Power production during steady swimming in largemouth bass and rainbow trout.

Steady swimming in fishes is powered by the aerobic or red muscle, but there are conflicting theories on the relative roles of the anterior and posterior red muscle in powering steady swimming. To examine how red muscle is used to power steady swimming in rainbow trout (Oncorhynchus mykiss), electromyographic (EMG) and sonomicrometry recordings were made of muscle activity in vivo. These data were used in in vitro work-loop studies of muscle power production. Data on in vitro power production were also collected for largemouth bass (Micropterus salmoides) red muscle from previously published data on in vivo muscle activity. The in vivo data collected from swimming trout were similar to those for other species. The anterior red muscle of these fish has the longest duty cycle, the smallest phase shift between the onset of EMG activity and maximum muscle length during each tailbeat and undergoes the smallest strain or length change. For both trout and largemouth bass, work-loop experiments indicate that the majority of power for steady swimming is generated by the posterior muscle, as has been observed in other species.