Laboratory evaluation of two bioenergetics models for brown trout

Laboratory growth and food consumption data for two size-classes of brown trout Salmo trutta subjected to three distinct feeding regimes at two temperatures were used to evaluate the ability of two bioenergetics models to predict fish growth. Accuracy of cumulative consumption predictions was also tested for one of the models. Consumption-dependent prediction error has been commonly observed in bioenergetics models for other fish species; model errors for predicting relative growth rate of individual fish were regressed on observed mean daily consumption rate to assess whether the two bioenergetics models exhibited this type of error. Both models yielded unbiased estimates of brown trout growth that were within 1-12% of observed values across the range of fish sizes, water temperatures, and ration levels tested. For regressions of predicted versus observed final weight, the Bonferroni joint 95% confidence intervals for slope included 1 and confidence intervals for the y-intercept included 0 for both models. No significant intermodel differences in percent error for predicting final weight of fish in feeding trials were observed. Predicted cumulative consumption values were within 8-15% of corresponding observed values. Neither model exhibited significant consumption-dependent error for predicting brown trout growth, in contrast to results of several previous laboratory evaluations of bioenergetics models for other fish species. Absence of consumptiondependent error in the two brown trout models may be a result of (1) incorporating feeding rate dependence of egestion and excretion into these models and (2) using egestion and excretion parameters that were not borrowed from other species. Results of this evaluation corroborate the utility of these bioenergetics models for predicting growth and consumption for brown trout under the range of fish sizes, water temperatures, and ration levels tested.