Microalgae Parasite Diseases of Mytilus galloprovincialis: Infections, Immunology and Antioxidant Defense

<i>Coccomyxa parasitica</i>-like algae pose a growing threat to bivalve aquaculture. In this work, for the first time under controlled conditions, the effect of the green parasitic microalgae of genus <i>Coccomyxa</i> sp. in the Sea of Japan on the immune and antioxidant protection of <i>Mytilus galloprovincialis</i> was studied in two ways of infection-through filtration (with feed) and injection (into an adductor). By day 7, mortality in both experimental groups reached 68%. The phagocytic activity of hemocytes significantly decreased in the feed group, which may be due to the masking of the parasite as a food particle. Despite transcriptional activation of catalase and superoxide dismutase genes in hemocytes upon injection, a decrease in enzyme activity and an increase in lipid peroxidation were observed in the gills, indicating local oxidative stress. Catalase activity in the gills was increased when mussels receive cells as food. DNA damage in hemocytes did not reach statistical significance. After injection, there was a significant decrease in the galectin gene expression. The data obtained confirm that <i>Coccomyxa</i> sp. is an active parasite capable of infecting the Mediterranean mussel and modulating the host's defense systems.