Evolution of aerobic energy metabolism in the scombroid fish: Origins of variation in mitochondrial content

Here I investigate the origins of variation in mitochondrial content between two clades of high performance fish within the suborder Scombroidei. This comparative study of muscle bioenergetics in the scombroid fish also provides an opportunity to assess the origins of variation among fiber types in the scombroids.;We have used the mitochondrial enzymes citrate synthase (CS) and cytochrome c oxidase (COX) as biochemical markers for mitochondrial content in striated muscles.;We used CS to examine how these variations in mitochondrial content are regulated by examining constitutive (DNA content) and regulatory (transcription) mechanisms. Within a species, differences in CS activity per gram tissue among fiber types are almost entirely accounted for by gene dosage (DNA content). This indicates that inter-tissue differences in CS activity per gram tissue can be attributed to constitutive expression in combination with differences in myonuclear content. Based upon the relationship between CS mRNA and CS activity, it is likely that most of the interspecies differences are due to post-transcriptional regulation. (Abstract shortened by UMI.).