"For Japanese, fish is the very best thing in the world," Sadao Ohashi declares with pride as he pushes his medieval-looking, two-wheeled wooden cart at jogging speed, maneuvering a load of mackerel, squid and sea bream through the moving maze of carts, people and battered one-man trucks that throng the slippery concrete vastness of Tsukiji Fish Market down by the Sumida River in Tokyo's Chuo Ward.

For deliveryman Ohashi, leaving for work around midnight from his nearby home is a bit like going into battle, weaving between fleets of trucks laden with produce fresh from seaports near and far. From then, till the time at which office workers start filing into the high-rises over the road, he's hard at work with his karuko, trundling the sea's bounty from the wholesale auctioneers' sheds to the stalls of some of the market's 1,200 middlemen fish merchants or delivery vans waiting to whisk his loads to supermarkets, restaurants and family-run fish shops all over Kanto.

Making a living at Tsukiji, the world's largest seafood market, is nothing if not hard work. But it's a challenge Ohashi, a grizzled 62-year-old with half a century's work there under his belt, is proud to rise to night after night, come rain, sun or snow. "I love fish, and I've been in and out of this market since I was a kid, so now it's part of me," he declares. "This place is always jumping and it's really tough work, but I'd never think of doing anything else. This is the life for me."

For Ohashi and the other 15,000 workers there, though, a job at Tsukiji comes with the distinction of being at the center of Japan's world of seafood -- indeed, its gastronomic heart. It is a 22-hectare hub where products come in, not only from across the Japanese archipelago, but from the four corners of the earth -- to be rerouted to every nook and cranny of the country.

Shipments pour in from around 5 p.m. and, for the next 12 hours, up to 17,000 vans from nearby ports and giant refrigerated trucks from further afield disgorge some 2,300 tons of seafood and 1,500 tons of fruit and vegetables, set to be traded for around 2.4 billion yen.

By the wee hours, buyers from the market's seven auction houses are busy doing multimillion-yen deals acquiring the catches from suppliers. Then, from around 4:40 a.m., bells start ringing as the noisiest phase of Tsukiji's day begins. Fish merchants start bidding, while auctioneers rattle off prices in what sounds like a high-speed Buddhist chant.

Tuna are the prize commodity. The giant fish, ranging in size from 50 kg to 200 kg, typically fetch from 1,000 yen per kg to well over 10,000 yen per kg for the best quality. Prior to the auction, the buyers have examined the mighty carcasses lined up on the concrete floor, their icy bodies filling the sheds with clouds of vapor. The auction houses prepare the fish for inspection by hacking off their tails and pouring on boiling water to soften the flesh. An incision is made to allow the middlemen merchants to feel the flesh and so assess the quality of a specimen, judging the price they'll be prepared to pay. If the tuna is fresh, not frozen, buyers rub their fingers over sample slices, feeling for texture and oiliness, with the oilier specimens being most prized.

In arriving at their assessments, both with tuna and the hundreds of other types of fish in the market, the buyers have only their own experience to rely on, with big money -- and their reputations -- at stake. As Ohashi put it, "Choosing good fish is an acquired skill, and to know a good one from a bad one with only a glance takes decades."

After purchase, the fish is prepared for retail by the middlemen. Two-meter-knives and motorized saws are used to carve up the carcasses -- stall holders missing a finger or two are not an uncommon sight. Come 7 a.m., the fish has been packed and priced, awaiting shoppers and sightseers. Their arrival means Tsukiji's business for the day is nearly done.

A time capsule of the past, home to an age-old commerce and housed in buildings dating from the early postwar years, the market correctly known as Tsukiji Jogai Shijo (Tsukiji Outside Market) is a microcosm with its own social order unfamiliar to those who live and work outside its walls.

It is, though, a world that's fast fading away. Japan's decade-long economic slump has eroded demand for high-quality fish, squeezing profit margins throughout the industry.

In a bad omen for wholesalers and retailers alike, the top price paid for premium tuna on Jan. 5, the first day of business this year, was 13,000 yen per kg -- about half the expected rate at the start of a year. An array of other fish prices are also at seabottom levels. "There was a time when tuna was regular fare. But with times being so tough, lots of consumers are buying cheaper fish like sardines, mackerel and salmon," lamented Noboru Nagashima, a market worker with 30 years' experience. "For us guys on the ground, that means lower salaries, staff reductions and bonus cuts."

However, faltering demand isn't the only problem. Streamlining in the notoriously complex distribution system has allowed some retailers to bypass middlemen and buy seafood directly from wholesalers. This combination of factors has put shoals of fishmongers out of business.

Nonetheless, economic doldrums haven't detracted from the market's grimy charm. Every year around 8,000 tourists -- many from abroad -- grab their cameras and take their chances with the carts and trucks and trolleys to get a glimpse of the market's inner workings. Visitors planning some creative home cooking can haggle with merchants hawking just about every kind of creature that swims. Those with a penchant for local seafood can choose from saury, squid or urchin, to name just a few. Among the more exotic delicacies from overseas are yellowfin and bluefin tuna from the Gulf of Mexico, shrimp from Indonesia, sea bass and sea bream from Chile, salmon from Alaska, lobster from New England . . . the list goes on and on. In all, there are said to be more than 400 varieties of fish on sale.

Although seafood from distant parts of the globe, such as Sweden or India, comes frozen solid, plenty of produce arrives still very much alive and gasping, snapping or flapping as it awaits the chop of a blade or a dip in boiling water. In short, fish doesn't get any fresher. On the market's outer perimeter, meanwhile, is the often overlooked fruit and vegetable section, where boxes of mandarins, apples, radishes, cabbages and onions are piled into mountains.

Anyone who strolls beneath the rusted awnings can sense Tsukiji's history. Built along the river on reclaimed land, the market was opened in 1935 after its predecessor in Nihonbashi was leveled in the Great Kanto Earthquake of 1923. Perhaps the biggest shock to follow that tremor came in 1954, when the Japanese fishing boat Lucky Dragon V was exposed to radiation from a U.S. hydrogen-bomb test at Bikini Atoll in the Pacific. The crew members, one of whom later died, returned to Japan unaware they and their catch had been contaminated. The fish were about to be sold at Tsukiji when radiation was detected in a last-minute check, and the haul was buried near the market's entryway.

Today, age and obsolescence are perhaps the biggest threats to Tsukiji's current premises. Crowding remains a problem and amid the rush there are hundreds of injuries and fender-benders a year, said Ken Kotani, a Tsukiji security manager. Nobody in Tsukiji's macho world even bothers to count the collisions between the one-man trucks, which are built to take such abuse anyway, he said. The facilities are so overextended that business spills onto the surrounding main roads and side streets every morning. With nowhere else to work, drivers park their trucks and vans anywhere they can.

To reduce this congestion, as well as to create a market with 21st-century facilities, on Dec. 25 the Tokyo Metropolitan Government officially announced that by 2015 it will relocate Tsukiji to a more spacious site in the nearby Toyosu Wharf area of Koto Ward. The proposed move has been welcomed by market officials, who say it will not only make Tsukiji a safer place to work, but also save the city money, increase efficiency and help the market to maintain its position as Tokyo's main center for trade in fresh produce.

But the decision is far from popular with rank-and-file workers and some of their best customers, namely the managers at high-class ryotei restaurants just a short walk away. For those most attached to the aging market, the move symbolizes all that is unsettling in the industry's push toward modernity.

"Yes, the land over there may be cheap," said market worker Nagashima, referring to Toyosu. "But this place is just fine for all of us here."