Maximal rates of oxygen consumption in vitro have been measured under standardized conditions at three test temperatures (5 ~ 15 ~ 25 ~ on minced preparations of red muscle from l0 species of shallow-water marine teleost fishes. These fishes came from three different geographic areas, two with cool average water temperatures (near 15 ~ coastal southern California, Gals Islands) and one with warm average water temperatures (near 25~ Hawaiian Islands). The group is made up of post-juvenile or adult epipolagic fishes, which are moderately or very active in terms of their locomotor activities. A large part of the range of phylogenetic diversity among the tcleosts is represented, as is the body weight range from a few grams to several kilograms. The purpose of the work is to provide part of a set of tissue-metabolism data on shallowwater fishes for future comparison with similar results from deep-sea species. Of 8 complete curves for oxygen uptake rate versus temperature (R-T curves), 6 are normal in shape ( Q10 -~ i.5), t is normal but with a low Q~0, and ~ is p.artly fiat, partly normal. The differences between the species in terms of both absolute positions and slopes of the R-T curves are not related in any consistent way to any of the three testable variables: phylogenetic position, long-term adaptation temperature, and body size. The red muscles of a variety of adult epipolagic fishes, at ecologically realistic temperatures, are shown to be exceptions to the general rule that tissues of ectothermous lower vertebrates have lower metabolic rates than comparable tissues of non-torpid endothermons higher vertebrates. This circumstance probably is a major factor in the great capacities for sustained high-speed swimming shown by most epipolagic fishes. Other physiological and ecological implications of the results are discussed.