INDUCTION OF DELTA-9-FATTY ACYL DESATURATION IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) LIVER BY DIETARY MANIPULATION

Hepatic stearoyl Delta 9-fatty acyl desaturation was demonstrated to b e modulated in trout by dietary manipulation. Desaturation was very lo w in hepatocytes isolated from the livers of starved fish with only 2% of [1-C-14]18:0 converted to Delta 9-desaturase products (18:1n-9 and 20:1n-9). After 6 weeks of feeding a commercial (fish oil-containing) pelleted trout diet, 50% of the radioactivity from [1-C-14]18:0 was c onverted to Delta 9-desaturase products. Another period of starvation, after the 6-week feeding period, reduced Delta 9-desaturation with on ly 4-5% of radioactivity from [1-C-14]18:0 being converted to Delta 9- desaturase products in hepatocytes. Subsequent refeeding produced a mu ch more rapid induction of Delta 9-desaturation with the activity sign ificantly increased after only 3 days refeeding and the activity resto red to the level before starvation after only 1 week of refeeding. The fatty acid composition of the diet appeared to be less important to t he induction of hepatic Delta 9-desaturation than the overall nutritio nal status because Delta 9-desaturation in livers of fish fed a high s aturated fatty acid diet, comprising 96% palmitic acid (16:0), was sim ilar to that of fish fed a fish oil-containing diet.