THE EFFECTS OF TEMPERATURE ON OXYGEN-UPTAKE, GILL VENTILATION AND ECGWAVE-FORMS IN THE NILE TILAPIA, OREOCHROMIS-NILOTICUS

Oreochromis niloticus were acclimated to 35 (group I) and 15 degrees C (group II). In group I, the temperature was decreased from 35 to 15 d egrees C, followed by return to 35 degrees C, while iq group II, the t emperature rose to 35 and returned to 15 degrees C. For each temperatu re, oxygen uptake ((V) over dot O-2), gill ventilation ((V) over dot ( G)) and electrocardiograms were obtained. Curves were identical and fo r the two groups were without hysteresis. Increases of (V) over dot (G )/(V) over dot O-2 with rising temperature kept O-2 extraction relativ ely constant. Heart rate increased with temperature. The QRS and the T wave amplitudes were constant, while QRS and ventricular action poten tial duration increased at low temperature. (C) 1998 Elsevier Science Ltd. All rights reserved.