Cooperative Fish and Wildlife Research Units Program: South Dakota
Education, Research and Technical Assistance for Managing Our Natural Resources

Metabolic rate is a key parameter in fish energy budgets that strongly influences the output of bioenergetics models. In this study, we tested the hypothesis that metabolic rate varies with growth history of age-1 largemouth bass. Two groups of fish were fed alternating maintenance or ad libitum rations of fathead minnow, so that over a 9-week period, initial and ending size of fish was similar. After 9 weeks, oxygen consumption was measured using static, closed respirometry. Although final body weight was similar between the two groups (means, 104 to 108 g), specific oxygen consumption for fish fed maintenance rations (0.094 mg O₂ g^-2 h^-1) was 38% less than that measured for fish fed ad libitum (0.152 mg O₂ g^-2 h^-1). Bioenergetic estimates of food consumption were similar to observed values for fish fed ad libitum (~7% error), but for fish fed maintenance rations, the model overestimated food consumption by 65%. By accounting for changes in metabolic rate owing to reduced feeding, error in model estimates of food consumption was reduced. These findings shed new insight on factors associated with consumption-dependent error in bioenergetic models and highlight the importance of feeding history on metabolic rate of fish. Incorporating growth-dependent metabolism into bioenergetics models can improve model accuracy and allow fisheries biologists to make more informed decisions regarding fish growth and energetics.