The Pacific oyster (Magallana gigas), which inhabits the dynamic tidal zones of coastal shelves, experiences frequent fluctuations in environmental parameters, including salinity. This study investigates the physiological and immunological responses of M. gigas to hypo- (8, 10, and 14 ppt) and hyperosmotic (24 and 30 ppt) stress. Specifically, we examined the effects on cellular immunity, along with the response of key antioxidant enzymes in gill tissue. Measured parameters included hemolymph cellular composition, hemocyte phagocytic activity, alterations in mitochondrial membrane potential, levels of spontaneous reactive oxygen species (ROS) generation, and the activity of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) in the gills. Additionally, oyster mortality rates and whole-organism oxygen consumption were monitored at key salinity points. The results indicate that hyposaline conditions triggered an increase in aerobic metabolic intensity, evidenced by elevated mitochondrial membrane potential in hemocytes at 8 ppt and increased respiratory activity at 14 ppt. Concurrently, there was a rise in granulocyte count and enhanced activity of SOD (8 ppt) and CAT (8, 10, and 14 ppt). Under hypersaline stress, elevated ROS levels (24 ppt) and increased CAT (24 and 30 ppt) and SOD (30 ppt) activities were observed. Hyperosmotic stress did not induce significant changes in overall oxygen consumption or the intensity of hemocyte aerobic metabolism. Phagocytic activity remained unchanged across all treatments. Notably, oyster survival was 100% under both hypo- and hypersaline conditions. These findings demonstrate the activation of a robust compensatory response and highlight a high adaptive potential in M. gigas to salinity stress. The observed intensification of aerobic metabolism at both organismal and cellular levels appears to effectively support cellular immune function during osmotic perturbation.
Andreyeva et al. (Fri,) studied this question.