The man at the fish store said his shad filets represented a technological breakthrough. "These shad were boned by a brand-new, $4,000 machine up in Baltimore Market," he said.

Okay, so guys clomped around on the moon, they can photograph a bullet in flight, farmers are producing 200 bushels of corn an acre. But a machine to bone shad, the fish with the most mysteriously complicated bone structure on earth?

"Sure, we've got two of them," said Tom Spencer, who works at Lou Foehrkolb Inc., among the top boned shad producers at the Baltimore Fish Market. "One's named Tony and the other's named Gary."

Tony and Gary looked up wearily from piles of fish flesh and grunted hellos. The sun was breaking outside and they'd already put in four hours. "Shad season's the same as always," said orange-haired Gary Mullins, who colleagues say is the fastest shad boner in town. "A 100-day sentence at hard labor. You couldn't get a machine to do this."

It is now the height of one of the mid-Atlantic region's great culinary seasons, with roe-filled shad making their spawning run up Virginia's rivers and the run already past peak in North Carolina. Fifty-pound boxes of iced shad arrive by the tractor-trailer load daily at Foehrkolb's and a dozen other wholesale outlets in the Baltimore Market, which moved a year ago from the old downtown marketplace to the suburbs here.

It makes for the market's busiest time of year, with Washingtonians in particular pressing ceaseless demands on the merchants for shad, shad and more shad. "I don't know why," said Lou Foehrkolb, 31-year-old proprietor of the stall named after his dad, "but the demand comes mostly from Washington. Baltimore doesn't use much shad."

The demand is met by an assembly line strategy at Foehrkolb's, which is as close to mechanization as shad production gets.

The slabs of pale meat are prepared in advance by Jack Leonard, who strips the roe from the whole fish, and by whoever else is available to do the scutwork of scaling and splitting the whole fish. Mullins and Tony Malanowski arrive as early as 2:30 a.m. to tackle the final, delicate task of removing the shads' multitudinous bones.

There is no boning machine in sight, of course, "and there never will be," said Foehrkolb. "But if there was, I guarantee it would cost $40,000, not $4,000."

There will never be a machine to bone shad because the wretched fish is so complex you can't even find two people who bone it the same way. Mullins and Malakowski, standing side by side, look as if they're working on two different species. If one starts at the wide end of the filet, the other starts at the narrow; if one removes the entire center spine, the other leaves half of it intact; if one spins his cutting board, the other keeps it stationary.

Then the boss, Foehrkolb, shows his technique, and it's different still. "Lou's the best," said Spencer, "but he's so particular he can't get any production. When we take boned shad home, we always take Lou's because it's really boneless. Tony's shad we call the Heimlich Maneuver special."

The problem is that while shad has a normal backbone and standard ribs to protect its soft innards, in addition it has two rows of free-floating, L-shaped bones that run not quite the length of each filet above and below the center line, the same as its little brother, the herring.

It takes a practiced eye and a trained hand just to find these free-floating rows, after which each shad boner makes his own path. The final product contains about a dozen knife cuts and looks like a bypass surgery victim before the stitches.

"The only way you learn," said Mullins as he carved his 1,000th filet of the day, or thereabouts, "is practice. I started out scaling. Then I cleaned the innards . Then they had me cutting the outside ribs.

"Then, late in the season when the fish were plentiful and cheap, I started trying to bone them. You know, you watch, you give it a try. I'd say I threw away about 600 pounds of fish."

It's a dying skill, said Foehrkolb, because even though he's plenty willing to teach it, "people just don't want to work that hard anymore."

Foehrkolb once was flown to Oregon by a market owner to train fish cleaners in the fine art of shad boning. "I did manage to teach one lady," he said. "I spent three days with her, and she could just about handle it if I stood right there and watched. But I don't think she could have done it if I wasn't there.