The Mirage, which is where Castaways once stood, features a 16,000-gallon aquarium behind the lobby's front desk. There are about 500 tropical fish and a SpongeBob SquarePants figure in it but no naked women. Still, it's a major attraction, even drawing tour groups through the lobby, says Yen Vuong, director of The Mirage front desk.

Naked women aside, what's the appeal of aquariums in casinos?

Dennis Wightman knows from designing aquariums for a living that people do, in fact, like fish but the reason why remains a mystery to him.

"I don't know what the fascination is," he says. "Maybe it's that you're looking into something you can't touch but you can see it. And it's always changing."

People often think of aquariums as interactive pieces of art, says Wightman, a designer for Acrylic Tank Manufacturing. The company has built many aquariums found in local casinos, including Bellagio, Mandalay Bay, The Mirage and Golden Nugget. An aquarium replaces a piece of hanging artwork and, because the interior can be changed and fish swapped out, it's versatile, he explains.

Watching fish swim calms some people, he adds, and the colors, shapes and designs are pleasant to view.

"It's an aesthetic thing," he adds.

Activity swirls around Sara Maklin of Indiana as she waits to check out of The Mirage on a recent Wednesday. But, wearing a tranquil expression and a wistful smile, she appears to be in another world as she watches the fish swim back and forth in the aquarium.

"It gives you something to look at while you're waiting," Maklin says. "It takes your mind off the line."

That's not surprising, because research on fish-gazing has been shown to induce relaxation. That could be one reason aquariums are found in so many hotels, Green says. Also, the tanks may trigger the nostalgia of guests who once owned aquariums.

"One truism is that Las Vegas is never so edgy that we make you that nervous," Green says. "I do think it's trying to create an atmosphere. ... I think it's relaxing and might remind you of home in certain ways."

"Water in general is very tranquil," says Nick Davi, Mirage aquarist and interim aquarium director. "You just see these fish that captivate you. I think it puts people at ease."

The Mirage aquarium serves as a focal point in the lobby, Vuong says, and gives front desk clerks and guests something to talk about during transactions.

Mirage employees always knew the aquarium was well-liked but they didn't know the extent of its popularity until it was closed for cleaning from July to October. Guests and visitors were surprised to see it draped with a black curtain, says Brittney Jones, a front desk agent.

Employees got into the habit of reassuring people that it was, indeed, coming back and in the meantime, they could go to Mandalay Bay to satisfy their fish craving, she notes.

"It's a big part of us," Jones says, adding that guests routinely ask what her favorite fish is, how much they eat and whether they have names. As for the answers, the porcupine blowfish is everyone's favorite fish, she says, because it follows people as they walk past the aquarium. Though she doesn't name the fish, Jones says some front desk people do.

And how much they eat depends on the fish, but they receive twice-daily feedings six days a week. Some of the carnivores eat pieces of chopped fish while the herbivores eat plant-based fish food, Davi says.

"The guests love (the aquarium)," Jones says. "It keeps them occupied."

Contact reporter Sonya Padgett at spadgett@reviewjournal.com or (702) 380-4564.