Waterborne 17α-Ethynylestradiol Affects Aggressive Behaviour of Male Fathead Minnows (Pimephales promelas) under Artificial Spawning Conditions

Among fishes, courtship behaviour and nesting defense are strong predictors of reproductive success. We conducted three experiments to assess the impacts of exposure to 17α-ethynylestradiol (EE2) on the ability of male fathead minnows (Pimephales promelas) to establish and defend a spawning territory. Fish were exposed to EE2 (2 or 8 ng L-1) for 27 days, while spawning conditions were gradually optimized. Control (ethanol only) males (C) were paired with treated males (L = low dose, H = high dose) (experiment 1) or individuals from their own treatment group (experiment 2) in competition for a nest site. Solitary males occupied a nest site prior to adding a second male from the same treatment group in experiment 3. Behaviour was quantified from video records. Exposure to EE2 impaired a male’s ability to compete and acquire territories compared to unexposed individuals (experiment 1), but was similar when males were paired with like-treated conspecifics (experiments 2 and 3). Higher levels of overall aggression (aggression rates of both fish) occurred in Cvs.L and Cvs.H than Cvs.C trials (experiment 1). Induction of vitellogenin was significantly higher in exposed fish relative to controls.