Oxygen consumption of active rainbow trout, Salmo gairdneri Richardson, derived from electromyograms obtained by radiotelemetry

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Abstract
A radiotelemetry apparatus is described for sensing and transmitting electromyograms (EMGs) from free‐swimming fish. EMGs are recorded from the epaxial muscles of adult rainbow trout during periods in spontaneous (= routine) activity, and forced‐swim, respirometers. When such EMG records are integrated, subjected to spectral analysis, and computer‐averaged, the EMG values (in μV) are highly correlated with the fish oxygen consumption during the activity periods. However, there is a marked difference between the regression slopes for oxygen v. EMG value for the data from the spontaneous, and forced‐swim, respirometers; the former slope is the steeper. The probable explanation of this phenomenon is that whereas in forced swims the epaxial myomeres are responsible for most of the activity of the fish, in spontaneous activity other muscle systems (e.g. of the lateral, dorsal and ventral fins) come to account for a greater relative proportion of body movement. The difference in slope, although great, is evidently a regular phenomenon. The shift from one regression to the other occurs at a fairly precise epaxial EMG value (c. 5 μV). This suggests that the laboratory calibration of EMG value in terms of oxygen consumption can be utilized in the wild so that EMG records from free‐swimming fish, fitted with telemetry packages can be used to deduce oxygen consumption attributable to activity. It also appears that such records can be used as a guide to the type of activity of the fish, i.e. desultory movements or free cruising.