Tissue-Specific Cytochrome Oxidase Activity in Largemouth Bass: The Metabolic Costs of Feeding and Growth

Abstract

Changes in relative tissue size and cytochrome c oxidase (CCO) activity owing to growth rate (ration size) are described for the largemouth bass (Micropterus salmoides) and interpreted as a response to the cumulative demands of specific dynamic action (SDA). CCO activity, an aerobic enzyme reflecting metabolic capacity, was significantly correlated with growth rate for all tissues combined (whole body). The influence of increased relative liver size with increased growth rate was negated by decreased CCO/g. Increases in relative size and CCO activity were observed for muscle and may reflect a cost for growth in this tissue-increased swimming activity did not affect muscle CCO activity. Relative gastrointestinal (GI) size and CCO activity/g were influenced by growth rate, with total GI CCO contributing as much as 30% of whole-body CCO activity. Growth efficiency was highest when total GI CCO activity, as a percentage of whole-body CCO, was highest; i.e., when relative "processing" capability was the greatest. In fish that lost weight, brain CCO activity/g was significantly reduced, and total liver CCO activity was a higher proportion (15%) of whole-body CCO activity. Compensation by the heart for increased demand was accomplished by ventricular hypertrophy. Relative heart size, which was significantly correlated with growth rate, may be useful for studying the metabolic capacity of wild populations of fish. These results suggest that, in the largemouth bass, the SDA response is largely due to increases in GI and muscle metabolism.