Gambusia in New Zealand: Really bad or just misunderstood?

Abstract

Mosquitofish (Gambusia spp.) have been spread throughout most of the temperate world during the 20th Century as biological control agents for mosquitoes. However, in many areas of introduction these small aggressive fish have been implicated in the displacement or exclusion of native species of fish and amphibians. Those species most affected are small, surface-feeding, littoral-zone fishes and the egg and larval stages of amphibians. In New Zealand, the western mosquitofish, Gambusia affinis, was introduced at Auckland in 1930 and has since spread throughout much of the North Island with recent introductions to the northern South Island. They have been implicated in the decline of dwarf inanga, Galaxias gracilis, and may affect recruitment of black mudfish, although the continued abundance of inanga, mudfish, and other small-bodied natives at sites long inhabited by Gambusia implies that competition or predation by the latter may be minimal and that Gambusia occupies an underutilised niche in New Zealand aquatic environments. The ability of Gambusia to cause ecosystem alteration by selective removal of invertebrate grazers is possibly of greater concern in New Zealand than any perceived threat to native fishes. © 2004, Copyright Taylor & Francis Group, LLC.