Effects of fasting and feeding various diets on hepatic lipogenic enzyme activities in coho salmon (Oncorhynchus kisutch (Walbaum)).

The influence of fasting and diet composition on the time sequence of changes in hepatic lipogenic enzyme activities in coho salmon was investigated. Young coho salmon fed a high-carbohydrate diet for 3 weeks were then fasted for 2, 6, or 23 days. Liver preparations were assayed for fatty acid synthetase, citrate cleavage enzyme, malic enzyme, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities. Fasting the fish for 2 or 6 days did not influence the activities of these enzymes; however, by the end of the 23-day fast the activities of all these enzymes had decreased. Changing the diet of the fish from high-carbohydrate to high-fat had only a minimal influence on the activities of the hepatic lipogenic enzymes after 7 to 14 days. Longer-term studies demonstrated that high-fat diets did eventually depress lipogenic enzyme activities. The effect of fasting and feeding on the level of lipogenic enzyme activities was observed only after several weeks, in contrast to hours in the rat. This may reflect a difference between poikilothermous and homoiothermous animals.