The cortisol stress response in male round goby (Neogobius melanostomus): effects of living in polluted environments?

Acute exposure to contaminants frequently induces stress, but prolonged exposures, such as those experienced by individuals in wild populations, can impair the capacity to mount a stress response. Using the round goby (Neogobius melanostomus), a small benthic fish and potential sentinel species for habitat contamination in the Great Lakes, we explored the impacts of living in highly polluted areas. Round goby were collected from highly contaminated and less contaminated areas of Hamilton Harbour (a well-known site of polycyclic aromatic hydrocarbon (PAH) and heavy metal contamination). The cortisol stress responses of fish from sites of high and low contamination were compared using an EIA assay on blood collected (n = 112) either prior to or 0, 10, 30, 60, 240 min and 24 h following the application of a 4-min confined air exposure stressor. Plasma cortisol levels were elevated at 10 and 30 min post-stressor (100.3 and 87.5 ng/mL), and returned to levels similar to baseline (22.3 ng/mL) 1 h after the stressor. In contrast to predictions, round goby from areas of high and low contamination had similar cortisol levels at all timepoints. We also monitored stress responses immediately after a chasing stressor (n = 19). During the chasing stressor, contaminated-site round goby exhausted faster than individuals from a less contaminated site, although they had similar levels of plasma cortisol (23.5 versus 20.9 ng/mL) and lactate (2.53 versus 1.98 mmol/L). Our results indicate that not all fishes may demonstrate impaired stress responses, even in highly contaminated habitats; however, such animals may still have increased vulnerability to predation.