Effect of microplastic binding capacity on antioxidant and immune responses of Korean rockfish Sebastes schlegeli in a co-exposure environment with microplastics and Streptococcusiniae.

Korean rockfish (Sebastes schlegeli) aquaculture, which predominantly occurs in coastal regions, encounters challenges such as reduced productivity owing to microplastics and bacterial contamination. Microplastic adsorb bacteria and accumulates in fish, inducing alterations in antioxidant and immune responses. Numerous studies have examined the interaction between microplastics and external pollutants such as heavy metals and physiological changes in fish; however, studies on the effects of combined exposure to microplastics and bacteria on physiological changes in fish remain limited. Therefore, we investigated the effects of combined exposure to microbead (MB) and Streptococcus iniae (S. iniae) on the antioxidant and immune responses of Korean rockfish. Korean rockfish were exposed to single and combined environments of 0.2 μm MB at 5 and 50 beads/L and S. iniae at 1 × 105 and 1 × 107 CFU/mL for 5 days. MB accumulation in gill and intestine tissues was examined, and copy number changes of S. iniae in liver and spleen tissues were analyzed. The mRNA expression levels of antioxidant enzymes (SOD and CAT) and immune-related genes (IL-1β, IL-6, CCL25, and TNF-α) were analyzed in the liver tissue, while changes in plasma MDA and lysozyme levels were evaluated as an additional immune-related factor. Combined exposure to high concentrations of MB and S. iniae increased the accumulation of MB and the copy number of S. iniae than that of a single exposure. This also increased the mRNA expression of antioxidant enzymes and immune response genes. These results indicate that the accumulation of MB in Korean rockfish, depending on its concentration, can bind with S. iniae, inducing changes in the copy number of S. iniae and affecting antioxidant and immune responses. This study is expected to provide fundamental academic data for understanding the physiological and immunological responses of marine organisms exposed to the combined effects of MB and S. iniae.