Bacterial challenge undermines the innate immune response in Hyriopsis cumingii

The ecologically and economically important bivalve species Hyriopsis cumingii is affected by numerous bacterial diseases, but the effects of these harmful bacteria on the antioxidant responses and histological alterations of H. cumingii are unclear. This study evaluated the effects of common pathogenic infections on immune function in H. cumingii. A series of antioxidant enzyme activities, total haemocyte counts, and histopathological changes were measured at 24, 48, and 96 h post infection (hpi) with three pathogens (Aeromonas hydrophila, Streptococcus agalactiae, and Pseudomonas fluorescens). All enzyme activities sharply decreased or remained constant at 24 hpi, except for acid phosphatase and alkaline phosphatase activities in the P. fluorescens-infected group. However, peroxidase activity significantly increased at 24 and 48 hpi in all treatments (p