Fishing for a way to control mosquitoes

Fulstone Wetlands is a place in Carson City where mosquitoes thrive during the summer. And Teresa Hayes is trying something different to make the area less hospitable to the insects, which carry life-threatening diseases.

The environmental health specialist with city Health and Human Services learned about how Gambusia Affinis, better known as mosquito fish, can help control infestations by dining on the larvae, while attending college and has been following the research ever since, she said.

"I'm waiting to see whether putting the fish in different areas can control the mosquitoes for me," Hayes said. "And the fish work for free."

Last summer she grabbed two buckets, a net and drove out to Eagle Valley Creek behind St. Teresa Catholic Community on Lompa Lane, part of a wetlands system that extends across 45 acres northeast of the city's center.

She fished out 50 fish and put them in the buckets. The fish are no longer than a Tootsie Roll and resemble guppies.

"I tried to get fish from different generations, and enough gene bases to multiply," she said. "Winters for them can be tough, so I wanted to give them time to acclimate."

She transplanted the fish to a creek within Fulstone because it's considered one of the areas around the city with heaviest mosquito infestation. The Fulstone Wetlands are east of the Northridge subdivision, north of Northridge Drive and west of the Carson City freeway.

Hayes repeated the process and took some more of the fish to the water retention basin next to Western Nevada Community College. Mosquitoes also thrive in its shallow sections, she said.

Though there have been days with unseasonably high temperatures this winter, it still hasn't been warm enough for the little fish to come out yet.

Hayes tries to visit the sites where she transplanted the fish once a month and keeps a log detailing conditions. It's not an official experiment, it's just a potential way to control the mosquitoes without using chemicals, which are applied "only as a last resort," she said.

Methoprene is used to control mosquitoes because it's a growth inhibitor that affects larvae. Those offspring aren't able to reproduce because they remain physically juvenile or malformed, so they can't bear offspring but still are part of the food chain.

Mosquito fish "are a really good tool for managing mosquitoes," said Kim Tisdale, the Nevada Division of Wildlife's western region supervising fisheries biologist. "The effect on native species is minimum and they control mosquitoes without pesticides - that's a good thing."

The little fish are a favorite food of bass, brown trout and birds. Bats also like to eat mosquito larvae, Tisdale said.

State officials have just started mosquito monitoring this year, though horses have been watched year round. If the weather trend continues, this year's mosquito season could end up being characterized as "average."

"We haven't had a lot of precipitation this year," said Dr. Anette Rink, director of the animal, disease and food safety laboratory for the state of Nevada. "We're 40 percent behind the 10-year average but there have been two heavy winters before. Not all that water will dry up."

Less standing water means fewer breeding grounds than in the past couple of years, though "a lot of natural wetlands only dry during an extended period of drought," she said.

West Nile virus, St. Louis encephalitis and Western Equine encephalitis are the major diseases mosquitoes carry in this region. While some mosquitoes focus on feeding on the blood of birds, the type here are dangerous because they're "indiscriminate," Rink said.

"Here they'll nosh on a bird, have dinner on a horse, then move on to the horse's owner," she said.

Time will tell whether the fish took to their new surroundings, Hayes said. She expects the fish to be visible - and feeding on larvae - within the next couple of months.

"There are other ways to do things, good ways to handle them other than destroying the environment," she said.

Residents interested in information about obtaining mosquito fish can call Hayes at 887-2190. People going out to areas and removing the fish themselves can damage the surrounding habitat and endanger other animals and plants, she emphasized.

And people aren't supposed to move fish from one place to another without a state permit, according to the Nevada Division of Wildlife.

• Contact reporter Terri Harber at tharber @nevadaappeal.com or 882-2111, ext. 215.