The effects of temperature on oxygen uptake, gill ventilation and ecg waveforms in the nile tilapia, Oreochromis niloticus

Oreochromis niloticus were acclimated to 35 (group I) and 15°C (group II). In group I, the temperature was decreased from 35 to 15°C, followed by return to 35°C, while in group II, the temperature rose to 35 and returned to 15°C. For each temperature, oxygen uptake ( V ̇ O 2), gill ventilation ( V ̇ G) and electrocardiograms were obtained. Curves were identical and for the two groups were without hysteresis. Increases of V ̇ G/ V ̇ O 2 with rising temperature kept O 2 extraction relatively constant. Heart rate increased with temperature. The QRS and the T wave amplitudes were constant, while QRS and ventricular action potential duration increased at low temperature.