Western mosquitofish (Gambusia affinis) bolster the prevalence and severity of tadpole tail injuries in experimental wetlands

Species introduced outside their native range to serve anthropogenic purposes may have unintended consequences on native organisms. Mosquitofish (Gambusia affinis and Gambusia holbrooki) have been introduced throughout the world to control larval mosquito populations in aquatic environments, but they have also been implicated in the decline of native fish, amphibian, and aquatic invertebrate populations. We investigated the roles of introduced western mosquitofish (G. affinis), and two naturally colonizing predators (crayfish and dragonfly naiads) in inflicting tail injuries observed on ranid frog tadpoles in experimental constructed wetlands. We also examined the influence of vegetation in reducing tail injury severity. We found that mosquitofish significantly increased the prevalence and severity of tail injuries, but crayfish and dragonfly naiads contributed much less to increased injury levels. Furthermore, increased vegetation cover did not significantly attenuate tail injuries. However, after chemical removal of Gambusia, injury prevalence and severity was significantly reduced. Although previous investigations have concluded that mosquitofish prey upon the eggs and larvae of some amphibians, our results illustrate that these fish can cause substantial but apparently sub-lethal injuries to large numbers of larval amphibians in a wetland. Further investigations are needed to determine if these injuries impede the fitness of victims and lead to population reductions.