Sub-lethal effects of a neonicotinoid, clothianidin, on wild early life stage sockeye salmon (Oncorhynchus nerka).

One of the categories of environmental contaminants possibly contributing to declining sockeye salmon (Oncorhynchus nerka) in the Fraser River, British Columbia, Canada is pesticides. In this 4-month study, the effects of environmentally relevant concentrations of a waterborne neonicotinoid, clothianidin (0.15, 1.5, 15 and 150 µg/L), on embryonic, alevin and early swim-up fry sockeye salmon derived from four unique genetic crosses of the Pitt River, BC stock were investigated. There were no significant effects of clothianidin on survival, hatching, growth or deformities, although genetic variation significantly affected these endpoints. Clothianidin caused a significant 4.7-fold increase in whole body 17ß-estradiol levels in swim-up fry after exposure to 0.15 µg/L, but no effects were observed on testosterone levels. In addition, hepatic expression of the gene encoding glucocorticoid receptor 2 was also impacted at the highest concentration of clothianidin tested, and was found to be ∼4-fold lower compared to the sockeye reared in control water. These results indicate additional examination of clothianidin and its effects on salmonid gonad development and the reproductive and stress endocrine axes in general, is warranted.