Something doesn’t add up on this blight-infested stretch of storefronts in Oakland’s Eastlake neighborhood.

The aquarium store doesn’t sell aquariums. The sports bar sits beneath a crisp new awning but never seems to open during posted hours. The cafe doesn’t advertise coffee, though the manager will make some if necessary.

The real draw, for those in the know, is the “fish game.”

On a recent afternoon, three men huddled over a bulky video game in the cafe, slapping a button as fast as their wrists allowed. The gamers’ eyes were fixed on a screen about the size of a pool table as they settled in for the long haul. One man sipped from a Big Gulp, another from a jug of watermelon juice cocktail.

The fish game looks like it came out of a first-generation arcade, with cartoonish sea creatures, joysticks and whimsical, blingy sound effects. But in this case, money was on the line. Every so often, an employee carrying a stack of cash paid out the winners.

Enthusiasm for the fish game has prompted a city crackdown on illegal gambling dens. Beginning in 2018, Oakland police opened long-term investigations into the gaming halls, attempting to root out operations they say are increasingly linked to robberies, assaults and shootings, including a homicide.

Officers have seized more than a dozen fish-game machines in at least 15 raids of unregulated casinos, according to interviews and an internal report provided to The Chronicle. But trying to shut the dens is like whack-a-mole. As soon as one goes down, police say, another pops up.

In a new strategy, city officials are leaning on landlords to evict tenants who profit from gambling. And investigators are going after the criminal networks that run the games.

“Four years ago, I would think this is a low-level type of incident,” said Capt. Kirk Coleman, who oversees community resource officers in the Eastlake area. “But the level of violence is eye-opening.”

Oakland, like many major cities, has a history of illegal gambling dens. From a SWAT team raid in 2016 to a “vice war” in 1927 that led police to arrest three men and confiscate 65 “gambling machines,” people have long thirsted for action in Oakland. Some places today operate speakeasy-style, others do business in plain sight.

Over the past two years, police say, much of the violence in the San Antonio and Eastlake neighborhoods can be traced to off-the-books businesses that feature the fish game, a colloquial term for a family of arcade titles that includes “King of Treasures,” “Ocean King” and “Fish Hunter.”

Investigators say most patrons are tightly knit regulars. If one shop shuts down, someone tells the players where the next operation will emerge. Sometimes it’s in the same spot.

Police have nicknamed the gambling dens “slapshops,” based on the noise of the button-pushing. Players park themselves around a game table and feed in bills for credits. The goal is to shoot fish, sharks, octopus and other sea creatures, aiming with a joystick and slapping a circular button.

Because the establishments deal only in cash, patrons and employees are often set upon by crooks. According to police, one confrontation turned deadly.

This month, a murder case is unfolding in court against Marshawn Chambers, 22, who is accused of fatally shooting 32-year-old Xin Hoang and injuring two others last year in a dispute that kicked off in an illegal casino on the 1100 block of International Boulevard.

Police say Hoang’s friend, Anthony Le, returned fire, sending at least three other people diving for cover between cars.

In April, a 52-year-old man was shot and another victim was pistol-whipped during a robbery at the same site, a shuttered hair salon. Investigators believe the suspect in an attempted homicide two months before that was either arriving at or leaving the “aquarium store” on East 12th Street.

Raids on the underground Oakland businesses recently netted at least 10 arrests for crimes that include robbery and illegal firearms possession, officials said. Search warrants yielded thousands in cash, payroll sheets and, of course, fish games.

A woman who works near two of the Eastlake shops said she and her son have witnessed prostitution and drug deals outside the operations. The woman said that the activity is driving away her customers, and that she may have to uproot her store.

“People don’t even want to come here anymore because they’re like, ‘Oh, you don’t know what you’re going to bump into,’” said the woman, who asked that her name be withheld because she feared for her safety. The Chronicle agreed in accordance with its policy on anonymous sources. “Cops are fully aware of what’s going on, but they’re telling us they don’t have the power to shut it down.”

Undercover officers staked out the “aquarium store” in April and watched a patron walk in and out the front door, according to court records. But when two officers attempted to enter, they were stopped by an unknown man asking who they knew. One of the officers said he was looking to buy aquarium equipment.

The doorman responded they were “out of business.”

Oakland Councilwoman Nikki Fortunato Bas, whose district covers the area east of Lake Merritt, said her constituents told her about the gaming shacks shortly after her 2018 election.

“Our understanding is that it is difficult to prosecute, and even when prosecution happens, these businesses can pop up again under new ownership,” Fortunato Bas said.

Closing the dens, she said, is a priority for her office. She pointed to an effort to identify irresponsible landlords by cops, city attorneys and the city administrator’s Nuisance Abatement Division. This spring, they started threatening legal action against landlords who rent to tenants with a history of “nuisance” behavior. The strategy is similar to one used to shut down illicit massage parlors.

On March 22, Greg Minor, an assistant to the city administrator, wrote a letter to a landlord demanding that she evict her Oakland tenant, Phap Nguyen, within 25 days. Nguyen was convicted in January of possessing or controlling slot machines at a property on the 1900 block of International Boulevard. The landlord complied.

Police and city officials are now going after several other locations. Last month, the owner of the aquarium store property received a notice that included a $4,904 fine and threatened penalties of up to $1,000 a day if the tenant wasn’t evicted.

“Hopefully, this will alert property owners to take more responsibility,” Coleman said. “We want this to affect the person who allows this to happen.”

Ivan Golde, a defense attorney who specializes in gambling cases and has represented clients accused of running fish games, has argued in court that gambling is a victimless crime.

“A couple people in a cafe are just playing nickel and dimes,” Golde said. “You don’t want to throw a guy in jail and put a record on him for playing 50 cents. Nobody cares!”

Oakland police, however, say the dens can pull in large amounts of cash, pointing to one raid that seized $50,000.

Operations like those in Oakland have sprung up across the Bay Area, including in San Francisco and San Jose, said Oakland police Sgt. William Febel. The gamblers come from all walks of life.

“Everybody plays,” he said.

Timothy Fong, co-director of UCLA’s gambling studies program, said the draw is usually convenience. The nearest regulated slot machines to Oakland are at a tribal casino in San Pablo, about a half-hour’s drive away. A quick trip to Eastlake can get a gambler in on the action.

Fong cautioned against lumping gambling together with criminal activity.

“Gambling is part of our lives. It’s what we do with our entertainment dollar,” he said. “It absolutely doesn’t mean that everyone who’s a gambler is a criminal, just like every criminal doesn’t gamble.”

The question, Fong said, is how much local and state governments should prioritize crackdowns on illicit casinos.

“Unregulated gambling,” he said, “despite all our best efforts, will continue to occur.”

Megan Cassidy is a San Francisco Chronicle staff writer. Email: megan.cassidy@sfchronicle.com Twitter: @meganrcassidy