Juveniles of the zooplanktivorous Danube bleak (Chalcalburnus chalcoides mento) and of the benthivorous nase (Chondrostoma nasus) were subjected to an endurance training regime for 81–90 d. Growth performance was better in trained than in untrained Danube bleak but not in nase. Mass specific heart size was significantly greater in trained than in untrained C. nasus, but no difference was found in C. chalcoides. The size of muscle fibres increased with training in both species; in nase the red and pink fibres and in Danube bleak the red and white fibres exhibited the most conspicuous response. Mass specific activities of the enzymes of energy metabolism were generally not affected by training, but in the white fibres of C. chalcoides, three glycolytic enzymes displayed a parallel trend indicating an increase of the glycolytic potential with training of about 25%. Since the Danube bleak maintains an irregular, burst-like mode of swimming even under the endurance training regime, we assume the lactate produced intermittently in the white muscles to be oxidized in the heart and the red muscles. The activities of three glycolytic heart enzymes were up to 25-fold higher in C. chalcoides than in C. nasus.
Energy metabolism in single human muscle fibres during intermittent contraction with occluded circulation.