaluri infection also significantly elevated the GOT activity in the head kidney while reducing CAT and SOD activities. The analysis of inflammatory factor expression revealed that E. ictaluri significantly increased the levels of IL-8, TNF-α, and IKKα, whereas oligochitosan effectively decreased these inflammatory markers. Apoptosis gene expression analysis indicated that E. ictaluri infection significantly upregulated bax, caspase-3, and caspase-8, while supplementation with oligochitosan reduced their expression levels. TdT-mediated dUTP nick-end labeling signals were significantly increased following E. ictaluri infection, while supplementation with oligochitosan notably reduced them. In conclusion, oligochitosan can regulate growth, immune response, and apoptosis, potentially protecting hybrid grouper infected with E. ictaluri.