Sublethal Effects of Elevated Nitrate on Atlantic Salmon, Salmo salar

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Freitag, Alyssa Rose
Atlantic salmon; Development; Effect of chemicals on; Nitrates; Physiological aspects.; Marine Biology
thesis / dissertation description
As the end product of nitrification, nitrate (NO3-) can accumulate to alarming concentrations in aquatic ecosystems, especially in areas with extensive farming and aquaculture activity. Nitrate contamination has been overlooked in the past, but recent evidence suggests that elevated NO3- can alter both reproductive status and thyroid function in a number of animal models. This study examines a variety of physiological and developmental responses to elevated NO3- by Atlantic salmon, Salmo salar L. 1758. Embryos were exposed to 3.76 and 93.15 mg L-1 NO3-N to determine the effects of NO3- on thyroid development. The data revealed no significant differences in number of thyroid follicles, average follicular lumen volume, or total luminal volume, suggesting that elevated NO3- does not impact the morphology of early thyroid tissue in S. salar. In a second experiment, juvenile S. salar were exposed to 5.2, 10.3 and 101.8 mg L-1 NO3-N for 27 days. Chronic exposure to elevated NO3- did not induce significant changes in plasma concentrations of 11-ketotestosterone, total thyroxine or total triiodothyronine, but plasma testosterone displayed a highly significant, non-monotonic dose response to increasing concentrations of NO3-N. Plasma testosterone was elevated at 10.3 mg L-1 NO3-N, which is the maximum allowable contaminant level for NO3-N in drinking water. This data confirms that elevated NO3- can alter hormone production, metabolism and/or clearance, and highlight the importance of NO3- management. These results can be applied to both natural aquatic ecosystems and aquaculture operations, and can be used to create new water quality criteria for the culture of S. salar.