A Healthy Appetite : Mosquitofish Feasts on Its Namesake

John Parsons visits several back-yard swimming pools a week.

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If the pools are clean, he congratulates their owners, chit-chats a bit about mosquitoes and goes his merry way. If they are dirty, however, watch out. Parsons dumps bucketfuls of tiny fish in the water that will thrive, multiply and dominate the pool within days.

“We try to work with people,” says Parsons, a technician with the county’s pest control agency who has the legal authority to dump fish in a pool with or without the owner’s consent, at no cost to the owner. “Most are cooperative because they realize it’s for their own benefit.”

Meet Gambusia affinis , Orange County’s fish with a purpose. Its mission: to rid the county of its burgeoning population of mosquito larvae, those irksome little insects which, as adults, spread disease and make summer barbecues hell.

“These guys are wonderful,” Parsons says of the critters whose eating habits, county officials estimate, save taxpayers $300,000 a year. “They just love eating mosquito larvae. They have ravenous appetites and never seem full.”

Gil Challet, the district’s manager, couldn’t agree more. “I like them,” he says. “It’s a perfect example of biological control.”

Commonly known as mosquitofish, the tiny members of the guppy family--native to the Southeastern United States--have been eating floating mosquito larvae in California since the early 1920s when they were imported for that purpose. Today in Orange County, Challet said, about 100,000 of them are planted each year in various bodies of water, including flood control channels, storm drains, ponds and streams. Of that number, he said, about 25%--or 25,000--end up in private swimming pools, whether the owners like it or not.

“We give them a choice,” the Vector Control District manager said of the roughly 1,000 pool owners who end up on the county’s list of potential mosquitofish recipients each year. “They can either clean up their pool or we’ll put mosquitofish in it.”

Homeowners end up on that list in a number of ways, according to Challet. Ordinarily when swimming pools are regularly used and their filtration systems kept running, he said, mosquitoes are not a problem. If a pool is left abandoned or uncleaned for even a short period, however, it can become a breeding ground for egg-laying malaria and encephalitis-spreading mosquitoes, a situation that usually prompts disturbed neighbors or city health workers to contact county officials.

Reported pool owners are given a week to clean up their acts. If they don’t comply, Challet said, vector control technicians bearing buckets enter the property and dump as many as 50 mosquitofish into the pool, where they usually thrive and multiply indefinitely, or until the owner decides to add chlorine and turn on the filter.

“They’re perfect,” Challet says of the silvery little fish, which are raised in 12 ponds built for the purpose at Vector Control District headquarters in Garden Grove. “Without them we would probably have to double our pesticide use” and significantly increase the crew.

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Not everyone reacts positively to the idea of sharing their would-be swimming space with dozens of squirming, mosquito-eating critters.

Once, Parsons said, the hostile principal of a church-run school whose pool had made the county’s list met him at the gate with one hand behind his back. “I didn’t know whether he had a gun or not,” Parsons said, “so I decided to retreat.”

Later negotiations melted the resistance, Parsons said, and in most instances people cooperate fully, often preferring the help of nature to the expense and effort of restoring their pools. The fish can stay for as long as 15 to 20 years.

That wasn’t the plan of Danny Benavente, a Buena Park resident whose pool was the subject of a report to county officials last week. Arriving at the house, Parsons found the pool owner busily refilling his drained back-yard swimming hole with fresh water while preparing to treat it with chemicals.

“It was unavoidable,” Benavente said, explaining that the pool had not been maintained for a time after the recent death of a family member. “I neglected to clean it.”

After a brief inspection, Parsons declared the facility unworthy of biological intervention. “The remnants of the larvae are there,” he said, “but they are about to die anyway,” making the mosquitofish unnecessary.

Not so in the case of Patrick Dwyer, a retired aerospace worker living in Fountain Valley.

Until five years ago, Dwyer’s pool was in good working order. Then a drain got clogged, messing up the filter system and necessitating costly repairs. Instead of making payments he couldn’t afford, the owner--who is in a wheelchair--opted to drain the pool and “just shut it down,” he said.

Then the rains came, half refilling the empty pool and creating a mosquito-larvae haven. Dwyer called the county Vector Control District to request a colony of mosquitofish.

“They really do the job,” he says of the hundreds of fish now occupying what used to be his pool. “I love watching them.”

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A Mosquito’s Worst Enemy

Chlorine and other pool-cleaning chemicals will not kill mosquito larvae, but a hungry little fish is jumping into Orange County pools to take the bite out of mosquito populations. Details on mosquito fish:

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Mosquitofish

* Size: One-fourth inch at birth; reaches full size of 3 inches in six to eight weeks

* Diet: Mosquito larvae

* Breeding season: Summer; produces 50 to 100 young every six weeks

* Care: Must be protected from garden sprays, chlorine and other chemicals used to clean ponds or pools

* Availability: Free; call Orange County Vector Control District, (714) 971-2421

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Other Control Methods To prevent a mosquito infestation, pools and spas should be cleaned daily and pond vegetation should be thinned out regularly. Other tips:

* Ornamental ponds: If unused, break hole into bottom, drain, then fill with dirt or sand * Pools and spas: Provide drainage for filter and pumps; remove any water from cover

* Open boats: Drain bilge water; if unused, store upside down or cover with tarp

* Animal water troughs: Clean weekly

* Containers: Store upside down; properly dispose of all unusable containers

Source: Orange County Vector Control District; Researched by JANICE L. JONES/Los Angeles Times