Fish join mosquito war

Montana limits use to isolated pockets of standing water

Matt Gouras, Associated Press

Wednesday, June 28, 2006

BOULDER, Mont. - In an out-of- the-way hot-springs pond just outside of this Montana town, a century-old colony of tropical fish known for their appetite for mosquitoes is giving health officials another way to combat the pesky carriers of West Nile virus.

Ken Staigmiller, a state fish specialist, looks into the pond at the end of a muddy road, reaches in with a net and scoops out hundreds of the hungry 1- to 2-inch fish. Each can eat at least 100 mosquito larvae each day.

"The nice thing about these is, you put them in once at the start of the season, you don't have to worry about them," said Staigmiller, who works with the Montana Department of Fish, Wildlife and Parks.

Thousands are put into water- filled coolers to be transported across the state to mosquito problem areas, but only in places where the aggressive little fish won't harm native fish. The FWP is involved to make sure that doesn't happen.

The mosquito fish, when carefully controlled, are perfect for the job, state officials said.

Chemicals that kill mosquitoes generally have to be applied many times throughout the mosquito season, he said. The fish do it all by themselves.

They are very rapid breeders. A single female can give birth up to 300 young several times a year. Just a single pair of the fish can produce 4,000 descendants during a single summer, according to the state Department of Public Health and Human Services.

Montana wouldn't have any of the fish if it weren't for the hot-spring- fed pond outside of Boulder. The fish were put there in the early 1900s, along with a number of other places, to help deal with mosquitoes.

The fish died off elsewhere. But the year-round warm water of the pond turned out to be a haven for Gambusia affinis.

Regulations barring the importation of non-native fish would likely prevent health officials from bringing the fish into the state today, said Staigmiller. Fortunately the pond produces hundreds of thousands of the fish each year.

But their use is strictly controlled. Wildlife officials want to be certain they are not introduced into the Montana ecosystem in a way that would harm native fish. Some states, such as Wyoming, won't allow the fish to be used.

Montana State University researcher Greg Johnson said he is working on a project to find a native fish that can be used in Wyoming coal-bed methane ponds as effectively as the mosquito fish.

In Montana, Johnson helps monitor the state for outbreaks of West Nile virus for the Centers for Disease Control and Prevention and the state health department. The mosquito fish is a small part of reducing mosquito populations, he said.

"They do have the potential of reducing the mosquito population, especially the nuisance mosquitoes," Johnson said.

The mosquito fish are given only to local mosquito control districts that have outlined exactly how they will be used. They must be used only in isolated pockets of water, like standing water in fields or stock ponds, that are not connected to streams, rivers or lakes.

The fish can't do it all by themselves. Mosquito control districts still have to use chemicals in some areas, and educate residents about minimizing standing water in such places as old tires.

"This is a nice addition to our program," said Dave Klein, the program manager for the Lolo Mosquito Abatement Program.

He recently loaded up buckets with 3,500 to 4,000 of the mosquito fish for use in ponds in low-lying pastures. Hundreds of thousands of the little fish darted about in the pools, where they thrive off a constant supply of warm water from natural hot springs.

Paige Johnson, the West Nile program director for the state health department, said the fish are distributed in fewer than a dozen Montana counties.

"We get positive feedback," she said. "It is one control that can be used to help." But as good as they are at eating mosquitoes, they also have also been known to devastate native species.

The fish is native to the warmer climates of the southern U.S. and northern Mexico. It has been introduced across the country and around the world to control mosquitoes. But because of problems it has caused in warmer climes, biologists have ranked the fish among 100 of the "world's worst invaders." Under the Montana program, the fish must be put in places where they are likely to be killed off by winter. The Department of Fish, Wildlife and Parks makes sure the fish are used only in areas where, even if they survived winter, they couldn't spread into blue-ribbon trout streams.

"We're really into native fish these days," Staigmiller said. "We really don't want to learn the hard way what the negative impacts will be."