Cryptocaryon irritans, a ciliated protozoan parasite, is the causative agent of marine white spot disease and results in significant economic losses in mariculture. In this study, golden pompano (Trachinotus ovatus) were challenged with C. irritans at different infection doses (2000, 4000, and 8000 theronts per fish) for 48 h to evaluate histopathological, oxidative stress, immune, and intestinal microbiota responses. Histopathological analysis revealed pronounced tissue damage in the gills, skin, intestine, and liver, with severity positively correlated with infection intensity. Typical lesions included intestinal mucosal damage, hepatic vacuolation, gill epithelial hyperplasia, and skin epidermal thickening. Hepatic malondialdehyde (MDA) levels increased significantly with infection intensity, while superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) showed non-linear activation patterns. Catalase (CAT), alkaline phosphatase (AKP), and acid phosphatase (ACP) activities were consistently suppressed. Immune-related gene expression exhibited tissue-specific regulation, with myd88 downregulated in gills but upregulated in skin, while pro-inflammatory cytokines (il-1β and il-8) and il-10 were significantly elevated. Infection also altered intestinal microbiota composition, reducing beneficial bacteria (e.g., Photobacterium) and increasing opportunistic pathogens such as Vibrio. These findings provide insights into host–parasite–microbiota interactions in T. ovatus and improve our understanding of the physiological and immune responses of fish to C. irritans infection.
Hu et al. (Tue,) studied this question.