Mosquitofish Help Take the Bite Out of Summertime

Jack Hazelrigg dipped a white net into algae-green water and lifted about a dozen silvery, squirming minnows from the shallow pond in front of the Southeast Mosquito Abatement District headquarters in South Gate.

The black-eyed minnows, which look like 1- to 2-inch guppies, are “opportunistic fish,” Hazelrigg said. “They eat everything.”

But one of the things that the fish are best equipped to eat is mosquito larvae--up to 168 larvae in eight hours. And it is because of that special ability that the abatement district expects to distribute about 100,000 of the minnows this year, planting them in lakes and swamps and giving them to people pestered by mosquitoes.

“The thing that makes the fish effective mosquito eaters is that they’re top-feeding minnows,” said Hazelrigg, the district’s assistant manager and entomologist. “The fish go along, skimming the surface and taking in whatever’s there.”

Movable Feast

The mosquito larvae, in comma-shaped “egg rafts” containing 100 to 400 individual eggs, wriggle on the water’s surface, making them prime targets for mosquitofish, which prefer live food, Hazelrigg said.

“We feed them mostly oatmeal here,” he said, though he added that the fish would rather have a commercial fish food.

Mosquito abatement workers routinely collect fresh supplies of mosquitofish from standing water, such as lakes and golf course ponds, and take the minnows back to the pond at the district office. Residents are given mosquitofish according to the amount of standing water to be controlled, usually about two or three dozen fish per 100 square feet of water surface.

Cheaper by the Dozen

After several years of buying mosquitofish at pet stores at three for $1, Gloria Amos heard about the free fish from the abatement district. Earlier this year, the Paramount resident got about a dozen of the minnows to protect her back-yard pond.

“We haven’t had any mosquitoes,” Amos said. “I am assuming that the fish are doing the job.”

Free mosquitofish are also available through three other county mosquito abatement districts: Compton Creek in Compton, Los Angeles County West in Culver City and Antelope Valley in Lancaster.

Hazelrigg wants to change the “very low profile” of the 1,000-square-mile Southeast district--the largest in Los Angeles County--in hopes of increasing the effectiveness of the mosquito-control program. Chemicals are able to eradicate only about 70% of the area’s mosquitoes, and Hazelrigg said residents could handle the rest of the problem.

Hazelrigg suspects that most people don’t know that any container of standing water, from an abandoned pool to an ornamental pond to a saucer under a potted plant, is likely to breed mosquitoes in seven to 10 days.

“A large amount of mosquito control is (the residents’) responsibility,” he said.

And one of the easiest ways to deal with mosquitoes is by using mosquitofish.

One of the nation’s oldest forms of biological control, mosquitofish-- Gambusia affinis-- were used as early as 1901 to control the malaria-carrying insects in the South. The California mosquitofish population originated in 1922 when the state Board of Health shipped 590 minnows from Austin, Tex., to a lily pond in Sacramento.

The state then set up 25 hatcheries throughout the state to breed and distribute the fish, and in the last 56 years the species has become entrenched in California, Hazelrigg said. Although other fish, such as guppies, goldfish and carp, also eat mosquito larvae, none are as efficient as the mosquitofish, which is used by all of the state’s 60 mosquito abatement districts, he said.

Mosquitofish are valued for their tolerance to most types of pesticides, their ability to bear live young and their varied diet. The fish have been known to eat more than 50 types of plant and animal life, including their own newborn, according to research studies.

Mosquitoes are kept in check mostly through the use of two kinds of insecticides, an oil that prevents larvae from breathing air on the water’s surface, and a growth-regulating chemical that keeps the larvae from making new skin while growing.

Insecticides make up 90% of the control effort in the Southeast district, which covers 32 cities from the San Fernando Valley through Los Angeles and south to San Pedro.

Mosquitoes are more than a nuisance. Some carry diseases, including malaria and the dangerous St. Louis encephalitis, a viral disease that can cause inflammation of the brain and spinal cord.

Disease-carrying mosquitoes have shown up several months earlier than usual this year.

California is now in the height of its mosquito season, which lasts from May to October. Despite the unexpected early detection of encephalitis in Long Beach and Santa Fe Springs, “We’re having an average year,” Hazelrigg said.