Responses to thermal and salinity stress in wild and farmed Pacific oysters Crassostrea gigas.

The Pacific oyster Crassostrea gigas was introduced from Japan to many countries in the world for oyster farming, resulting in the establishment of wild populations in intertidal zones and resource competition with local faunas. This study examined physiological responses of wild oysters and farmed oysters to thermal (15°C, 25°C, 37°C and 44°C) and salinity stress (39, 50 and 60ppt). The wild oysters produced more 72kDa heat shock proteins when the temperature increased from 15°C to 25°C and 37°C and the salinity increased from 39 to 50 and 60ppt. However, the amount of 69kDa heat shock protein was similar between farmed and wild oysters when the temperature increased from 15°C to the sublethal temperature 37°C, but it was lower in wild oysters than in farmed oysters when the temperature increased from 15°C to the lethal temperature 44°C. In the tissues, wild oysters used more glycogen to promote metabolic activities by increasing the level of AEC (adenylate energy charge). The results suggest that farmed oysters might have limited ability to cope with heat stress due to low energy reserve and glycolysis activity for HSP synthesis. This study provides experimental evidence on differential responses between wild and farmed oysters to temperature and salinity changes, leading to a better understanding on the pattern of distribution for invading oyster species in the marine environment and the adaptation of marine invertebrates to the threat of climate change.