Reproductive Success of Eastern Mosquitofish (Gambusia affinis) Exposed to Pulp and Paper Dominated Receiving Streams and Effects of Masculinization Responses

Abstract

Mosquitofish (Gambusia) are sexually dimorphic; adult males have an elongation of the anal fin to form a copulatory structure known as a gonopodium. Several studies since the early 1980s have reported elongated anal fins in female mosquitofish exposed to pulp and paper mill discharge, a phenomenon known as masculinization. Although adverse impacts have been suggested in these previous reports, the influence of masculinization on reproductive success has not been assessed for pulp mill effluent-exposed eastern mosquitofish (Gambusia holbrooki or affinis). The current study compared fecundity (number of fry per female at parturition) to an index of masculinization (ratio of anal fin rays 4 to 6). Pregnant females were collected from two effluent-receiving streams in Florida: Rice Creek and the Fenholloway River, over two reproductive seasons (2003 and 2004). Masculinization was consistent between years, with clear effects at the Fenholloway River site, while the response was minimal or nondetectable at the Rice Creek site. Masculinization was not correlated with the production of fry/fecundity at either site. Data suggest differing reproductive seasonal strategies between basins and populations but do not demonstrate any effects of pulp and paper exposure on reproductive success in mosquitofish.