Seasonal reproductive patterns of female Gambusia holbrooki from two Florida lakes

Lake Apopka in central Florida (USA) is significantly contaminated with a variety of chemicals including anthropogenic nutrients, organochlorine pesticides like dichlorodiphenyltrichloroethane (DDT) and dichlorodiphenyldichloroethylene (DDE), and multiple congeners of polychlorinated biphenyls (PCBs). Our laboratory has previously documented a number of reproductive abnormalities in alligators from Lake Apopka, compared with alligators captured from Lake Woodruff, a nearby reference lake. We conducted the present study to investigate if another native vertebrate, Gambusia holbrooki (eastern mosquitofish), is similarly affected. Adult female mosquitofish were collected from Lake Apopka and Lake Woodruff monthly for 16 months to document seasonal and lake-associated variation in reproductive patterns. In contrast to fish from Lake Woodruff (reference), females from Lake Apopka exhibited earlier and more synchronized spring ovarian recrudescence, increased body size, increased fecundity, increased adjusted hepatic weight, and more extreme fluctuations in muscle estradiol concentrations in most months. Endocrine disruption, consistent with other studies and Lake Apopka's pollution profile, is one explanation for these findings. Other environmental and physiological factors are also addressed. However, the higher fecundity among Apopka females suggests that, unlike Apopka alligators, Apopka mosquitofish are not impacted at the population level.