Larval Deformities Associated with Selenium Accumulation in Northern Pike (<i>Esox lucius</i>) Exposed to Metal Mining Effluent

The objective of this study was to investigate selenium toxicosis in larval northern pike (Esox lucius) originating from reproductively mature pike collected downstream of a uranium milling operation in northern Saskatchewan, Canada. Eggs were obtained from female pike collected from a reference site and three sites representing an exposure gradient (approximately 2, 10, and 15 km downstream of effluent discharge). Embryos were incubated following a two-way (crossover) analysis of variance experimental design that allowed discrimination between effects due to maternal transfer to eggs and effects due to site water exposure in the developing embryos. The major finding of this study was a significant increase in the frequencies of individual deformities (skeletal curvatures, craniofacial deformities, and fin deformities) and edema in fry originating from high and medium exposure site females (mean selenium concentrations of 48.23 and 31.28 μg/g egg dry weight and 38.27 and 16.58 μg/g muscle dry weight, respectively) compared to reference site females. Selenium concentrations resulting in a 20% increase in total deformities above background levels (EC20s) were 33.55 and 21.54 μ/g dry weight in eggs and muscle, respectively. Mathematical conversion of the egg- and muscle-derived relationships to whole body selenium levels resulted in similar EC20s of 15.56 and 17.72 μg/g dry weight, respectively. These relationships between tissue selenium levels and larval deformities suggest that northern pike are within the same range of sensitivity to selenium as the majority of warm water (e.g., centrarchids and cyprinids) and cold water (e.g., salmonids) fish species studied to date.