Construction workers have been at work demolishing an abandoned tuberculosis hospital in Queens over the past several months, dismantling the long-empty wards and carting off the bricks. But first, they had to figure out what to do with a school of goldfish which for unknown reasons had come to call the flooded basement home. Three hundred of them.

Their go-to goldfish rescuer? A beautician from the Bronx.

Brenda Prohaska, who teaches cosmetology at an alternative learning high school, had only a passing interest in fish when she joined a local aquarium interest group a few years ago. She just had some questions about how to treat ich, an illness that had wiped out her mollies. Then the pandemic lockdown began and the fish club became a fish 911.

Messages poured in: There were sultan fish languishing in a closed acupuncture office in Midtown Manhattan, a cluster of spike-topped apple snails forfeited by a Bronx family fleeing the contagion, and a nearly 20-year-old Oscar fish in Co-Op City whose owner had died of the coronavirus.

“I thought someone else would answer the call,” Ms. Prohaska, 51, said in an interview in her house on City Island in the Bronx, over the burble of hundreds of gallons of aquarium water. Beside her, the foot-long sultan fish from the acupuncture office chewed a fresh earthworm she had plopped in his tank. “They didn’t, so I had to.”

Ms. Prohaska has since taken up a heavy mantle few — including herself — knew was there for the taking-up: She has become the city’s on-call fish rescuer. The safe extraction of most of the mysterious goldfish from beneath the Neponsit Adult Home in Rockaway Park was just one of about 90 rescues she has undertaken in the past three years.

(Like any good fish tale, the goldfish caper gets bigger in the retelling: The Rockaway rescue effort included not just nets, traps and crusts of bread but a group of L.G.B.T.Q. activists who frequented the beach nearby, a disabled construction worker from Pennsylvania and a woman who asked to be known as a “fish fairy godmother” for privacy. But more on that later.)

The pandemic has ebbed, but Ms. Prohaska has not stopped. The fish need her too much, she says. The volume may be related to a post-pandemic phenomenon: giving away pets that were purchased as a lockdown balm. Small-animal intakes spiked by more than 12 percent nationwide in 2022, compared with the year before, according to Shelter Animals Count, which collects data from more than 6,000 shelters, though they still remain about 9 percent lower than before the pandemic. Via her Facebook page, NYC Fish Rescue, people alert Ms. Prohaska to their fish problems.

They are as varied as fish in the sea: a messy divorce in which a restraining order prevented a spouse from collecting his fahaka pufferfish; a man moving to California stopped by Transportation Security Administration agents at the airport for trying to take his suckermouth catfish in his carry-on bag.

Though people give Ms. Prohaska fish and their trappings, NYC Fish Rescue is not a business. She plans to create a nonprofit entity but has not yet had time.

Ms. Prohaska has a hard time explaining why the plight of helpless fish called to her. A cancer survivor, she says saving them gave her a sense of control, particularly during the pandemic. “I always have been a giver, so it almost comes easy to me,” she said. “They are living things, and I feel like nobody really cares that much.”

At first she kept every angelfish, betta and gourami. She drove to save them in a beat-up hearse that she bought from a haunted attraction in Connecticut and that now serves as her fish rescue ambulance. (It is filled with fish gravel, aquarium filters and a terrifying clown mannequin from its previous life.) But the stress of cleaning multiple tanks and worrying about the creatures was too taxing, she said. She had to move one tank out of her bedroom because fretting over the cichlid’s happiness left her sleepless.

“It’s taxing — I worry about the fish,” she said. “It’s what drives me; I do it. But I don’t know if it’s good for me because it just causes me heartache and stress.”

Eventually, a man named Laboy Wiggins rescued the fish rescuer. Mr. Wiggins, 51, a disabled construction worker who lives in West Pittston, Pa., found NYC Fish Rescue on Facebook in 2020. The connection between the two fish sympathizers was instant, both said. Now, sometimes several times a week, he loads his Lincoln Navigator with the tools of the fish rescue trade — buckets and nets — and drives upward of three hours to New York City to rescue the fish to which Ms. Prohaska directs him.

Fish grew from a pastime to a solace for Mr. Wiggins, who took up the hobby when a car accident shattered his leg in 2009, requiring more than 30 surgeries, he said. Soon, it became an all-encompassing passion. “I just went berserk,” he said. “I went really crazy with it, but it’s a good kind of crazy. Fish is peaceful.”

He gets peace from the 700-gallon tank he installed in his living room, and the 500-gallon one upstairs, home to two Amazonian pacus that he rescued at Ms. Prohaska’s behest from a Long Island Rail Road depot in Queens. Their owner, a longtime railroad employee who was retiring, had kept them for over a decade, Mr. Wiggins said, but could not take them home. They are huge.

He found that keeping fish was much more than just a way to pass time while immobilized: A child sexual abuse survivor, Mr. Wiggins spent 18 years in prison for robbery and assault and was released about 15 years ago. “I was acting out my trauma,” he said. In 2020 he joined a number of men in suing a Pennsylvania reform school where he says he was abused. The opportunity to rescue fish with Ms. Prohaska felt healing.

“These fish is innocent,” he said. “And they are being mistreated — they didn’t ask for that.”

Mr. Wiggins and Ms. Prohaska find it galling that, while dog and cat rescues abound, there are few dedicated fish rescues, and that the animals, some of which live for decades, are often dumped or even flushed.

Since 2018, Animal Care Centers of New York City, which takes in surrendered animals, has received just 144 fish and one hermit crab, according to Katy Hansen, a spokeswoman. “It’s hard to believe that in a city of nine million we’ve only taken in about 140 fish, when we’ve taken in thousands of other animals,” Ms. Hansen said. “My biggest fear is that people are just flushing them down the toilet, and they are sentient beings.”

In the next few days, Mr. Wiggins will receive a special delivery from New York City: the last of the goldfish from underneath the tuberculosis hospital.

It is the end of a journey for the Queens goldfish, though their beginnings remain a mystery: Some theorize they were washed under the building after flooding from Hurricane Sandy scooped them from private ponds.

When the hospital’s destruction was announced, activists associated with the abutting beach, Bay 1 of Jacob Riis Park, a longtime refuge for L.G.B.T.Q. and other marginalized people, began a grass-roots effort to save the fish.

Beachgoers scooped out as many fish as they could and demanded that demolition wait until the whole goldfish school could be spared. In response, New York City Health and Hospitals, which owns the Rockaway property and oversaw the demolition, contacted the fish rescue.

In New York City parks, fish rescues are rare, according to Bonnie McGuire, the director of the parks department’s urban park rangers. Fish that are released in park waterways most often do not survive, she said. “Goldfish — or any other domesticated pets — don’t belong in parks. Do not release any pets into wild areas,” Ms. McGuire said in an email. “It’s not good for the ecosystem or the pet!”

Ms. Prohaska arrived in Rockaway with nets, but the subbasement was too deep to reach the goldfish, she said. She set traps loaded with Italian bread and caught more than 100; large ones went to a private pond in Mount Vernon, and 50 or so fry went to a woman in Scarsdale, who declined to give her name. (“I would like to be the gold fish fairy,” she said, in a text message to Ms. Prohaska.)

The mission continued. Since September a contractor working on the site has methodically fished them out with baited traps, according to New York City Health and Hospitals. It will end when the final fish are delivered to Mr. Wiggins in the next week. They will live in a pond outside a nearby Catholic church, he said — the ones he can bear to part with.

“It’s not every day you find fish at your construction site,” Manny Saez, the vice president of facilities at New York City Health and Hospitals, said in an email. “But we’re happy they found a safe home.”