Proline enhances immune defense and mitigates hypersalinity stress in the razor clam Sinonovacula constricta

Proline, an osmotic regulatory protectant characterized by low molecular weight and high water solubility, has been proven to rapidly accumulate in aquatic organisms under hypersalinity stress. Nevertheless, the specific mechanisms by which proline enhances hypersalinity tolerance in bivalves remain unclear. In this study, exogenous proline was supplemented to maintain a concentration of 5 μg/mL in hypersaline aquaculture water (32 ppt), aiming to investigate its alleviating effects on gill damage and oxidative stress in razor clams (Sinonovacula constricta). The results indicated that after 96 h of acute salinity stress, the survival rate of razor clams decreased to 84 %, while proline supplementation increased survival rate to 95 %. Proline prevented gill filament damage, enhancing their length by 1.5-fold compared to controls (P <0.01). The razor clams supplemented with proline exhibited enhanced total antioxidant capacity, increased antioxidant enzyme activities, and reduced levels of oxidative stress markers such as reactive oxygen species (ROS) and malondialdehyde (MDA). These findings indicate that proline supports gill integrity, enhances antioxidant capacity, thereby boosting immune function, and improves the razor clam's tolerance to high salinity.