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Mosquito Fish Another Tool For Disease Prevention

On a hot, sunny Saturday morning at the Upper Tampa Bay Regional Public Library, Kathy and Dani Dahlberg walk up to a white truck holding portable fish tanks that emit a loud hum.

The new homeowners are trying to describe the size of their pond to Hillsborough County Mosquito Control officials.

"Ok, so it goes from…” Kathy Dalhberg said.

“One acre? Two acres?” asks John Waleri.

“Yeah, it’s about an acre,” Kathy Dahlberg replies. “We have four acres and an acre of pond.”

“It's likely you already have these in your pond,” Waleri said.

County officials this summer are giving away "mosquito fish,” a guppy-like, native freshwater fish - for free - to residents.

The two-and-a-half-inch long fish can eat about 100 mosquito eggs and larvae a day. They flourish in backyard ponds, birdbaths, fountains, animal troughs, unused swimming pools and other standing water.

They require no feeding, and care is limited to protecting them from garden sprays, chlorine, or other chemicals used for cleaning. Mosquito fish do not lay eggs and need no special environment for breeding.

As they do every hurricane season, mosquito control officials across the state have amped up their efforts to fight the disease-spreading pests. This includes spraying Naled, a pesticide widely used to fight Zika-carrying mosquitoes in Florida and across the nation.

It riled up Miami Beach last year when protesters interrupted a city council meeting to challenge its use. The city council then urged Miami-Dade County to pursue alternatives.

More recently, a University of Michigan study shows a possible link between Naled and motor function issues in babies.

While mosquito control officials say the spray is safe in small amounts, they also say it's more efficient to focus on preventing mosquitos from laying and hatching eggs than to fight the bugs in their flying form.

Hillsborough County Mosquito Control Operations Manager Ron Montgomery said prevention is key, but it's not always easy.

"The rainfall and the heat are directly related to mosquito production,” Montgomery said. “The hotter it is and the more nutritional substance that is in the habitat for the mosquito to eat, the faster they develop, and they go from an egg to an adult mosquito sometimes in three or four days, which makes that challenge to treat that larval habitat even that much more difficult."

That's where mosquito fish come in.

Kathy Dahlberg said when they bought their property in Odessa earlier this year, Southwest Florida Water Management District - known as "Swiftmud" - told them mosquito control was top priority.

"After we bought the house, we did all the kind of research you do about how you take care of it. We called Swiftmud to say, "What else do we need to do?’ And this was among the first things, to make sure we take care of mosquitoes,” Kathy Dahlberg said.

The women walk away with state fair-style plastic baggie of mosquito fish. Most of them have swollen, translucent bellies and will soon give birth to live babies.

So far this year, more than 70 people in Florida have tested positive for Zika. Most of the cases are travel-related, and most people who contract it don't show symptoms.

But pregnant women - including almost 50 diagnosed with Zika in Florida this year - are at serious risk because the virus has been linked to microcephaly in babies.

Zika isn’t the only concern to public health officials.

Vilma Vega, an infectious diseases specialist in Sarasota, said she's just as concerned about other diseases, like a recent outbreak of yellow fever in Brazil.

"It's not going to take much for such a disease to get transferred into any other country,” Vega said. “We definitely need to keep our eyes open."

For now, Zika is what people are talking about, and that's fine for Ron Montgomery because the fish that help prevent Zika also help prevent other diseases.

Back at the Hillsborough County Mosquito Control Office, Montgomery said Floridians who don't live in his county can still easily get the mosquito larva-munching fish.

"If you're not part of a mosquito control program that has them, which I would encourage you to check first, you can get them at pet stores,” Montgomery said. “You can buy them mail order and have them shipped to you overnight.”

In the meantime, Montgomery rattles off some tried-and-true mosquito prevention methods we all know: empty containers of standing water, recycle old tires, cover exposed skin with clothing and use bug spray.

The county also  has a new high-tech weapon to confront the menace: a computer mapping system that shows the entire county in real-time detail. The Mosquito Analytics and Response System "greatly enhances the agency's ability to identify and manage areas frequented by the insects," according to the county's website. 

"In its first month of use, Mosquito Control plotted more than 1,800 larvae production sites. The computerized map, displayed on two oversized monitors at Mosquito Control's headquarters on Eureka Springs Road, replaces antiquated wall maps and push pins. Field inspectors stay in synch with their supervisors at the command center by carrying tablets that let them monitor problem areas in their assigned regions throughout the county."

Click here for a list of mosquito fish giveaway events in Hillsborough County.

Leon County Judge John Cooper on June 30, 2022, in a screen grab from The Florida Channel.
Credit Common Backyard Mosquito Sources image as courtesy of the Marin/Sonoma Mosquito & Vector Control District.
The Florida Channel
Leon County Judge John Cooper on June 30, 2022, in a screen grab from The Florida Channel.

Daylina Miller is a multimedia reporter for WUSF and Health News Florida, covering health in the Tampa Bay area and across the state.