The combined effects of feeding time and dietary fat levels on feed intake, growth and body composition in rainbow trout

Abstract

The combined effects of feeding time (morning and evening) and dietary fat concentration on feed intake, growth, body composition and lipid tissue distribution were examined in rainbow trout fed on demand. To that purpose, diets with low (LE, 6% lipid) or high energy concentrations (HE, 24% lipid) were used in four treatments that combined provision of the same (HE–HE or LE–LE) or different (HE–LE, LE–HE) diets at morning and evening meals. Digestible energy intakes of the LE–HE (229 kJ kg^–1 d^–1) and HE–HE (269 kJ kg^–1 d^–1) groups were significantly different. There was no significant difference in the amount of energy intake between the two meals of the day in any of the treatments. The main effect of dietary treatment was on lipid intake; fish in the HE–HE, HE–LE and LE–HE treatments ingested approximately 3, 2.2 and 1.8 times more lipid than those on the LE–LE treatment. Growth, weight gain and protein gain were not affected by dietary treatment, but lipid gain reflected lipid intake; fish in the HE–HE, HE–LE and LE–HE treatments gained approximately 2.6, 2.1 and 1.7 more lipid than did fish on the LE–LE treatment. Body composition was significantly affected by dietary treatment; whole body lipid content reflected lipid gain, and visceral lipid concentration was affected in a similar way to whole-body lipid. On the other hand, muscle lipid concentrations were similar in fish submitted to the HE–LE, LE–HE, and LE–LE treatments (< 4%), and were lower than in fish on the HE–HE treatment (ca. 5.5%). Consequently muscle lipid concentration was not directly related to lipid intake, because lipid intakes of fish on HE–LE and LE–HE treatments was higher than in those on the LE–LE treatment, while muscle lipid concentration was lower. Thus feeding fish with different diets in the morning and evening might have potential as a tool for manipulating lipid distributions and concentrations without major adverse effects on growth.