New information concerning respiratory metabolic rates of juvenile mosquitofish (x = 915 mg O2 kg-1 h-1 at 20 C) was applied to existing data on mosquitofish respiration and combined with findings on growth and food consumption rates to determine percentages of net ingested energy used for growth and respiration over a 10 ? 35 C temperature range. The energy percentage used by mosquitofish for respiration was minimized at 25 ? 30 C while that used 'for growth (= food conversion efficiency) was maximized at the same temperature. A calculated growth potential index, derived from an overall energy balance equation, was also maximized at the 25 to 30 C range and proved to be closely correlated with food conversion efficiency (r = 0.98). Possible future applications of the growth potential index for estimating food conversion efficiencies in field populations of fishes are suggested.
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