LIMA, Peru - It's still dark on the streets, but sight is the least relevant of the senses when entering the open-air Villa Maria seafood terminal at 5 a.m. on a weekday.

The smell of fish, detectable blocks away, is strong enough to taste. Men with gravelly voices bark prices from the backs of ice-filled trucks, and water splashes with each step on the puddled pavement. Shoulders collide as people rush by on all sides, and sharp stabs of pain flare as the edges of two-wheeled pushcarts slam blindly into shins and calves.

“Here!” yells one of the vendors in the market, which occupies a full city block. “Good prices!”

At this hour, the customers are professionals - competitive buyers for supermarkets and restaurants who won't be seduced by such primitive pitches. They know what they're looking for: the truly good stuff that's usually long gone by the time the public shows up about 8. Lima is the world's capital of seviche, the Peruvian dish of raw seafood marinated in citric juices, and what happens in the dim light of this market can mean the difference between great lunches and culinary disasters.

Lucas Reto arrives at the market each day with a list affixed to his plastic clipboard. He is the buyer for one of Lima's most popular seafood chains, Segundo Muelle, and is responsible for determining what will end up on people's plates later in the day. In a white smock, white hat and knee-high rubber boots, he joins the masses without wasting time. He's been doing this for 12 years, and knows the golden rule: Fish don't keep. Every minute counts.

He examines a crate of sole, feeling the scales and running a firm thumb down the length of a few fish. The flesh is uniform, without soft spots - a good sign. And even though it smells like fish, it doesn't reek - meaning it's quality stuff. He tells a man with a calculator dangling around his neck that he'll take about 190 pounds of it.

“When I first started doing this,” says Reto, 47, “they'd all ask high prices and hide the good fish from me.”

Reto pays about $2.50 per pound - more than he'd like to, because he can usually get it for $2.25 or $2.30. He spots a buyer for a major supermarket chain, and they pause - for about three seconds - to commiserate about the seasonal inflation.

“If someone comes here and doesn't know what he's doing, who knows what price he'll pay,” says Reto, bumping through the crowd to check out another stand of crated fish.

All around him, men and women sift through clattering shellfish, squatting as if panning for gold. Buyers lift giant swordfish off steel tables and look into their eyes. Crabs in red crates wave their claws lethargically. A man pushing a crate of grouper hits a crack in the pavement and five fish slip onto the wet concrete; he groans and collects the fish. Reto sticks his hand into a crate of shrimp and says he'd like about 22 pounds. A minute later he's talking to a vendor of squid and baby octopus; the man pushes up the sleeve of his sweat shirt and writes Reto's order on his forearm with a ballpoint pen.

By 5:14, Reto is at the Zone of Filleteers, a collection of stainless-steel tables staffed by knife-wielding men and women with scrap buckets at their feet. Delivery boys have dropped off the fish he has bought at one of the tables. As the cutters slice the grouper, sea bass and tuna into fillets, Reto examines some of the crated fish again, relegating a few to a reject pile. Those fish are carted back to the vendors, where they will await a less discriminating buyer.

Reto handles the long fillets and packs them into plastic bags, taking care to keep them flat - they get rigid if they're folded or bent, he says. A man slices the head off of a giant tuna and goes to work on the meat. The table is drenched in deep red blood. Reto approves - very, very fresh, he says.

By 5:40, he's ready for a second round of visits to the vendors. The sky is lighter now, allowing clearer glimpses of the glistening wares on display. But Reto has done the bulk of his buying, and he seems satisfied that he didn't miss much. It's a quick circuit, and he's back to the fillet table within 15 minutes. He'll spend the next hour here bagging fish, before making delivery rounds to the restaurants. The rest of his morning will be spent in the kitchen, helping prepare the seviche and subjecting his purchases to the ultimate test: taste.

“I look at fish, then taste it, look at it again, then taste it again,” Reto says. “Then for lunch, I usually have a nice piece of beef.”