Anal fin morphology and gonadal histopathology in mosquitofish (Gambusia holbrooki) exposed to treated municipal sewage effluent.

Feral mosquitofish living in undiluted treated municipal sewage in Queensland, Australia, were examined for morphologic abnormalities indicative of reproductive dysfunction. Male and female mosquitofish were captured at two sites receiving undiluted treated sewage and compared with those captured at a reference site. Several morphologic end points were examined, including length of the fourth and sixth anal fin rays and gonadal histology. Both male and female mosquitofish at one site exhibited minor elongation of the fourth anal fin ray consistent with exposure to androgenic stimulation, although the spatial extent of the effect was limited and not significant at other sites further downstream. No incidences of intersex were found. These findings suggest that the level of treatment of domestic sewage at the two sewage treatment plants assessed is adequate to prevent reproductive abnormalities in exposed mosquitofish populations.