Reproductive morphology of male mosquitofish (gambusia holbrooki) inhabiting sewage-contaminated waters in the South Creek catchment on the Hawkesbury-Nepean River

Abstract

It has recently become apparent that effluent from sewage treatment plants (STPs) may contain substances that are oestrogenic to fish. In this study, we assessed the reproductive morphology of male eastern mosquitofish (Gambusia holbrooki) inhabiting sewage contaminated waters in the South Creek catchment of the Hawkesbury-Nepean River. Male mosquitofish were collected downstream of two STPs, located at St Marys and Quakers Hill. Fish were also collected from upstream of each STP for comparative purposes. The gonopodium, a modified anal fin that is used to transfer sperm during copulation, was found to be reduced in length in male mosquitofish collected downstream of St Marys STP compared to fish from upstream of the effluent outfall. The testicular weight of the downstream males was also lower than that of the upstream fish. Exposure of male mosquitofish to oestrogenic chemicals under laboratory condition has previously been demonstrated to affect gonopodium length and testicular development. There were no differences in the reproductive morphology of male mosquitofish downstream of Quakers Hill STP compared to the upstream fish. Future surveys of mosquitofish populations inhabiting sewage -contaminated waters in the Sydney region should include more direct evidence of oestrogenic exposure, such as vitellogenin induction and gonadal histology.