The effects of zinc on the cardiac and ventilatory rhythms of rainbow trout ( Salmo Gairdneri, Richardson) and their responses to environmental hypoxia

Recordings were made of the cardiac and ventilatory rhythms of rainbow trout subjected to solutions of 40 and 10 ppm zinc in an experimental circulation. The higher concentration produces clearly-defined increases in ventilatory and coughing frequency and a decrease in heart rate; the percentage coupling between the two rhythms usually increased. During exposure to 10 ppm added zinc the effects are not so readily discernible but are comparable in type. The addition of 10 ppm zinc has a significant effect on the responses of rainbow trout to hypoxia before and after this treatment. It is concluded that zinc interferes with some of the mechanisms involved in the uptake of oxygen at the gills and consequently can significantly affect the ability of fish to respond to the additional stress of oxygen lack in its environment.