Role of adiposity in food intake control of juvenile chinook salmon (Oncorhynchus tshawytscha)

Experiments were conducted re, determine if adiposity affected feed intake in juvenile chinook salmon (Oncorhynchus tshawytscha) with different nutritional histories. Fry were fed high-fat (23%) or low-fat (3%) diets at high (satiation) and low (one-half satiation) ration levels for 7 months before the start of the intake experiment. This pre-treatment produced fish averaging 22 g with 11.3% (high-fat diet) and 5.4%, (low-fat diet) body fat when fed to satiation or 11 g with 7.0% (high-fat diet) and 3.3% (low-fat diet) body fat when fed at one-half satiation. Experiment 1 had a 2 x 2 factorial design where duplicate groups of 20 fish from the high-ration groups (22 g) were fed high- (16%) or low- (4%) fat diets twice daily to satiation 6 days/wk for 3 weeks. Daily feed intake was recorded. The same protocol was used in experiment 2 on fish (40 fish per tank) from the smaller low-ration groups (11 g). Feed intakes on day 1, cumulative feed intakes after 21 days and plasma levels of insulin and insulin-like growth factor 1 (IGF-1) were compared using two-way ANOVA with initial whole body fat and dietary fat as the independent variables. In both experiments, high body fat led to significantly lower feed intake on day 1 and after 21 days of feeding. High dietary fat levels caused greater intake on day 1, but by the end of the experiments, this effect was not significant, suggesting some adaptation to the diets. Insulin in plasma showed greater response to dietary fat (high-fat diets causing higher insulin levels), whereas IGF-1 responded more to body fat level (high body fat led to higher IGF-1 levels). Our results show that in both fast-and slow-growing juvenile chinook salmon, adiposity plays a role in regulation of feed intake and that adiposity appears to interact with IGF-1. Dietary fat levels had transient effects on intake, but plasma insulin levels consistently reflected the dietary fat levels. An important implication of our findings is that food intake, and possibly growth, could be retarded if a feeding regime results in high body fat levels. (C) 1997 Elsevier Science Inc.