In situ activity metabolism of rainbow trout (Oncorhynchus mykiss): Estimates obtained from telemetry of axial muscle electromyograms

Activity metabolism of free-swimming rainbow trout (Oncorhynchus mykiss) was estimated using electromyogram telemetry of the axial muscle. Estimates were obtained for five fish for temperatures ranging from 3 to 22 degrees C. Activity metabolism was divided by standard metabolism to produce a relative metabolic cost of activity (RMA). The average diel pattern of RMA was predominantly crepuscular. RMA increased at dawn and then slowly increased to an average maximum peak of 1.8 at dusk. After dusk, RMA slowly declined to a minimum value of 1.4 just prior to dawn. The diel pattern was similar over most of the temperature range studied, but became less distinct at the upper and lower limits of the range. Changes in mean daily RMA were strongly correlated with changes in mean temperature. Mean RMA of the five fish sampled over three seasons was 1.5, with very little variation among fish. The results of this study indicate that the activity metabolism of free-swimming rainbow trout is less than twice standard.