Use of Mosquito Fish to control Zika vectors


Mosquito fish, Gambusia affinis, are small live-bearing fish occurring naturally in permanent streams and lakes throughout eastern and southeastern United States. Decades ago, when malaria was prevalent, the U.S. Soil Conservation Service provided assistance to landowners desiring to construct farm ponds on their property, and required introduction of Gambusia into the pond when it began to fill. This was primarily to prevent the breeding of the malaria vector, the mosquito, Anopheles quadrimaculatus.
Malaria has been essentially eradicated from the U.S. The mosquito borne disease, Zika, is now causing problems. It is transmitted by the mosquitoes Aedes aegypti and A. albopictus.. It is endemic throughout much of Mexico, South and Central America, the Caribbean, Southeastern Asia, and many African countries. It is also transmitted from person to person through sexual intercourse. Of 193 confirmed cases of Zika in the U.S., all have been directly or indirectly related to persons traveling to endemic areas. Three cases are known from Alabama and as many as nine more are suspected as having contracted the disease. Individuals having Zika may have only moderate symptoms. The most severely affected are babies born to infected mothers. The babies are likely to suffer from microcephaly, characterized by abnormally small heads and brains and associated neurological disorders.
Women are strongly advised to avoid traveling to endemic countries and avoid getting pregnant for an extended period of time afterward. They are also advised to use contraceptive measures when engaging in sex with men who have visited the countries. Authorities in some countries where Zika is endemic are advised to use whatever means possible to avoid getting pregnant. If that advice is followed, the worldwide birth rate is destined to decline, perhaps dramatically.
Optimal breeding sites for Aedes mosquitoes are stagnant fishless pools that fill depressions with water following periods of rainy weather. Such pools may persist for weeks or even a month or more, and provide the sources of thousands of mosquitoes. In a recent column I mentioned placing “mosquito dunks” in such places. They kill mosquito larvae and pupae of mosquitoes, midges, and other obnoxious pests, but are harmless to other animals. I failed to mention introducing Gambusia into these sites. Some places in California are using them for mosquito control as is at least one county in New Jersey. Releasing Gambusia in farm ponds where they do not occur naturally or into ephemeral rainwater pools should cause few if any problems, although some ichthyologists disagree. They contend that Gambusia feed on eggs and fry of desirable fish and feed on some macroinvertebrates.
There is, however, documented evidence that they do harm two frog species in Australia, where they were released in an effort to control mosquitoes.
I am aware of no evidence that releasing Gambusia in ephemeral rainwater pools cause any harm to any species, except for mosquitoes and midges. Southeastern Pond Management does not supply Gambusia, but they are easily caught in baited minnow traps. The traps are available locally at Walmart and possibly other outlets.
County authorities responsible for mosquito control may wish to consider using Gambusia.
Bob Mount is a Professor Emeritus with the Department of Zoology and Entomology at Auburn University. He is also chairman of the Opelika Order of Geezers, well-known local think tank and political clearing house. He writes about birds, snakes, turtles, bugs and assorted conservation topics.


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