"We won't have to go to a public aquarium after this," says Mr. Cohen, 38 years old, a beauty-supply importer who is spending about $400,000 on the tank.

>From a New Jersey businessman building a 20-ton coral reef in his cigar room to the rock singer who bought Shaquille O'Neal's home for its predator tanks, some fish-loving consumers are starting to create at-home versions of Atlantis. Inspired by resort aquariums and spurred by technological advances in the $3 billion aquarium industry, homeowners are building megatanks in unconventional shapes like arches and racetracks. They're also shopping for equally exotic -- and pricey -- fish and coral. Meanwhile, sharks and piranhas have become so popular as pets, the Monterey Bay Aquarium says owners now call at least once a week offering to donate fish species that have gotten too big.

While most of the growth is in expensive tanks, some of this is trickling down to regular homeowners. PetsMart's biggest aquarium, which costs $475, is now 150 gallons, up from 75 gallons a few years ago; later this year, some of the retailer's stores will start stocking a 110-gallon model with upscale cabinetry for $1,000. Petco has recently expanded its line of fancy cabinet finishes for bigger tanks. Even custom builders are reaching out to a slightly broader audience: Living Color Enterprises, an aquarium company in Fort Lauderdale, Fla., has just introduced its first line of $13,000 ready-made tanks about the size of a big-screen television.

Often, the public is soaking up what it sees on visits to public aquariums and hotels. Almost half of the country's 37 aquarium attractions opened in the past 15 years, and many tout their tank size. (The Georgia Aquarium in Atlanta, which opens in November, boasts of having more than eight million gallons of water in its tanks.) More than half a dozen Las Vegas hotels have added "aquascapes" to their properties during the past few years, and about five million visitors have paid $16 a head to see Mandalay Bay's Shark Reef since it opened in 2000. The centerpiece of the newly opened Hotel Victor in Miami: a tank of jellyfish that get fed frozen shrimp by a visiting caretaker.

Bubbling Up

Americans have long been fans of fish. One in seven American households has an aquarium bubbling at home, and consumers own one-third more fish than they did a few years ago, according to the American Pet Products Manufacturers Association. But up until recently, nearly all fish tanks sold had glass walls, and maxed out at about the size of a coffee table.

Now, though, the industry is switching to acrylic walls, which allow for more flexibility in shape and size than glass. Casco Group, an aquarium manufacturer in Cerritos, Calif., recently bought an oven so it could heat and shape sheets of acrylic up to 28 feet long -- three times longer than its old heating methods could handle. What's more, new filter systems use bacteria-laden sand (instead of gravel), which makes it easier to sustain tank ecosystems. And chillers, which keep tank water cool, have shrunk to the size of microwaves, down from toy-chest dimensions of a generation ago.

Those developments allowed Bob and Joyce Johnson recently to install a 9-foot-long saltwater aquarium that divides their breakfast nook from the living room. "I thought it would look dramatic," says Mr. Johnson, a documentary producer in McLean, Va., who spent $40,000 on the project.