Sectioning the first four pairs of spinal nerves prevents the large increase in circulating catecholamine concentrations seen in Atlantic cod swimming at their critical velocity (Ucrit). There is also a significant reduction in the swimming performance of the fish. To test whether this reduced performance results from the lack of increase in plasma catecholamine levels or from the fact that other organs are also denervated by the operative procedure, a mixture of adrenaline and noradrenaline was infused into swimming, denervated fish. This caused a significant increase in their Ucrit. It is concluded, therefore, that the rise in plasma catecholamine levels seen in Atlantic cod swimming at their maximum sustainable velocity enhances the swimming performance of these fish.

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