Association of mitochondrial function with feed efficiency in rainbow trout: Diets and family effects

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A 2 × 4 factorial experiment was conducted to evaluate the effects of commercial diets (40/10 or 45/19% protein/fat, Melick Aquafeed, Inc.) and rainbow trout families (designated as 076, 254, 256 or 257) on the performance, mitochondrial gene expression, and mitochondrial respiratory chain enzyme activities in the liver, muscle and intestine. Four families of rainbow trout (average weight = 100, 97, 82 and 72 g for 076, 254, 256 and 257, respectively) were stocked into twenty four 152-L aquaria at a density of 10 fish/aquarium. Three aquaria were used for each treatment. Fish were fed twice daily to apparent satiation for 16 weeks. Results indicated that family type had significant (P < 0.05) main effects on weight gain, feed consumption, feed efficiency and specific growth rate. Diet composition had no significant (P > 0.05) main effect on weight gain, absolute feed consumption, feed efficiency, specific growth rate, and condition factor, regardless of the family type. There was no significant (P > 0.05) interaction between family and diet composition for weight gain, feed consumption, feed efficiency, specific growth rate, and condition factor. Family with the least weight gain and feed effciency had significantly (P < 0.05) low nutrient utilization efficiencies in terms of protein efficiency ratio, protein productive value, energy efficiency ratio, energy productive value, and lipid productive value. There were variations in the expression levels of some mitochondrial encoded genes and mitochondrial complex enzyme activities in different tissues. Family and diet caused significant down-regulation of complex I gene (ND1) in the liver and its up-regulation in the intestine and muscle tissues. Generally, family with high feed efficiency and better nutrient utilization had higher numerical values for respiratory chain enzyme activities, down-regulation of hepatic complex I ND1 gene and its up-regulation in the intestine and muscle compared to the low feed efficiency family. The mitochondrial respiratory chain complex activity was significantly affected by family and diets in the liver, and muscle for complex I; liver and intestine for complex II; liver, intestine and muscle for complex III; liver and muscle for complex IV. Regardless of family, fish fed diet containing 45% protein and 19% fat had significantly higher (P < 0.0001 to P = 0.0426) levels of activities in the liver and muscle for complex I, intestine for complex II, muscle for complex III, and liver for complex IV. These data demonstrate that family 257of rainbow trout appears to possess superior traits in growth performance compared with the family 256. Our data indicate that genetic factor has important impact on rainbow trout production and that a commercial diet containing 40% dietary protein and 10% dietary fat is as good as diet with higher protein and fat levels for enhanced growth performance, gene expression, and mitochondrial enzyme activities.