THE EFFECTS OF TEMPERATURE AND HYPEROXIA ON ARTERIAL PO2 AND ACID-BASE STATUS IN PIARACTUS-MESOPOTAMICUS

The effects of hyperoxia and change of temperature (range 20-30 degree s C) on blood gases were studied in the teleost fish Piaractus mesopot amicus, native to several major river systems in Brazil. Large hyperox ia-induced increases of arterial PO2 (PaO2) indicated that true branch ial blood shunts are negligible in relation to total gill perfusion. T his implies that blood gases will be influenced by ventilation rather than by shunts. Acute variations of temperature (t) were accompanied b y changes of arterial blood pH (on the average Delta pH(a) Delta t(-1) of -0.015 units degrees C-1), due mainly to alterations of PaCO2:2.4 mmHg at 20 degrees C, 5.0 mmHg at 30 degrees C. Concomitantly, PaO2 de clined from 116 mmHg (20 degrees C) to 89 mmHg (30 degrees C). The dat a suggest that temperature-induced changes of acid-base status depend mainly on gill ventilation and that the decrease of PaO2 with higher t emperature is a result of this regulation. (C) 1997 The Fisheries Soci ety of the British Isles.