Combined effects of diets and temperature on mitochondrial function, growth and nutrient efficiency in rainbow trout (Oncorhynchus mykiss).

A 4×3 factorial experiment was conducted to evaluate the effects of two dietary protein sources (mixed fishmeal/plant protein-, and plant protein- based diet), two dietary lipid levels (10% and 20%) and three water temperatures (10°C, 14°C, and 18°C) on the growth performance, nutrient utilization efficiencies and mitochondrial enzyme complex activities in rainbow trout Oncorhynchus mykiss (average weight±SD, 39.5±5g) over a 180day rearing period. At the end of the experiment, weight gain (WG), condition factor (CF), and feed efficiency (FE) were significantly affected by diet×temperature interaction (P<0.05). Specific growth rate (SGR) was significantly affected by increasing temperature (P<0.05). The plant protein-based diets led to a higher CF than the mixed fishmeal/plant protein-based diets. The protein productive value (PPV), protein efficiency ratio (PER), lipid efficiency ratio, (LER) and lipid productive value (LPV) were all significantly affected by diet×temperature interaction (P<0.05). The diet×temperature interaction also had significant effects on mitochondrial enzyme complexes II, V and citrate synthase in the liver, complexes II and IV in the intestine, and complex IV in the muscle (P<0.05). Temperature had a significant main effect on the activity of the enzymatic complexes I and III in the liver, complex III and citrate synthase in the intestine, and complexes I, II, III, V and citrate synthase in the muscle (P<0.05). Diet had a significant main effect on complexes I and III in the liver, complexes II and III for the intestine and complexes I and II in the muscle (P<0.05). The significant temperature x diet interaction observed has practical ecological implications explicitly demonstrating how changes in temperature regimens as anticipated in the rising global temperature can influence organismal performance in relation to changes in dietary formulations (replacing fishmeal based diet with plant protein based ingredients). To illustrate the practical application of the observations from this study, the most economical and cost effective way to produce rainbow trout would be to use 40/10PP diet at 14°C because fish fed this treatment had a weight gain comparable to that of the fish fed the more expensive experimental diets (40/10 FM/PP, 40/20 FM/PP, and 40/20 PP).