An evaluation of cobalt chloride as an O2-sensitive chemoreceptor stimulant in channel catfish

The effects of cobalt chloride on heart rate, blood pressure, ventilatory frequency and opercular pressure amplitude in channel catfish, Ictalurus punctatus were measured to evaluate the potential of cobalt as a histochemical probe to study mechanisms of oxygen chemoreception, as well as assess the general effects of cobalt on the cardioventilatory physiology of fishes. Cobalt, like cyanide, has been previously used to stimulate oxygen chemoreceptors and hypoxic reflexes in mammals but there is little information on the cardioventilatory effects of cobalt on fish. Catfish were exposed to increasing concentrations (1–20 mg/kg) of cobalt in the water (external) or injections into the dorsal aorta (internal) and the cardioventilatory effects recorded. Mean arterial pressure showed a significant, dose-dependent increase in response to cobalt injections. Heart rate increased slowly, but significantly after cobalt injections but the magnitude of change was not dose-dependent. There was a small increase in ventilatory rate but no effect on amplitude. External cobalt had similar effects but the responses were weaker. Although cobalt stimulated some cardioventilatory reflexes the pattern and magnitude of the responses were noticeably different from those of cyanide and hypoxia. The results suggest that the cardioventilatory reflexes stimulated by cobalt were not mediated by O2-sensitive chemoreceptors and that cobalt is not an effective O2 receptor stimulant in fishes.