Long‐term water quality data explain interpopulation variation in responsiveness to stress in sticklebacks at both wastewater effluent‐contaminated and uncontaminated sites

The magnitude of the corticosteroid response to a standardized stressor varied in proportion to the concentration of effluent in three‐spined sticklebacks ( Gasterosteus aculeatus L.) captured downstream of 10 wastewater‐treatment plants (WWTPs). However, at 9 sites with no upstream WWTP input interpopulation variation in the reactivity of the stress axis occurred across a similar range to that seen for fish at impacted sites, suggesting that the factor(s) responsible for modulating stress responsiveness in sticklebacks is not unique to sites receiving WWTP effluent. Physicochemical data from a long‐term monitoring program were employed to investigate whether variation in water quality contributed to between‐site variation in stress axis reactivity. Between‐site variation in 14 water quality determinands explained between 30% and 60% of the variation in stress reactivity and fish size for sticklebacks at both WWTP–contaminated and uncontaminated sites. At uncontaminated sites the mean mass and length of sticklebacks increased with total oxidized nitrogen (N) concentration (as an indicator of anthropogenic input), whereas at WWTP–contaminated sites fish size decreased with increasing effluent concentration, suggesting that factors adversely affecting growth were present predominantly at WWTP–contaminated sites. In contrast, at both contaminated and uncontaminated sites the magnitude of the corticosteroid response to a standardized stressor increased with anthropogenic input (effluent concentration or total oxidized N, respectively), indicating that a factor or factors modulating the reactivity of the stress axis may be present at both WWTP–contaminated and uncontaminated sites. Environ Toxicol Chem 2016;35:3014–3022. © 2016 SETAC