Relation between dietary lipid level and voluntary feed intake, growth, nutrient gain, lipid deposition and hepatic lipogenesis in rainbow trout

Four diets with differing lipid contents (15, 20, 25 or 30% DM) were tested on small (initial body weight: 27 g) and larger (IBW: 93 g) rainbow trout (Oncorhynchus mykiss) fed on demand or by hand, respectively. In both trials, voluntary feed intake was inversely related to dietary lipid levels. Protein efficiency increased when dietary fat content increased. Final whole-body lipid content was positively related to dietary lipid levels. The main sites of lipid storage were visceral adipose tissue and to a lesser extent muscle. Increased fat deposition in the visceral cavity of young trout was due to both hyperplasic and hypertrophic responses and in larger trout mostly due to a hypertrophic response. Liver activities of glucose-6-phosphate dehydrogenase and fatty acid synthetase were negatively correlated with fat intake and positively with starch intake, whereas malic enzyme was little affected by dietary treatments.