Gambusia Damnbusia
by Carmen Welss
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Gambusia Damnbusia |
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| When thinking of pest species the red fox, feral cats, dogs, goats and pigs are the first animals that come to mind. Underwater however, undetected by most of us, there is a predator that poses a devastating threat to the native frogs and fish in our waterways – Gambusia holbrooki or Mosquitofish. The damage done by this exotic fish is so severe that the international Gambusia Control Network would like to see its common name changed from Mosquitofish to “Damnbusia.” A name that seems not only more suitable for the species outside its natural range, but also far more educational and valuable than “mosquitofish”. It received this name because of its reputation as a mosquito eater. In Australian waters, however, it does not seem to be more efficient than any native species.
As part of the Gambusia Threat Abatement Plan the Foundation funded the production of the poster “Freshwater Fishes of the Sydney Region.” It will soon be on display at aquarium shops advising customers who are looking for suitable residents for their aquariums and ponds. Profile of a fin-nipping tadpole eater The poster promotes native, tadpole-friendly fish species for aquarium and pond owners and warns of the dangers of releasing exotic species into our waterways. Gambusia is one of these noxious fish against which the poster takes out a warrant. The Eastern Gambusia is native to the rivers of southeastern USA. It was introduced into Australia in the 1920s as a natural means of controlling mosquitoes. Not only did the experiment fail to achieve the desired outcome. The introduced species is now a widespread major pest in fresh coastal and inland waters of New South Wales, Victoria, and South Australia. In many streams it greatly outnumbers native species. Masters of Adaptation The species is only small with female Gambusias growing to 60mm and the males reaching 35mm. However, it has several competitive advantages over small native fishes and frogs. Gambusia can tolerate a wide range of temperatures (from under ice to 44°C) and water conditions, from freshwater to seawater. Its food range is wide and includes ants, flies, aquatic bugs and beetles. It has a high reproductive rate (an average of 50 young per brood, with up to nine broods per year); it matures quickly and displays aggressive fin-nipping behaviour. When resources are limited gambusia prey on eggs and larvae of endemic fishes and amphibians. In Australia, gambusia was suggested to be an imminent threat to red finned blue eye (Scaturiginichthys vermeilipinnis, Pseudomugilidae) and Edgbaston goby (Chlamydogobius squamigenus, Gobiidae). They also negatively effect southern blue eye (Pseudomugil signifer) populations and tadpoles. What can be done? Complete eradication it seems is impossible to achieve. Various options, including alteration of water flow rate, netting, and application of piscicides have been trialled but are presently outside the scope of this discussion. Scientists are now looking at biological agents, ranging from retroviruses to bacteria, parasites and funguses, in their search hoping for a means to control the pest Gambusia. However, to date there is no weapon against Gambusia that does not bear the risk of harming other native species or their habitat. The best way to protect our native frogs and fish species is therefore to avoid the introduction of non-local fish in the first place. Exotic species can escape from ponds when their water overflows after heavy rain. Placing screened overflows that control where water runs off and stop possible escapees are a simple yet efficient measure. The DEC together with the NSW Australia New Guinea Fishes Association designed the poster which is to be distributed to Sydney aquariums. |
