Differences in fatty acid composition of gill and liver phospholipids between Steelhead trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar) under declining temperatures

This study investigated the fatty acid (FA) composition of gill and liver phospholipids in Steelhead trout (Oncorhynchus mykiss) (average weight: 75.45 +/- 6.27 g) and Atlantic salmon (Salmo salar) (average weight: 72.89 +/- 3.12 g) as water temperature decreased from 16 degrees C to 12 degrees C, 8 degrees C, 6 degrees C, 4 degrees C, 2 degrees C, and 1 degrees C. At normal temperature (16 degrees C), both gill and liver phospholipids of Atlantic salmon had lower saturated fatty acid (SFA) and higher unsaturated (UFA) compositions than those of Steelhead trout. Atlantic salmon was more sensitive to the temperature decline than Steelhead trout at the early stage of the experiment. Polyunsaturated fatty acid (PUFA) and monounsaturated fatty acid (MUFA) contents of Atlantic salmon liver phospholipids significantly increased as temperature decreased from 16 degrees C to 12 degrees C. However, both PUFA and MUFA contents decreased significantly at temperatures below 4 degrees C. In contrast, there was only a negligible decrease in MUFA content in Steelhead trout liver phospholipids at 1 degrees C. Starvation and cold stress influenced liver phospholipid FA composition in Atlantic salmon but not in Steelhead trout, suggesting that the latter can better adapt to low temperatures. Changes in gill phospholipid composition in response to temperature fluctuations were species-specific. When the ambient temperature was below 8 degrees C, SFA content of gill phospholipids decreased whereas PUFA content increased and MUFA content was unaltered in Atlantic salmon. Although the FA composition of gill phospholipids in Atlantic salmon was altered at 6 degrees C, it remained stable as temperature further decreased. These results indicate that the FA composition of gill phospholipids in Atlantic salmon is less influenced by starvation stress than that of liver phospholipids. Moreover, fewer changes in FA composition were observed for gill as compared to liver phospholipids in both species of fish. Our results can be useful for optimizing Atlantic salmon and Steelhead trout aquaculture systems.