Morphological and reproductive characteristics of male mosquitofish (Gambusia affinis holbrooki) inhabiting sewage-contaminated waters in New South Wales, Australia

The potential effects of exposure of fish to reproductive endocrine disrupt ers (REDs) is of major concern. This study reports on the effects of sewage effluent exposure on morphology of male mosquitofish (Gambusia a. holbrook i) in a tributary of the Hawksbury-Nepean River system in New South Wales, Australia. The growth and development of the modified anal, fin (the gonopo dium, GP) is a secondary sexual characteristic in males, forms under the in fluence of testosterone, and is critical for sperm transfer. The GP was red uced in length in males sampled downstream from a sewage treatment plant di scharge point compared to GP fin length in males upstream or from other com parison sites. The reduction in size of this androgen-dependent structure s uggests the presence of RED substances in the water. The presence or absenc e of spermatozeugmata (sperm packet) was not related to a reduction in GP l ength, which suggests spermatogenesis may not be reduced, but other measure s of fertility remain to be evaluated. These results are discussed in the c ontext of RED contaminants associated with sewage effluent.