Salinity holds back mosquitofish invasiveness

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A new study has shown that the invasive success of mosquitofish Gambusia holbrooki can be limited by the salinity of the water.

Carles Alcaraz, Angelo Bisazza and Emili Garcia-Berthou at the Institute of Aquatic Ecology in Spain undertook studies using the mosquitofish and an endangered Mediterranean cyprinodont Aphanius fasciatus.

They compared levels of aggressive behaviour and food competition between the two different species at three different salinity levels.

It was found that as the salinity increased, the mosquitofish decreased their aggressive behaviour towards the cyprinodonts and captured less prey.

In comparison, the cyprinodonts increased defensive acts at higher salinities and caught relatively more prey due to the decreased efficiency of the mosquitofish.

Mosquitofish are related to tropical guppies and are amongst the most invasive fish worldwide; having been introduced to freshwater environments in both tropical and temperate regions as biocontrol for the native mosquitoes.

In the majority of cases, it has since been proven that the endemic fish species were already providing maximum mosquito control.

The introduction of a fish species that could out-compete them as it is more hardy, breeds rapidly (individual populations have been recorded as increasing from 7,000 to 120,000 individuals in just five months), can survive low oxygen levels, high salinities (up to twice the level of seawater) and temperatures of up to 42C has proven devastating to many native species.

In Australia for example, G. holbrooki is considered responsible for the extinction of the rainbowfish in streams around Brisbane.

This study demonstrates that salinity can mediate behaviour and illustrates the importance of considering abiotic as well as biotic conditions when dealing with the treatment of this species.

For more information see Carles Alcaraz, Angelo Bisazza and Emili Garca-Berthou (2007) - Salinity mediates the competitive interactions between invasive mosquitofish and an endangered fish. Oecologica. 2007 Nov 13.