METABOLIC-RATE AND LEVEL OF ACTIVITY DETERMINED IN TILAPIA (OREOCHROMIS-MOSSAMBICUS PETERS) BY DIRECT AND INDIRECT CALORIMETRY AND VIDEOMONITORING

In order to correlate the metabolic rate and locomotor activity level of fish, a calorimetric system (Setaram GF 108) was supplemented with a video tracking and motion analysis system. The motion analysis syste m is based on digital image processing. Once every second, two images (with an interval of 120 ms) are digitized and subtracted. The differe nce between the two images is used as a measure of the animal's moveme nt. The activity of different complex movements, like turning, acceler ations, fin movements, and branchial ventilation, were thus quantified , The combination of motion analysis with calorimetry gave some intere sting results, Firstly, during extreme hypoxia, tilapia does not becom e lethargic as has been described for the anoxia-tolerant crucian carp [1]. The locomotor activity level during severe hypoxia corresponded to the locomotor activity level during normoxia in the restricted area of the calorimetric vessel. This implies that the calorimetrically de termined reduction of the heat flux by 50% under these conditions can be ascribed to a reduction in the cellular energy metabolism - metabol ic depression. Secondly, the metabolic rate under constant light condi tions was elevated from 11-18%, and the animals showed strong fluctuat ions in the heat flux; periods of aerobic metabolism alternated with p eriods of anaerobic metabolism. This was in contrast to the experiment s under constant dark conditions in which the metabolic rate was aroun d the standard metabolic rate (SMR). Under the applied conditions, no correlation was observed between heat production measurements and loco motor activity. This may possibly be ascribed to the limited size of t he calorimetric vessel in which the animals' metabolic rates were arou nd SMR. The observed oscillations in metabolic rate under light condit ions could be another disrupting factor; oscillations in the circulati on and ventilation could be responsible for this phenomenon.