Feral Fish

A fishy tale - Gambusia holbrooki

While you might be lucky enough to spot a tortoise or a pied cormorant at your local wetland, chances are Gambusia holbrooki or Mosquito Fish will be present in vast numbers. These small fish - they only grow to 6cm - were introduced from America. Like many stories of introducing species from foreign places, Gambusia breed crazily fast and suffer little predation. They eat native fish, macroinvertebrates and tadpole larvae. Gambusia were introduced because it was thought they did a good job controlling mosquitos.


Research has shown that well designed wetlands without stagnant pockets of water and with good native fauna do a better job for keeping mosquitos in check. If you have a mosquito problem at your place – go round and throw out all the stagnant water that forms in plant saucers and non-circulating water features.

So what can we do about Gambusia?

  1. Ecologist from the Directorate are trialling the use of special nets that can be used to catch these fish. While they won’t capture every individual they’ll help reduce overall numbers.
  2. Never transfer fish from a wetland to another wetland or to a backyard pond. Wetlands and backyard ponds are connected to the urban stormwater system and this is one of the ways Gambusia spread.