The Effect of Prolonged Exercise on the Lateral Musculature of the Brown Trout (<i>Salmo Trutta</i>)

Abstract

ABSTRACT Hatchery-reared brown trout (Salmo trutta L.) were exercised continuously for periods of several weeks at swimming speeds of 1·5, 3·0 and 4·5 body lengths/s and their rates of growth were determined. Changes in the major muscle constituents were determined by biochemical analysis and changes in muscle cells using histochemistry and electron microscopy. At the lowest speed the fish grew much more rapidly, and converted food into fish flesh much more efficiently than their controls kept in still water. Large stores of glycogen and lipid were built up. Gross changes were observed mainly in red muscle cells, with enlargement of the mitochondria being very noticeable. The fish swimming at intermediate speed showed greater growth than the controls, although the energy expended in swimming against the water current led to an inefficient food conversion rate. Large stores of glycogen were built up, but lipid levels fell, suggesting that this was the major fuel for swimming at this speed. Changes in all the muscle fibre types were observed. The energy required to maintain the fish in the water flow at the highest speed was so great as to have serious detrimental effects on the fish, and many did not survive. Those which did survive showed signs of gross depletion.