Effects of boring sponge Pione vastifica (Hancock, 1849) infestation on redox status and histological structure in Pacific oyster Magallana gigas (Thunberg, 1793) gills

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The Pacific oyster, Magallana gigas (Thunberg, 1793), is the most widely cultivated bivalve species in the world. Despite the oyster's resistance to most pathogens, oyster farms are increasingly suffering losses due to infestation by various boring agents, particularly boring sponges. Boring sponges Pione vastifica (Hancock, 1849) penetrate and destroy the shell of the oysters, creating a network of channels and chambers in the shell. This ultimately results in a reduction in the marketability and barrier protection of oysters, as well as an impairment of their functional status. The objective of this study was to identify the mechanisms of oyster response to exposure to the boring sponge and to assess the health status of the species in the context of its ecological and economic importance. This paper examines the effect of the boring sponge on the organism of Pacific oysters M. gigas, namely on the level of lipid peroxidation and the activity of the main antioxidant enzymes (superoxide dismutase - SOD, catalase - CAT, glutathione peroxidase - GPx), as well as histopathological changes in the gills of oysters with different degrees of boring sponge infestation. In contrast to the SOD activity, the CAT and GPx activities were found to be dependent on the extent of damage inflicted upon the shell by the boring sponge. In the initial phase of shell damage (1 and 25%), the CAT activity exhibited no notable deviation from the control level. However, the GPx level demonstrated a pronounced decline. In the second stage (26-50% of damage), there was an increase in CAT activity, and the levels of GPx returned to control levels. Despite a low level of antioxidant defense activity, an increase in lipid peroxidation was observed. In the fourth stage (76-100% damage), the highest level of lipid peroxidation was observed. This was accompanied by an increase in CAT production and a decrease in GPx activity. However, no significant disturbances in the structure of gill tissues were found with an increasing degree of damage caused by the spread of boring sponges. In our study, only local histological abnormalities were observed in stages 2, 3, and 4 of infection. The results of the present work demonstrate the influence of the boring sponge infestation process on the redox balance of oyster gill.