The Inbursa Aquarium has 48 exhibits with thousands of specimens distributed in five big tanks and many other ponds. (Tomas Bravo/Reuters)

Pretty much everyone in this earthquake-prone megalopolis of 20 million can tell you the last place they want to be when the Big One hits.

And here, three stories below the street, there is a new horror to contemplate: the brand-new, subterranean Acuario Inbursa, Mexico City’s first aquarium and perhaps the only place in the world where it would be possible to be trapped underground and attacked by a shark at the same time.

Not to fear, said aquarium spokesman Victor Osuna.

“Safety was the first thing our designers thought of,” he assured, noting that the shark-tank glass is eight inches thick. “This place was built to withstand a 10.0 on the Richter scale.”

Named for its corporate sponsor, the Inbursa insurance company, the aquarium opened to great fanfare this month and is billed as Latin America’s largest, at least in terms of the number of species on display (230). Visitors enter at street level and descend three floors to undulating, mood-lit tanks that mimic the ocean’s depths.

Then they gradually ascend to brighter environs: shallow tropical reefs, beach ecosystems and fresh-water habitats like the Amazon River, exhibiting piranhas and crocodiles in turbid lagoons under a canopy of plastic foliage.

Of course, there is also the standard gallery of psychedelic jellyfish, back-lit and squirting around to woozy trance music.

“They’re sparkly,” said 4-year-old Santiago Vasquez, seeing one for the first time. “They look like flowers.”

This was precisely the idea, Osuna said: to teach city kids to love and respect the oceans and seas. Mexicans are fond of seafood, of course — the aquarium site was formerly occupied by an oyster bar — but they have not been the best stewards of their coastal waters, he added.

“We have very little culture of marine conservation in Mexico,” Osuna said.

The sprawling capital had elaborate canals and waterways in the Aztec era, but modern Mexico mostly dried them up. And while Mexico City is famous for its art and anthropology museums, the nearest aquariums were on the coasts in Veracruz and Mazatlan.

The Mexican billionaire Carlos Slim apparently spotted an opportunity in this deficit. He is a principal investor behind the $20 million project, and the aquarium sits directly across the street from the Soumaya Museum, which is named for Slim’s late wife and houses their art collection.

Slim cut the ribbon June­­ 11 alongside Mayor Miguel Ángel Mancera.

But while Slim’s art museum is free, the for-profit aquarium has a $10 entrance fee, putting it out of reach for many Mexican families. Perhaps more jarring is the visual contrast between the soaring, silvery facade of the Soumaya and the dull, cheap-looking exterior of the aquarium, which does not even offer visitors an awning for shade or rain while they wait in line. The bathrooms are not finished yet, either.

At least the aquarium’s other plumbing appeared to be working as intended. To fill the underground aquarium tanks, trucks hauled in nearly 6 million gallons of seawater. An elaborate network of filters recirculates the water five times a day.

“Every one of these animals requires a different care regime,” said veterinarian Damian Rojas, “but the system we have installed allows us to attend to the needs of every species.”

The subterranean design means that none of the animals will ever see the sun, but Rojas said most of the specimens were bred in captivity, not captured, and will be perfectly healthy with artificial light.

The aquarium plans to grow coral in its tanks, to be used to “reforest” dead and dying tropical reefs in Mexican waters, Osuna said.

Some of the tanks make innovative use of the aquarium’s unusual structure. Black-tip sharks swim circles around the enormous concrete columns that support the upper floors, sharing the “sunken ship” exhibit with ersatz anchors, a fake whale skeleton and a chesty wooden mermaid.

There is also a glass tunnel where visitors can pose for selfies with manta rays, and a grotto where teenagers can smooch in the low light.

Smaller children and their parents were clearly wowed, but the aquarium seemed to disappoint many young adults, especially those who had visited bigger versions up north. Its ambitions did not seem to match the great fortune of Mexico’s biggest fish, Carlos Slim.

“I’ve been to the one in Boston, and that one has penguins and seals,” said Cassandra Cortez, 21. “I expected a little more.”

While the exhibits at large U.S. aquariums tend to re-create entire ecosystems, the tanks at Acuario Inbursa toss together species from all over the world. Some were still waiting to be filled, so the crowds gathered at the touching pools where kids could handle rays and starfish after cleaning off their city germs with special hand sanitizer.

“This place is awesome,” said Rodrigo Ramírez, 9, whose family drove him nearly two hours from Cuernavaca, where he has his own fish tank. “I want a shark,” he told his mother.