Abstract
A 2 × 3 factorial study was conducted to evaluate the effects of dietary lipid level on mitochondrial gene expression in mixed sex rainbow trout Oncorhynchus mykiss . Practical diets with a fixed crude protein content of 42%, formulated to contain 10% (42/10), 20% (42/20) and 30% (42/30) dietary lipid, were fed to triplicate groups of either low‐feed efficient ( F129 ; mean ± s.d. = 105·67 ± 3·04 g initial average mass) or high‐feed efficient ( F134 ; mean ± s.d. = 97·86 ± 4·02 g) families of fish, to apparent satiety, twice per day, for 108 days. At the end of the experiment, diets 42/20 and 42/30 led to similar fish condition factors, which were higher than that observed with diet 42/10 ( P F134 fish fed diet 42/10 showed the highest hepato‐somatic index, while there was no significant difference among all the other treatments ( P F134 fish fed diet 42/10 was used as the calibrator for gene expression analysis, the five genes selected for their involvement in lipid metabolism (complex I‐ nd1 , complex III ‐ cytb , complex IV ‐ cox1 , complex IV ‐ cox2 and complex V‐ atp6 ) were up‐regulated in the muscle and down‐regulated in both the liver and the intestine. There was a significant family × diet interaction regarding nd1 , cox2 and atp6 in the liver; nd1 , cytb , cox1 , cox2 and atp6 in the intestine, and nd1 , cytb , cox1 , cox2 and atp6 in the muscle ( P