Anoxic depression of spontaneous locomotor activity in crucian carp quantified by a computerized imaging technique

The crucian carp (Carassius carassius L.) is one of the most anoxia-tolerant fishes. An important strategy used by the crucian carp to survive anoxia is to lower its rate of energy consumption. Anoxia- tolerant fish are known to utilize simultaneously two different strategies for reducing energy consumption during anoxia, the first being a reduction in locomotor activity and the second being a depression of cellular energy demands. Nevertheless, the reduction in locomotor activity during anoxia has never been measured quantitatively. This lack of information is apparently because technical problems have prevented the measurement of spontaneous locomotor activity in fish. It is now possible to use computerized video-imaging techniques to record the movement of an animal continuously. By the use of such a technique, we show that crucian carp respond to anoxia (330 min at 9°C) by rapidly decreasing their locomotor activity (spontaneous swimming distance) to about 50 % of that displayed during normoxia. Frequency diagrams of spontaneous swimming speed showed no bimodality and indicated a general decrease in swimming speed from a median value of 1.82 m min-1 during normoxia to 0.82 m min-1 during anoxia. It is tentatively estimated that the anoxic depression of locomotor activity corresponds to a 35–40 % reduction in total energy consumption. The role of locomotor activity in fish energy budgets is discussed.