Background Coelomactra antiquata is an economically important marine shellfish species that is valued for both its culinary and medicinal properties. In recent years, the artificial breeding of C. antiquata along the coast of Zhanjiang has been successful, and large-scale proliferation and release have been carried out in the coastal areas. The large amount of precipitation in summer in the coastal area of Zhanjiang has caused a significant decrease in the salinity of the coastal waters, which poses a great threat to C. antiquata.

Objective The changes of low salinity tolerance and related enzyme activities of C. antiquata were investigated.

Methods C. antiquata, collected from the Xuwen sea area of Zhanjiang, was used as experimental materials. The gradual and acute dropping salinity groups were set up to explore the low salinity tolerance of C. antiquata through comparing the 50%CSMin (the salinity at which half of the C. antiquata survived) during the gradual dropping salinity process and the 72 h LS₅₀ (the salinity at which the survival rate was 50% within 72 hours) during the acute dropping salinity process. The gill tissues of acute dropping salinity groups at 0 h, 6 h, 12 h, 24 h and 48 h were taken to investigate the immune indicators under low salinity stress, including Na⁺/ K⁺-ATPase (NKA), superoxide dismutase (SOD), catalase (CAT), alkaline phosphatase (AKP), acid phosphatase (ACP) and lysozyme (LZM).

Results The minimum survival salinity (SSMin) was 18.22, the minimum critical salinity (CSMin) was 10.18, and the salinity at which the survival rate was 50% (50%CSMin) was 13.07. The median lethal salinity after 72 h (72 h LS₅₀) was 16.86. The NKA, CAT, SOD, AKP, ACP and LZM of gill tissue were significantly affected by acute dropping salinity stress for 48 h (P<0.05). CAT, SOD, ACP, AKP and LZM all showed a trend of increasing first and then decreasing, and their minimum values were 75.36 U/mL, 293.8 U/mL, 0.292 U/L, 0.321 U/L and 5.283 U/mL, respectively. NKA showed an upward trend, and the minimum value within 48 h was 0.339 U/mL.

Conclusion At the same salinity, the survival rate of the acute dropping salinity groups were significantly lower than that of the gradual dropping salinity groups. This study provides an important theoretical basis for the further study of the low salinity antioxidant response mechanism in C. antiquata, and also offeres an important guiding for the artificial breeding of C. antiquata.