The Metabolic Cost of Maintaining Position for Four North American Stream Fishes: Effects of Season and Velocity

We used a swimming respirometer to measure oxygen consumption (i. e., metabolic cost) of four species of stream fishes while they held position at diferent velocities. We tested naturally acclimatized individuals during spring, summer, fall, and winter at seasonal temperatures and photoperiods. Rosyside dace (Clinostomus funduloides), longnose dace (Rhinichthys cataractae), mottled sculpin (Cottus bairdi), and juvenile rainbow trout (Oncorhynchus mykiss) all showed seasonal changes in oxygen consumption. Seasonal changes in standard metabolic rates seemed to be influenced by changes in reproductive condition as well as ambient temperature. The metabolic cost of maintaining position for rainbow trout and rosyside dace generally increased with velocity. At velocities below eight body lengths per second, longnose dace did not exhibit a significant change in oxygen consumption, because they held position without swimming. At higher velocities, however, long-nose dace swam to maintain their position and oxygen consumption increased rapidly. Mottled sculpin held position without swimming and therefore showed little or no change in energy use with changing current velocity.