Interactive effects of wastewater effluent and hypoxia on the metabolic physiology and health of mummichog killifish (Fundulus heteroclitus)

Abstract

Hypoxia often occurs in aquatic ecosystems that receive effluent from municipal wastewater treatment plants (WWTP). WWTP effluent contains contaminants that could disrupt the complex physiological pathways fish use to cope with hypoxia (e.g., pharmaceuticals, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons), but the effects of WWTP effluent on the physiological responses of fish to chronic hypoxia is poorly understood. We exposed mummichog killifish (Fundulus heteroclitus) to hypoxia (5 and 2 kPa O2) and/or WWTP effluent for 21 days in a full factorial design. We then measured hypoxia tolerance, whole-animal metabolism, gill morphology, haematology, and tissue metabolites. In clean water, killifish responded to chronic hypoxia with improvements in hypoxia tolerance – increases in time to loss of equilibrium at 0.5 kPa (tLOE) and decreases in critical O2 tension (Pcrit) – in association with increased gill surface area as a result of regression of the interlamellar cell mass (ILCM). Concurrent exposure to wastewater attenuated the increases in tLOE and gill remodeling in chronic hypoxia, and nearly depleted brain glycogen stores. Therefore, exposure to WWTP effluent can disrupt the physiological mechanisms fish use to cope with chronic hypoxia and impair hypoxia tolerance. My research suggests that the combination of stressors near WWTPs can have interactive effects on the physiology and health of fish.