From November to May, the lipid mass in the viscera and carcass of juvenile Atlantic salmon Salmo salar that were undergoing smolt transformation prior to seaward migration (‘early migrants’) were significantly greater than those of their siblings that would
delay migration for at least a further year. During winter (November‐February), the depletion of lipid associated with the viscera was significantly greater in early migrants, whilst lipid depletion in the remaining carcass was greater in delayed migrants. Early migrants continued to
deplete both lipid compartments in spring (February‐May), whereas delayed migrants depleted visceral lipid but replenished carcass lipid over the same period. Fatty acid accumulation rates (a measure of storage lipid synthesis rates) were two to six times greater in visceral than in
carcass lipid throughout the study, suggesting that lipid turnover is much more rapid in the viscera. There were no differences in fatty acid accumulation rates between migrant groups in November, despite the much lower food consumption rate of delayed migrants at that time, suggesting that
these fish allocated a larger proportion of their nutritional resources to lipid synthesis. In the carcass lipid of early migrants, and in both the visceral and carcass lipid of delayed migrants, the fatty acid accumulation rate was negatively correlated with lipid mass. Fatty acid accumulation
rates increased from November to February in both visceral and carcass lipid in the two migrant groups. The fatty acid accumulation rate in carcass lipid was significantly higher in delayed migrants than in early migrants in February, but not in May. These results support the hypothesis that
life history strategies involving rapid growth will result in a relatively low allocation of resources to lipid reserves.
Fish Biology Group, Division of Environmental and Evolutionary Biology, Institute of Biomedical and Life Sciences, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQ, U.K. 2:
University Field Station, University of Glasgow, Rowardennan, Glasgow G63 0 AW, U.K.