The influence of temperature adaptation on the composition of the neutral lipid fraction of rainbow trout (Salmo gairdneri) liver

Abstract

AbstractRainbow trout (Salmo gairdneri) acclimated to 20°C possessed significantly greater quantities of total neutral lipid, triglyceride, and free fatty acids, and smaller quantities of hydrocarbons in their livers than 5°C‐acclimated animals. Regardless of acclimation temperature the relative abundance of the various neutral lipid classes was triglyceride > cholesterol ester > free cholesterol > diglyceride > free fatty acid > wax ester and hydrocarbon. Two patterns of compositional change were observed in response to alterations in environmental temperature. Depot lipids (triglyceride and wax ester) became more unsaturated at lower ambient temperatures due primarily to moderate increases in the content of monoenes, and larger increases in the content of both dienes and polyunsaturates. Increased unsaturation of the triglyceride fraction was mediated primarily by an accumulation of unsaturates belonging to the linoleic and linolenic acid families, whereas oleate‐ and linoleate‐derived fatty acids accumulated in the wax ester fraction. The remaining neutral lipid fractions (free fatty acids, diglycerides, and cholesterol esters) all experienced a decline in the content of unsaturated fatty acids at reduced temperatures due primarily to a loss of monoenes from each fraction and a loss of dienes from the diglyceride and cholesterol ester fractions; unsaturated fatty acids belonging to the oleate family were preferentially lost from these neutral lipids upon cold acclimation. These results suggest that in response to a reduction in environmental temperature, a reorganization of lipid metabolism occurs which in volves a selective uptake of predominantly linolenate‐derived unsaturated fatty acids into phospholipids and linoleate‐derived unsaturated fatty acids into depot lipids, resulting in a free fatty acid fraction enriched in saturated fatty acids.