Partitioning of Energy in Fish: Can Reduction of Swimming Activity Compensate for the Cost of Production?

1. By using a new video activity monitoring processor (Kaufmann, 1983) in conjunction with a large respirometer, we have measured swimming activity, oxygen consumption and reproductive investment (in the form of gonadal growth) of roach (Rutilus rutilus L.) during a seasonal cycle. 2. If the effect of temperature on metabolism is taken into account it can be shown that swimming activity is drastically reduced during the period of gonadal synthesis (July-December). 3. On the basis of a calibration curve established for the preproductive phase (January—June), the reduction in locomotor activity is estimated to represent a saving of 1485 kj kg" of metabolizable energy during a period in which 364 kj worth of gonadal tissue per kg of fish are being synthesized. 4. Our data provide the first evidence that even in a poikilothermic animal reduction of locomotor activity may compensate for the costs of producing gonadal tissue.