Physiological stress response of Mountain Whitefish (Prosopium williamsoni) and White Sucker (Catostomus commersoni) sampled along a gradient of temperature and agrichemicals in the Oldman River, Alberta

Abstract

Species differences in tolerance to environmental stressors can contribute to differences in species distribution and abundance along river gradients. Climate change and intensive agriculture are likely to have major effects on fish populations in temperate zones, yet understanding of the interactions between temperature and chemical stressors on fish physiology is limited. The objective of this study was to compare the stress responses of the Mountain Whitefish, (Prosopium williamsoni, a cold-water fish) and White Sucker (Catostomus commersoni, a cool-water fish), along a temperature and pesticide gradient in the Oldman River, Southern Alberta in spring and summer. Fish were seined, placed into an enclosure, and plasma cortisol, glucose, liver glycogen, and condition factor were measured. Plasma acetylcholinesterase (AChE) activity was used as an indicator of exposure to organophosphate and carbamates pesticides. Whitefish had lower plasma AChE activity and lower liver glycogen reserves compared to suckers at all sites and all sampling times but the differences in plasma cortisol were not species-specific and there were no differences in plasma glucose levels, except at one site. Plasma cortisol increased, and plasma glucose decreased along a downstream river gradient in whitefish in both spring and summer; in sucker only plasma cortisol fluctuated and only in the summer. Liver glycogen decreased along the river gradient in both species at both seasons. Our study detected important species-specific differences in AChE activities and responses of the physiological stress axis, suggesting that whitefish are more sensitive to temperature and pesticide stress than suckers.