THE SO-CALLED TONIC MUSCLE-FIBER TYPE IN CYPRINID AXIAL MUSCLE - THEIR MORPHOLOGY AND RESPONSE TO ENDURANCE EXERCISE TRAINING

The morphology and the effect of an endurance training programme on to nic muscle fibres were studied in chub Leuciscus cephalus, by means of histochemistry and immunohistochemistry, electronmicroscopy and morph ometry/stereology. Location and distribution, SDH- and mATPase-activit y, reaction to an anti-tonic myosin antibody and ultrastructural featu res of the fibre type were investigated. With regard to training condi tions, fibre size was not significantly affected. However, an increase in the volume densities of mitochondria, lipid and myofibrils can be observed, suggesting a training influence on the aerobic capacity of t he so-called tonic muscle fibres. Based on the quantitative findings, the fine structure and the response to training, similarities with int ermediate muscle fibres and the functional role of these so-called ton ic muscle fibres are discussed. (C) 1997 The Fisheries Society of the British isles.