JUST WHEN YOU THOUGHT IT WAS SAFE TO GO BACK IN THE DESERT.

Byline: Eric Noland Travel Editor

LAS VEGAS - This city's latest sleight-of-hand trick was to create a marine environment 240 miles from the nearest coastline. But Las Vegas couldn't stop there. The competition for the entertainment dollar has become so intense on the Strip that a simple 1.6-million-gallon aquarium - featuring docile tropical fish swimming in lazy circles - would probably be considered a bit tame.

So a giant fish tank that opened in June at the Mandalay Bay Resort & Casino professes to be devoted to predators of the sea.

The logo for Shark Reef - which is just behind the tropical-themed hotel's wave pool and not too many steps from the casino - features a great white shark that appears to be opening its chompers for the latest attractive young woman served up by Steven Spielberg. And the publicity materials load up on adjectives of terror: ``dangerous'' aquatic animals, ``venomous'' radiated lionfish and coral catfish, ``ravenous'' water monitors.

Don't expect to see any grisly scenes of the deep, though. That's just the come-on. The man-eaters of the shark family, tigers and great whites, are not here. But the aquarium still has plenty to offer, including some intriguing design features. Besides, there's something to be said for the novelty of examining moon jellyfish smack in the middle of the Mojave Desert.

One of the best features of Shark Reef is a 30-foot glass tunnel built through the center of one tank. When you walk through here, the colorful marine life of the reef literally surrounds you.

Another room is built to look like the hull of a ship and is dimly lit. There is a glass section in the center of the floor, and most visitors stop abruptly when they approach it. Every instinct in your body tells you that one false step and you'll be in the drink.

And aren't those some pretty good-sized sharks lounging at the top of this tank?

``They're sand tiger sharks, about 6 to 9 feet (long),'' said one of the many youthful guides on hand throughout the exhibit to answer questions. ``They're completely nonaggressive. You could go in there right now and swim around, and they wouldn't come anywhere near you. The divers who go into the tank wear shark suits, but only for liability reasons.''

Absolutely no threat? The folks in promotions probably don't want that getting out.

Sharks, undoubtedly because of their prominent place in fiction and film, seem to be an endless source of fascination for the young visitors to this aquarium. At one of the first tanks, 18-inch blacktipped reef sharks share the environment with manta rays, and a number of kids pressed up against the glass. One shark accommodated them by swimming back and forth in front of the glass, gill slits quivering, eyes staring vacantly.

For those visitors and their parents, there was much else to see. The glass tunnel provided glimpses of 3-foot bonnethead sharks, whose flattened heads look like spades.

Another room had a petting tank, where guides instructed the young ones in the proper technique (no grabbing, no jabbing with sharp fingernails) for stroking a manta ray. The rays cooperated a little by swimming near the edge of the pool, but some spotted tropical fish were having nothing to do with this - they huddled in the middle of the tank, far from overeager hands.

Shark Reef's creators, who worked in conjunction with the Vancouver Aquarium, wanted to depart from the static information placards found in other aquariums and museums by employing higher-tech TV panels that deliver an informational program when activated by foot traffic. It seemed a flawed system, though: If you happen by in the middle of the program, there is nothing to identify the species you are observing.

In order to include a few deadly (and no doubt ravenous) reptiles in the exhibit, Shark Reef was designed to look like an ancient temple that has sunk into the ocean. So before you get to the domain of tropical fish and sharks, you walk through a Jungle Cruise-like world of crumbling stone and twisting vines.

One of the first creatures you happen upon is a saltwater crocodile, one of the most terrifying creatures on Earth. It's been known to spring from the water to snatch, drown and devour cattle, humans and other mammals wandering along the muddy edges of estuaries in Australia.

This one, obviously well-fed and thus not particularly menacing, was lying so still that it appeared to be in a coma. Or stuffed. But a nearby video exhibited the creature in all its jaw-snapping glory.

Establishing an ocean environment in the middle of a desert was no easy feat. The creators reportedly sent to Israel for a compound called Red Sea Salt. It is a dehydrated salt concentrate which, when introduced to filtered tap water from Lake Mead, closely approximates seawater.

For those who have visited the outstanding aquariums located on the California coast - notably at Long Beach and Monterey - Shark Reef will seem a poor cousin, though not priced accordingly. Its children's admission price is significantly higher than those fine facilities and the adult price is comparable. But it still has its merits, and while not particularly frightening, warrants a look.

IF YOU GO

Shark Reef, located at the Mandalay Bay Resort, is open daily from 10 a.m. to 11 p.m. Admission is $13.95 for adults, $9.95 for kids ages 5 to 11, no charge for children 4 and under. Information: [phone]; www.mandalaybay.com (on the home page menu, click on ``entertainment,'' then on ``shark reef'').

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Photo:

A glass tunnel provides an up-close view of fish and coral at Shark Reef, a new aquarium at the Mandalay Bay Resort.

Box: If You Go