The Effect of Synthetic Estrogen on Foraging and Predator Avoidance in the Common Roach (Rutilus rutilus)

Abstract: Synthetic estrogens that originate mainly from oral contraceptive pills reach our waters through sewage effluent and potentially affect organisms in the natural environment. This study focused on the effects of the synthetic estrogen 17-alpha-ethinylestradiol (EE2) on the foraging and predator avoidance behaviors of the planktivorous fish roach (Rutilus rutilus), a common fish in Swedish lakes and rivers. To assess the effects of EE2, roach were exposed in aquariums to environmentally relevant water concentrations of EE2 at 0, 0.5, 5 and 50 ng/l for 3 weeks. They were then taken out for foraging trials where their foraging on the plankton Daphnia magna was quantified. Foraging trials were made both with and without predator cues from pike (Esox lucius) to assess predator avoidance behavior in the roach. Results showed that foraging of roach on D. magna significantly increased at the highest concentration of EE2, compared to control, and this may be due to increased metabolic rate from the synthetic estrogen, or a higher energy demand due to induced detoxification mechanisms in the roach. No significant effect of the EE2 on predator avoidance behavior could however be discerned. Increased foraging of planktivorous fish on zooplankton could potentially have an effect on ecosystem balance in lakes and rivers.