Michael Bailey is injecting each defrosted smelt with a syringeful of vitamin solution and explaining to a visitor how he discovered his metier.

"When I was a kid, I lived on an island off the coast of Massachusetts and I used to go swimming with a mask and snorkel," he recalls, opening a second one-pound bag of smelt. "One day I saw a shark swimming along -- it was beautiful. I used to watch Sea Hunt on TV a lot, too."

Bailey, now a grown-up marine biologist, is assistant curator of the National Aquarium in the basement of the Commerce Department. One of his duties is to feed the aquarium's sharks. Sometimes they get squid, sometimes beef hearts, but they like smelt best. Today, however, he's not sure they'll snap them up as aggressively as usual.

"The water in the shark tank is a little cold," he tells the crowd gathered for the thrice-weekly 2 o'clock feeding of the sharks. "Sharks are cold-blooded, so that means their body temperature has gone down. They probably won't be as hungry, aggressive or excited. I'll be feeding them smelt -- the same kind you buy in the grocery store."

With that, Bailey disappears into the narrow, winding passages behind the tanks. When he reaches the back of the shark tank, he takes a smelt from the bucket and holds it in the water with his bare hand.

"I'll feed them until they don't look hungry," he says, dropping the smelt. "I've only been bitten once, by a tiny shark I was trying to force-feed. Sharks in a feeding frenzy will bite -- I've even seen them devour their own intestines -- but I don't think sharks are as mean as people think.

"They might take a test bite and they might bite to defend their territory. In the ocean we might not know where their territory is. If there's a dog in a yard that's not fenced in, we might not know where its territory is, but the dog does. If sharks wanted to eat people, a lot more people would be eaten."

The sharks circle the meal, snapping up occasional morsels.

"They circle their food," explains Bailey, pulling another smelt out of the bucket. "They don't rely on vision until the very end. They have a lateral-line system -- they can feel vibrations. It's something like hearing in humans. They can also smell and sense electrical charges. If a shark swims over a flounder that's submerged in sand, it knows the flounder is there by its electrical charge."

After a leisurely half-hour meal, the sharks have eaten only about a quarter of a pound of smelt each, less than half their normal ration. But Bailey thinks they've had enough and starts distributing the leftovers to their neighbors.

"Hi, Spunky," he says, throwing a smelt to a green sea turtle he describes as a neat guy.

"Almost everything here will eat smelt. We try to duplicate each animal's natural diet, but we can't always. The rock beauty, for instance, eats live sponges. They're not easy to come by or to keep."

By the time Bailey has made his rounds and reappeared on the public side of the shark tank, most of the crowd has dispersed. But some hard-core shark fans are still watching the animals swim around.

"Aren't they pretty?" asks Bailey. "One of my favorite things is to go diving with sharks. I carry a little wooden dowel with a nail head in it to push them away with. Anytime you're in the ocean, you're an outsider in their domain."

Then Bailey excuses himself to go talk with a boy who wants to be a shark person when he grows up. WATCHING THE SHARKS EAT Feeding time in the shark tank is at 2, Mondays, Wednesdays and Saturdays. The National Aquarium is still in the basement of the Commerce Department, 14th Street and Constitution Avenue NW, but it's now run by a nonprofit society. It's open 9 to 5 daily, except Christmas, and may be reached through the 14th Street-building entrance. Admission is $1 for adults, 50 cents for children under 12. Admission is free for members, who also get a newsletter, discounts in the gift shop, opportunities to volunteer and invitations to lectures, collection trips, etc. Membership costs $10 a year for juniors, $15 for individuals, $25 for families. For $500, you can adopt a fish for a year.