Seasonal variations in the lipid composition of the steelhead trout, Salmo gairdneri Richardson, associated with the parr‐smolt transformation

Total lipid and lipid class composition of selected tissues and serum were determined for juvenile steelhead trout Salmo gairdneri, during the smolting period between 25 January and 19 April 1982. The total lipid content of the serum, liver, light muscle and dark muscle was significantly depleted during smolt transformation. Mesenteric fat total lipid concentration fluctuated little over the sampling period. Phospholipids of muscle and mesenteric fat exhibited little seasonality. Cholesterol was significantly depleted from dark muscle and liver. Large stores of triacylglycerol (TGL) in the parrs' mesenteric fat, dark muscle and liver implicate these tissues as lipid depot organs. In those tissues depleted of lipid, TGL concentrations were reduced more than any other lipid class. This supports the hypothesis that increased catabolism is the cause of loss of body fat during salmonid smolt transformation.