EFFECTS OF TEMPERATURE-VARIATIONS ON DIETARY-LIPID ABSORPTION AND PLASMA-LIPOPROTEIN CONCENTRATIONS IN TROUT (ONCORHYNCHUS-MYKISS)

In juvenile rainbow trout (Oncorhynchus mykiss) the peak of dietary li pid absorption occurred later at low compared with high temperature. R apid temperature variations modified plasma concentrations of glucose, lipids and lipoproteins, with no effect on free glycerol. The concent ration of these parameters was not affected during the progressive sea sonal temperature changes. The plasma concentration of very low densit y lipoproteins (VLDL) increased by two- to three-fold within two days after the onset of cold acclimation (CA) or warm acclimation, independ ently of alterations in dietary lipid absorption. The high concentrati on of VLDL induced an increase in low density lipoproteins (LDL) conce ntration after several days. CA induced a rapid and transitory decreas e in the concentration of high density lipoproteins (HDL) of about 20% . Incomplete successive acclimations resulted in a cumulative effect o n the increase of VLDL (10-fold) and of LDL (three-fold). In cold-accl imated trout, the persistent hypertriglyceridemia and high plasma conc entration of VLDL observed for several weeks after fasting suggest a l ong-term increase in the secretion of hepatic VLDL. The results indica ted that plasma lipoprotein concentrations appear to be sensitive to t he thermal adaptation process in trout exposed to rapid temperature va riations.