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 (9mg l^?1) under moderately hypoxic (water P o₂: l00 mmHg) or hyperoxic (water P o₂: 430mmHg) conditions and arterial blood gas tensions ( P ao₂ and P aco₂) and pH were monitored using an extracorporeal circulation. Hypoxia, alone, resulted in an increased ventilation frequency, a decrease in both arterial P co₂ and P o₂ and an increase in arterial pH. There was no effect of chloramine-T exposure on the measured variables as compared with pre-exposure (hypoxia baseline) values. Hyperoxia, alone, resulted in a decrease in ventilation frequency, an increase in arterial P co₂ and P o₂, and a decrease in arterial pH. Chloramine-T exposure under these conditions caused a significant increase in ventilation frequency, but no significant effect on arterial blood gases or pH as compared with the hyperoxia baseline values. Despite the increase in ventilation caused by chloramine-T during hyperoxia, there was no reduction in P co₂ or increase in P o₂. Although these results were of little pathological significance, this study suggests that chloramine-T, although stimulating ventilation, was impairing the diffusion of co₂ across the gill probably by the secretion of branchial mucus and enhancing the gill boundary layer.