Sustained swimming speeds and myotomal muscle function in the trout, Salmo gairdneri

Rainbow trout were trained for 3–4 weeks in a flume at swimming speeds of 1, 2 and 3 l s −1 . For each experiment growth rates were estimated and by measuring the hypertrophy of red and mosaic skeletal muscle fibres their function was described at particular swimming speeds and compared with earlier experiments on coalfish using the same technique. Maximum growth, compared with controls in still water, occurred at swimming speeds of 1 l s −1 . At this speed the trout mosaic muscle fibres hypertrophied by 40% but the red muscle fibres showed only a 25% hypertrophy. It is suggested that natural swimming speeds are close to 1Ls −l and the trout mosaic fibres are better adapted for use at this speed in comparison with coalfish white muscle fibres.