|dc.description.abstract||Adequate levels of dissolved oxygen (DO) are essential to the health of most aquatic organisms. While diel fluctuations in DO concentration are a normal occurrence in aquatic ecosystems, anthropogenically-produced periods of prolonged hypoxia have the potential to cause changes in growth, reproduction and behaviour in animals. My thesis examined reproductive behaviour and physiology of fathead minnows (Pimephales promelas) following exposure to several concentrations of dissolved oxygen. Using a custom-built system that was able to maintain DO concentrations at precise levels, reproductive performance was analyzed under 3.5 mg/l, 4.5 mg/l, 5.5 mg/l and a control of 7.5 mg/l of DO. A second experiment evaluated reproductive performance at 5.0, 5.7, 6.5 and 7.5(control) mg/L.
Breeding attempts ceased altogether at 4.5 mg/l and lower. At higher concentrations, the effects of DO on reproductive output were contradictory between experiments. When DO was maintained at 5.5 mg/L in the first experiment, egg production was lower than in the controls. When DO levels of 5.7 mg/L were used in the second experiment, egg production was higher than in the controls. Courtship behaviour decreased significantly compared to the control at DO levels of 4.5 mg/L and lower. No significant differences were observed between treatments in morphometrics, survival, larval deformities, sex steroid levels, vitellogenin levels, hatching success, egg size, fertility, or gonad histology.
The results of this study demonstrate that reproductive behaviour may represent a sensitive early marker of reproductive impairment in fathead minnows. Inconsistencies between the two experiments suggest a possible hormetic effect in response to depressed DO in fathead minnows. My results have important implications with respect to Canadian water quality guidelines and applications in the restoration of aquatic systems with lowered DO due to human activities.||en_US