RESPIRATORY AND ACID-BASE DISTURBANCES IN RAINBOW-TROUT BLOOD DURING EXPOSURE TO CHLORAMINE-T UNDER HYPOXIA AND HYPEROXIA

Rainbow trout Oncorhynchus mykiss were exposed acutely to chloramine-T at a therapeutic concentration (9 mg l(-1)) under moderately hypoxic (water Po-2: 100 mmHg) or hyperoxic (water Po-2: 430 mmHg) conditions and arterial blood gas tensions (Pao(2) and Paco(2)) and pH were monit ored using an extracorporeal circulation. Hypoxia, alone, resulted in an increased ventilation frequency, a decrease in both arterial Pco(2) and PO2 and an increase in arterial pH. There was no effect of chlora mine-T exposure on the measured variables as compared with pre-exposur e (hypoxia baseline) values. Hyperoxia, alone, resulted in a decrease in ventilation frequency, an increase in arterial Pco, and Po-2 and a decrease in arterial pH. Chloramine-T exposure under these conditions caused a significant increase in ventilation frequency, but no signifi cant effect on arterial blood gases or pH as compared with the hyperox ia baseline values. Despite the increase in ventilation caused by chlo ramine-T during hyperoxia, there was no reduction in Pco(2) or increas e in Po-2. Although these results were of little pathological signific ance this study suggests that chloramine-T, although stimulating venti lation, was impairing the diffusion of CO2 across the gill probably by the secretion of branchial mucus and enhancing the gill boundary laye r. (C) 1997 The Fisheries Society of the British Isles.