Diazinon disrupts antipredator and homing behaviors in chinook salmon (Oncorhynchus tshawytscha)

Neurotoxic pesticides are known to contaminate surface waters that provide habitat for salmonids, including some listed for protection under the U.S. Endangered Species Act. Despite their widespread use, the impacts of these pesticides on the neurological health of wild salmon are not well understoo d. Of particular concern are the organophosphate and carbamate insecticides that block synaptic transmission by inhibiting neuronal acetylcholinestera se. Here we assess the effects of diazinon, an organophosphate insecticide, on alarm pheromone induced antipredator responses and homing behavior in c hinook salmon (Oncorhynchus tshawytscha). Nominal exposure concentrations ( 0.1, 1.0, and 10.0 mu g.L-1) were chosen to emulate diazinon pulses in the natural environment. In the antipredator study, diazinon had no effect on s wimming behavior or visually guided food capture. However, the pesticide si gnificantly inhibited olfactory-mediated alarm responses at concentrations as low as 1.0 mu g.L-1. Similarly, homing behavior was impaired at 10.0 mu g.L-1. Our results suggest that olfactory-mediated behaviors are sensitive to anticholinesterase neurotoxicity in salmonids and that short-term, suble thal exposures to these insecticides may cause significant behavioral defic its. Such deficits may have negative consequences for survival and reproduc tive success in these fish.