Impact of the introduced poeciliid Gambusia holbrooki (Girard, 1859) on the growth and reproduction of Pseudomugil signifer (Kner, 1865) in Australia

The impact of the presence of the introduced poeciliid Gambusia holbrooki on the Australian pseudomugilid Pseudomugil signifer was examined in open-air tank experiments. G. holbrooki profoundly affected the breeding of P. signifer . In the presence of G. holbrooki , P. signifer did not gain weight or grow in total length, ovarian weight and fecundity were greatly reduced, and the ovaries were morphologically undeveloped. No eggs of P. signifer were observed in tanks that also housed G. holbrooki . The results indicate that, at least in a captive situation, the presence of the exotic species had a very deleterious effect on the breeding and hence possible survival of the native species. These results are discussed with reference to the conservation of Australian pseudomugilid species, especially those inhabiting confined habitats.