Effects of un-ionized ammonia on histological, endocrine, and whole organism endpoints in slimy sculpin (Cottus cognatus)
2008
Spencer, P. | Pollock, R. | Dubé, M.
Ammonia is known to be an important toxicant in aquatic environments. Although ammonia toxicity has been well studied in many fish species, effects of chronic exposure on slimy sculpin (Cottus cognatus), a critical biomonitoring species for northern aquatic habitats, are not well known. Further, with increasing mining development in Canada's north, this information is critical to better predict potential effects of mine effluent discharges on northern fish species. Slimy sculpin were exposed to six concentrations of un-ionized ammonia (NH₃) relevant to concentrations found in northern mining effluents: control (0ppm), 0.278ppm, 0.556ppm, 0.834ppm, 1.112ppm, and 1.668ppm. An LC₅₀ of 1.529ppm was calculated from mortality data. Histopathological examination of gills indicated significant tissue damage, measured as lamellar fusion and epithelial lifting, at 0.834ppm, 1.112ppm, and 1.668ppm. Using gill endpoints, NOEC and LOEC were calculated as 0.556ppm and 0.834ppm, respectively. An EC₅₀ of 0.775ppm was determined for lamellar fusion and an EC₅₀ of 0.842ppm for epithelial lifting. Hemorrhage of gills was present in mortalities, which occurred at 1.668ppm of un-ionized ammonia. A significant decrease in liver somatic index (LSI) was seen in both male and female fish at 0.834ppm and 1.112ppm, respectively. Gonadosomatic index (GSI) in female fish significantly increased at 1.668ppm un-ionized ammonia with an associated significant increase in total wholebody testosterone concentrations. GSI in male fish also significantly increased at 1.668ppm but no differences were seen in testosterone concentrations. No significant differences were seen in gonad histopathological assessments or condition factor. Gill histopathology endpoints may be a more sensitive indicator for detecting effects in slimy sculpin exposed to ammonia than traditional chronic endpoints. Results from this study indicate that ammonia concentrations commonly reported in northern mine effluents hold potential to affect the health of slimy sculpin including acute, chronic, histological and endocrine endpoints.
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