Cadmium disrupts behavioural and physiological responses to alarm substance in juvenile rainbow trout (Oncorhynchus mykiss)

Alarm substance is a chemical signal released from fish skin epithelial cells after a predator causes skin damage. When other prey fish detect alarm substance by olfaction, they perform stereotypical predator-avoidance behaviours to decrease predation risk. The objective of this study was to explore the effect of sublethal cadmium (Cd) exposure on the behavioural and physiological responses of juvenile rainbow trout (Oncorhynchus mykiss) to alarm substance. Waterborne exposure to 2 mug Cd l(-1) for 7 days eliminated normal antipredator behaviours exhibited in response to alarm substance, whereas exposures of shorter duration or lower concentration had no effect on normal behaviour. Furthermore, dietary exposure to 3 mug Cd g(-1) in the food for 7 days, which produced the same whole-body Cd accumulation as waterborne exposure to 2 mug l(-1), did not alter normal behaviour, indicating that an effect specific to waterborne exposure alone (i.e. Cd accumulation in the olfactory system) results in behavioural alteration. Whole-body phosphor screen autoradiography of fish exposed to Cd-109 demonstrated that Cd deposition in the olfactory system (rosette, nerve and bulb) during waterborne exposure was greater than in all other organs of accumulation except the gill. However, Cd could not be detected in the brain. A short-term elevation in plasma cortisol occurred in response to alarm substance under control conditions. Cd exposures of 2 mug g(-1) waterborne and 3 mug g(-1) dietary for 7 days both inhibited this plasma cortisol elevation but did not alter baseline cortisol levels. Our results suggest that exposure to waterborne Cd at environmentally realistic levels (2 mug l(-1)) can disrupt the normal behavioural and physiological responses of fish to alarm substance and can thereby alter predator-avoidance strategies, with potential impacts on aquatic fish communities.