On The Function of the White Muscles in Teleosts at Intermediate Swimming Speeds

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Abstract
1. The swimming performance of rainbow trout, Salmo gairdneri, and the electrical activities, recorded extracellularly, of its red and mosaic muscles have been studied at different swimming speeds. 2. A linear relationship was found between the specific velocity (body lengths/sec) and the frequency of tail beating at frequencies up to 5/sec. 3. The red muscles are active at all swimming speeds at which the fish swim by tail oscillations. Discharges from this muscle decrease in duration with frequency up to 3.5-5.0 beats/sec and then increase while the interburst interval decreases linearly with tail-beat frequency. 4. Mosaic muscle becomes active at 3.05-3.60 tail beats/sec and increases slightly with increasing frequency of tail oscillations. Greatly increased activity was recorded in response to struggling and rapid accelerations. 5. The white (mosaic) muscle mass of teleosts is concluded to be involved at intermediate swimming speeds and to be active at the higher range of cruising speeds.