Endurance exercise training in the fast and slow muscles of a teleost fish (Pollachius virens)

Abstract

1. The recruitment of muscle fibre types has been investigated in the coalfish (Pollachius virens) using electromyography. Red trunk muscles were active at all swimming speeds examined (0.25–3.6 lengths/s). Interestingly, white fibres were recruited at 0.8–2.0 lengths/s providing evidence that this muscle type is also used during sustained activity. 2. The effect of endurance exercise training on muscle fibre size and enzymes of energy metabolism has also been investigated. Fish were exercised continuously at 2.1 lengths/s for a period of three weeks in an experimental swimming chamber. This swimming speed represents a significant increase in work load relative to non-exercised fish as evidenced by muscle fibre hypertrophy and an increase in creatine kinase activities in both red (184%) and white (260%) muscles. 3. Glycogen storage levels increased to a greater extent in red (+520%) than white (+200%) muscles. Phosphofructokinase activity was eight times higher in the red muscle of exercised fish. In contrast, there was only a small increase in citrate synthetase (+30%) and no change in either hexokinase or cytochrome oxidase activities in the red muscle of trained fish. 4. Increased hydroxyacyl CoA dehydrogenase activities in both muscle types indicate an enhanced capacity for fatty acid catabolism with training. 5. White muscle phosphofructokinase activities were not significantly different in trained and untrained fish. It is likely that the maximum potential of white muscle for anaerobic glycogenolysis is already sufficient to meet all its energy requirements at this swimming speed. 6. The results suggest that the capacity of coalfish red muscle to do aerobic work remains essentially unchanged by endurance exercise training and that any increase in the ability to produce ATP must be met anaerobically.