Lipid dynamics in anadromous Arctic charr, Salvelinus alpinus (L.): seasonal variations in lipid storage depots and lipid class composition

Changes in lipid class composition of tissues of anadromous Arctic charr, Salvelinus alpinus, were studied in relation to seasonal patterns of lipid deposition and lipid mobilisation. Charr of a north Norwegian population were collected in late May when fish were migrating towards the sea, and in mid-July when the fish re-entered fresh water. Some maturing fish captured in mid-July were held in captivity until late September to assess lipid dynamics associated with maturation. The carcass (head, fins, skeleton and skin) accounted for approx. 50% of the total body lipid content when the fish re-entered fresh water from the sea. Triacylglycerols (TAG) comprised 75-80% of the carcass lipid in ascending charr, confirming that the carcass is a major lipid depot. The skeletal muscle also represented a major lipid store: muscle of ascending charr contained 35-40% of the body lipids, with TAG being dominant (approx. 75% of muscle lipid). The gut (gastrointestinal tract and visceral lipid) and liver of ascending charr each held only 4-5%; of the body lipid, TAG being the dominant lipid class in both of these depots (Gut TAG: 60-65%; Liver TAG: 50-55%). Body lipid decreased 30-40% during maturation: lipids were depleted from all depots, but mobilisation of from the carcass and muscle was quantitatively the most important. In mature females, the ovaries held almost 25% of the body lipid, with the proportion of TAG exceeding that of polar lipids (PL)(TAG: 62%; PL 12.4%). In the mature males, the testes accounted for less than 3% of the total lipids. TAG tended to dominate the testis lipids (TAG: 29.5%), but there were also quite high proportions of free fatty acids, cholesterol and polar lipids (FFA: 23.5%; C: 15%; PL 9.7%). Females lost approx. 80% of their body lipid during spawning and overwintering, the majority of this being TAG. Males also lost large amounts of TAG during the winter, but in contrast to the females lipid depletion amounted to only 50-55% of that present at the time of ascent into fresh water.