Date of Submission


Document Type


Degree Name

Master of Science in Environmental Science


Biology and Environmental Sciences


John Kelly

Committee Member

Steve McCormick

Committee Member

Roman Zajac


Prednisolone--toxicity, Salmo salar--growth & development


Adrenocortical hormones, Atlantic salmon


The smolting process that many anadromous salmonids undergo prior to migration is largely mediated by release of the corticosteroid cortisol, which serves to alter osmoregulatory physiology and prepare the fish to move from freshwater into seawater. The synthetic corticosteroid prednisolone mimics the effects of cortisol and is widely used as a potent antiinflammatory medication. Prednisolone has been detected in measurable concentrations of some freshwater systems. It is possible that environmental concentrations of prednisolone may negatively impact salmonids, by altering parr physiology or interfering with secondary measures of performances associated with smoltification.

Forty-eight Atlantic salmon parr of similar length (10.1 cm fork length, SD = 0.5) were split into four groups of 12 fish and individually PIT tagged. Treatments consisted of implantation of hormones dissolved in vegetable oil: a) 2.5 μg/g prednisolone, b) 25 μg/g prednisolone, c) 25 μg/g cortisol, or d) vegetable oil (control). Fish were held for 22 days in two mixed group holding tanks, at ambient temperatures and natural day length, and fed ad libitum. Individuals were sacrificed, measured (length/weight), and gill filaments, plasma, and liver samples were collected. Concentrations of plasma chloride, glucose and cortisol, gill NKA activity, hematocrit, and overall growth rate were determined. Suppression of growth was observed with 25 μg/g prednisolone and 25 μg/g cortisol. Increase in Igfbp-1a1 mRNA expression was observed in the 25 μg/g prednisolone treatment. Plasma chloride was significantly higher in the 25 μg/g prednisolone treatment compared to the control. Results indicated that exposure of Atlantic salmon parr to prednisolone had a significant effect on growth and osmoregulation, suggesting that this hormone may act as an endocrine disrupting chemical in the aquatic environment.


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