Mosquitofish: The Little Fish That Can

This summer, residents of Dallas County have seen a record number of cases of West Nile virus, a serious and sometimes fatal disease spread by mosquitoes. The County has tried to slow the spread of mosquitoes by fogging neighborhoods with insecticide and even spraying from airplanes crisscrossing the affected areas.  Who would have thought that a small, dull-grey fish saddled with a genus name Gambusia (derived from the Cuban Spanish for “useless”) would play an important role in controlling West Nile?

Here at the Demonstration Garden, our small pond is stocked with these one to three inch fish (and one gold fish!) that are enthusiastically contributing to “natural” mosquito control.

Gambusia affinis  is more commonly known as mosquitofish because of its affinity for consuming large amounts of mosquito larvae.  It is estimated that adult females can consume 100 mosquito larvae a day and can eat more than their body weight a day (and they don’t even get fat!!)  Young are born alive and a female can give birth to about 60 babies, several times a year.  Mosquitofish can live in relatively inhospitable environments such as those with low oxygen concentrations and high temperatures.  This means that they can live in small, un-aerated ponds and, importantly in the war on West Nile, stagnant, unused swimming pools.  Many cities, starting in 2008 in California and now in Dallas, are using mosquitofish as mosquito control in stagnant ponds and ditches.

As with anything, one can get too much of a good thing.  Native fish in a stock pond or lake, and even goldfish and koi in an ornamental pond, already eat mosquito larvae.  The introduction of mosquitofish outside their natural range has proved damaging to smaller native fish because of the mosquitofish’s aggressive nature and competition for food   Still, the little fish, that in Russia helped eradicate malaria and has a monument dedicated to it, is one of several weapons for West Nile control in Dallas.  Who knows…. this little fish might save your life.

Carolyn