Fish Story.(The Talk of the Town)(Larry Saul, blacktip reef shark)

How seldom the native of this, the most vertical of cities, actually turns his head skyward. New Yorkers tend to stare straight ahead or peer downward, the better to avoid strollers, puddles, dog droppings, and panhandlers. For the past few months, though, passersby near the intersection of Bedford and Morton Streets, in the Village, have been spotted with their heads tilted back. The object of their gaze: a large aquarium, visible through a second-story apartment window. The tank glows neon blue, like a sign outside a jazz club. Its tenant is not a goldfish or a guppy but, rather, what Jacques Cousteau called "the splendid savage of the sea." Even from the street corner it is clear: swimming in circles, interminably on the prowl, is a shark. The view, neighbors agree, is mesmerizing: Damien Hirst before the formaldehyde.

The pet shark. Apparently, people do this. Kevin Federline, after marrying Britney Spears, installed a shark tank in their house. ("It's probably like six hundred gallons," he told a reporter. "A flat-screen TV comes up in front of it. It's like a tropical paradise.") Nicolas Cage owned one, as did Ice-T, who reasoned, "All James Bond's best enemies had shark tanks." The former N.B.A. center Matt Geiger has kept sharks in a three-thousand-gallon tank in a house in Florida. The pet shark may be the new pit bull--the mascot of the outsized ego, the Hummer of the living room.

And so, up two flights to meet the big fish. Larry Saul, the apartment's owner, opened the door. Saul is not a rapper or an actor or a basketball star. He is a short, unprepossessing, forty-five-year-old child psychiatrist, with a good-sized paunch and a shock of frizzy white hair. Across the room, his wife, Lynn, who has just received a Ph.D. in psychology, flipped through the Times. Their six-year-old daughter, Georgia, played with Bernie, a chocolate poodle. "Sorry to disappoint," Saul said. "You were expecting a bachelor pad, huh? Maybe a rock star?"

The fish, a blacktip reef shark, was caught in Indonesia six months ago and supplied to Saul by his longtime fish guy ("I found him through my stereo-system guy"). Georgia had named it Black Fin. He is more than two feet long, and he glided ...