The Influence of Feeding Level on the Metabolic Rate of Largemouth Bass:

Evidence of a Compensatory Response

Steven H. Ranney

Despite their popularity, efforts to evaluate the accuracy of bioenergetics models (BEMs) predictions are often met with mixed success. Indeed, accuracy of BEM estimates has been shown to vary with feeding rate of fishes and may be associated with error in measuring fish metabolism.  Metabolic rate of fishes is a key parameter in energy budget formulations and can have a strong influence on accuracy of model output.   In addition to body mass and water temperature, factors such as salinity, density, heavy metals, and dissolved oxygen concentrations have been shown to affect metabolism in fishes but are generally not incorporated in parameter estimates.  In this study, I tested the hypothesis that metabolic rate of age-1 largemouth bass varies with feeding history.  Different feeding regimes were applied to two size classes of fish—i.e., maintenance rations for larger fish and ad libitum rations for smaller fish—over a nine week period such that body mass was similar prior to metabolic measurements.  After accounting for specific dynamic action, oxygen consumption was found to be significantly different between the two groups of fish.  Fish that were fed maintenance rations consumed only 63% of the oxygen that ad libitum fish consumed (0.00230 vs. 0.00368 g O₂/g/d), independent of body size or water temperature.  A paired t-test indicated that there were no significant differences between modeled and observed consumption values for fish fed ad libitum rations and the percent difference was moderate (11.5%), indicating good model fit.  For fish fed maintenance rations, a paired t-test indicated that there were significant differences between predicted and observed consumption values and the error in the model was high (43%).  After reducing the respiration parameter in the model by experimentally determined values, the percent difference dropped to 15%, suggesting that the model respiration value for fish fed maintenance rations was inaccurate.  Incorporating feeding history into sub-models for metabolism in BEMs will improve their predicative accuracy and allow fisheries biologists to make better decisions regarding fish populations.