Sensory deficits induced by cadmium in banded kokopu, Galaxias fasciatus, juveniles

The potential for cadmium to produce sensory deficits in the mechanosensory lateral line and olfactory systems was examined in migratory Galaxias fasciatus juveniles or 'whitebait'. Using a two-choice chamber apparatus, three groups of whitebait were tested for a known attraction to adult pheromones and then exposed to either 0.1, 0.5 or 1 mug Cd+2 l(-1) for 48 h and retested. The attraction to adult pheromones had been eliminated after exposure to concentrations of 0.5 and 1 mug Cd+2 l(-1), indicating these levels of cadmium exposure had impaired olfactory function. Rheotaxis trials were conducted to determine the level of cadmium exposure which would inhibit lateral line function. The lateral line system was not blocked until a concentration of 2 mug Cd+2 l(-1). The blocking of the lateral line and olfactory sensory systems was reversible. After 14 days recovery in clean freshwater both rheotaxis and the attraction to adult pheromones had returned. Whitebait were also tested for a preference/avoidance response at 2 mug Cd+2 l(-1). Fish showed neither a preference for, or an avoidance of, a concentration which would disable both the lateral line and olfactory sensory systems. The disabling of these sensory systems may render migratory cues undetectable, affecting habitat selection by whitebait, which may ultimately affect the distribution of banded kokopu populations.