The use of opercular muscle electromyograms as an indicator of the metabolic costs of fish activity in rainbow trout, Salmo gairdneri Richardson, as determined by radiotelemetry

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Abstract
Averages of electromyogram (EMG) signals emanating from the levator arcus palatini, a small muscle involved in the operation of the operculum in rainbow trout, Salmo gairdneri, were analysed in terms of their relationship to the fish's oxygen consumption rates under various activity levels. The EMG signals were detected and transmitted with a radio‐telemetry system. The EMG values showed a good correlation with corresponding oxygen consumption rates for fish under forced‐swimming conditions but not when the fish was swimming spontaneously; this is attributed to an ability to regulate oxygen uptake at the gill surfaces by other means than increasing the ventilation volume, including alterations in the gill blood flow dynamics (e.g. secondary lamellar recruitment), and changes in the cardiac output. Under forced‐swim conditions, where the oxygen demands by the respiring muscles were higher, increased ventilation volume, as indicated by increased opercular muscle activity, was directly related to swimming speed and oxygen uptake.