Effects of water temperature and air exposure on the lysosomal membrane stability of hemocytes in pacific oysters, Crassostrea gigas (Thunberg)

Neutral red retention (NRR) assay was used to evaluate lysosomal membrane integrity in hemolymph from Pacific oysters subjected to rapid and gradual water temperature changes and exposure to different air temperatures. Recovery of the lysosomal membrane after air exposure was also evaluated.The NRR times of oysters held in 5, 15 and 25 °C seawater for 7 days were 60.0 ± 0.0, 145 ± 5.0, and 66.3 ± 8.5 min, respectively. The rapid water temperature change experiment showed that the recovery of lysosomal membrane integrity took longer than destabilization in Pacific oysters. The gradual temperature change experiment indicated that 13 to 17 °C was the optimal water temperature range for maintaining lysosomal membrane integrity. Further assays showed that the NRR time at 5, 15 and 25 °C was not influenced by the speed at which the temperature was changed.The results from the air exposure experiment suggest that within the first 1.5 h the integrity of the lysosomal membrane was mainly affected by air temperature. From 3 h onward both exposure duration and air temperature affected the integrity of lysosomal membrane. Higher air temperatures resulted in shorter NRR times than lower temperatures did at every time point after 12 h. During recovery in 15 °C water after 72 h air exposure, significantly shorter time periods were required for NRR times to reach control levels in oysters exposed to 5 °C than those exposed to 15 and 25 °C, indicating that exposure to lower air temperatures caused less damage to lysosomal membranes in Pacific oysters.