APPENDIX II-AZ: Gambusia affinis: Fish instead of Spraying


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Tiny fish help stop spread of mosquitoes


Record Staff Writer

April 30, 2007 6:00 AM

A small fish with an insatiable appetite and a knack for producing offspring is fast becoming a popular weapon in San Joaquin County's battle against mosquitoes and West Nile virus, officials said.

The San Joaquin County Mosquito and Vector Control District has offered the aptly named mosquitofish - scientists know them as Gambusia affinis - free of charge for years to prevent the spread of mosquitoes in the spring and summer, district spokesman Aaron Devencenzi said. The fish are placed in unused swimming pools, water troughs, backyard ponds and other isolated water containers where mosquitoes lay eggs.

Mosquitoes breed in standing water, and the silver, minnow-size fish are known to gobble the larvae as they hatch. "They pretty much eat anything they can get ahold of," Devencenzi said.

More residents began asking for the fish after West Nile virus, carried by birds and transmitted to humans and horses by mosquitoes, surfaced in the area three years ago, Devencenzi said. With temperatures expected to reach summerlike highs this weekend, the district is encouraging more people to use the fish to reduce the risk of West Nile's spread this year.

"This is one way we can control mosquitoes without having to spray" insecticide, Devencenzi said.

Michael Perez, a 71-year-old Collegeville resident, plans to put mosquitofish in the backyard pond his daughter recently built to keep the pesky insects off his property. He owns a small ranch on which he raises steer, chickens and sheep, and he wants to make sure both his family and his animals are protected from the virus.

Perez also hopes the fish will save some of the wild birds that often flock to his rural property. Dead birds often are a sign that West Nile is in the area.

"Every year at this time, these swallows will come and build their nest here," Perez said. "Hopefully, that'll protect them."

West Nile activity has fluctuated in San Joaquin County since the virus arrived in 2004. Only three people tested positive that year, but infections spiked to 36 in 2005 and led to the death of an 86-year-old Acampo man before ebbing considerably last year.

Most people who contract the virus show no symptoms. About one in five develops the flulike West Nile fever, which can last weeks to months. A smaller number, about one in 150, develop a more-serious neurological disease.

No trace of the virus has surfaced in the county so far this year.

The county's mosquitofish are raised and stored in 13 ponds near Lodi's White Slough wastewater treatment plant, off Interstate 5, Devencenzi said. One pound of the tiny fish is enough to protect an acre of water, because the fish multiply quickly and never stop eating, he said.

Officials hope increased usage of mosquitofish will lower the number of mosquitoes in the county this year, although they still stress other measures to avoid the virus, such as using insect repellent, wearing long sleeves and long pants, emptying standing water that can be drained and staying indoors at dusk and dawn. Even though West Nile infections fell off noticeably across the county last year, officials aren't ready to deem the virus under control.

"We're always preparing for the worst," Devencenzi said. "We don't have a crystal ball. With this disease, we don't know."

Contact reporter Greg Kane at (209) 546-8276 or

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