THERMAL ADAPTATION AFFECTS THE FATTY-ACID COMPOSITION OF PLASMA PHOSPHOLIPIDS IN TROUT

The adaptive changes in the fatty acid (FA) composition of plasma phos pholipids (PL) in response to alterations in environmental water tempe rature were investigated in juvenile rainbow trout (Oncorhynchus mykis s). The changes observed during thermal adaptation from 22 degrees C i n summer to 8 degrees C in winter were reproduced by laboratory cold a cclimation (CA) at 6 degrees C of 22 degrees C-summer-acclimated anima ls. In cold-acclimated and winter-acclimated trout, the increase in th e unsaturation of PL fatty acids was mainly due to an enrichment of ap proximately 7% in the total weight percentage of 22:6n-3, while a conc omitant significant decrease in the levels of 18:0 and of the monoenoi c n-9 FA was observed. A time course study revealed that the changes i n PL fatty acids became significant after 10 d of CA and were complete after one month. These changes in the composition of the fatty acyl c hains of plasma total PL indicate that the FA composition of plasma li poprotein PL does not remain constant during thermal adaptation. This would suggest that plasma lipoproteins provide a rapid systemic supply of lipids containing more or less unsaturated FA during thermal adapt ation of poikilothermic animals.