THEY SAY no one has ever seen a rusted blackfish hook.

Because blackfish are so difficult to catch, spending most of their lives darting in and out of the crevasses and crannies of underwater wrecks and reefs, they have developed a reputation for getting hooks snagged on the structures. Anglers at the surface feel the sharp pull of a blackfish one moment, then the steady weight of the bottom the next. The only recourse other than to spend time wiggling the hook free is to snap the fishing line.

A day fishing for blackfish could mean losing a half dozen or more hooks. It can be frustrating, but when a fish is pulled up from the sanctity of the bottom, it seems worth the investment.

"It's probably the most challenging fish in the ocean as far as I'm concerned," said Mike Barnett, owner of Codfather Charters out of Freeport. "It takes a long time to become a good blackfisherman. It's not something you can learn to do really well on just one or two trips."

Barnett has been doing it since 1975 and has established his business as one of the premier blackfishing charters on the South Shore. He used to spend most of his time from fall to spring fishing for cod - thus the name of his boat and business - but as the cod numbers have slowed over the past decade, Barnett has nudged most of his clients to blackfishing.

"I still get a lot of calls for cod, but I just don't take them," Barnett said. "I tell people we have a good shot at catching as many cod as a bycatch from blackfishing as we would if we targeted them."

Blackfishing is an entirely different experience on the North Shore as compared to the South Shore. Geology makes it so. Long Island Sound's bottom is covered with rocks and boulders left behind by the ice age, making large areas fertile grounds for the tog. Blackfish can even by caught by surfcasters off the beaches.

On the South Shore, however, there are very few natural structures. The key to fishing in the ocean is to position the boat properly over a wreck or a man-made reef. Two anchors are almost always necessary for this, and a few feet in any direction can mean the difference between catching fish and catching nothing. Typically, if the boat is positioned correctly, the first bites will come right away, providing a gauge of the captain's dexterity with the anchors.

The difference between hitting structure and not can be so slim, in fact, that fish can be caught on one side of the boat while no fish are caught on the other. When blackfishing, it is not a breach of etiquette to muscle in on someone else's space on the boat.

The bait that works the best for blackfish is a green crab, broken into small bits so that a piece of shell stuffed with meat is plied to one of those shiny new hooks. Dropping the hook to the ocean floor, it usually doesn't take long for that first hit from a blackfish. It is the inexperienced angler who tries to set the hook on that first nibble.

Blackfish have two rows of teeth in their mouth, which makes setting the hook very difficult. Catching a blackfish requires the patience to wait for a third tug from the prey before lifting the tip of the rod and reeling.

"Most people hit on that in-between, when the hook is between the front and back teeth, and he just opens his mouth and out comes the hook," Barnett said. "You have to hold back and let him eat more than you let just about any other fish. And they have a rubbery mouth, so to hook them you have to hit them hard."

The first six feet are critical to catching a blackfish because it will instinctively try to get back to the safety of the structure, taking with it the fishing line and tangling it around the rocks and other characteristics.

Blackfish are not unlike the groundhogs at the amusement park game, popping in and out of holes in search of food. Lifting and reeling very quickly for the first six feet or so will prevent the fish from diving.

On the other hand, there are times an angler feels nothing. Even the weight of the lead sinker disappears. That's a signal to start reeling really, really fast. It could mean that a huge blackfish has taken the bait and is swimming toward the surface.

Blackfish, also known as tog because of their proper name, Tautoga onitis, have been under tremendous pressure by commercial and recreational fishermen for the past decade. They have become a hot commodity at fish markets, fetching high prices as a delicacy. In an attempt to rejuvenate the population, the state Department of Environmental Conservation has regulations to protect the tog. Recreational anglers are allowed to keep 10 fish that measure at least 14 inches between Oct. 7 and May 31. From June 1 to Oct. 6, recreational anglers can keep one 14-inch fish per day.

"Years ago blackfish had a stigma of being a boney fish and nobody liked to eat them," Barnett said. "People are now realizing it's a very good eating fish. All it eats is shellfish, no other fish, and that translates into good white meat."

Good eating that is worth the challenge.

For information on chartering the Codfather for blackfishing or any other trip, call Mike Barnett at 516-868-9073 or visit www.ufish.com/codfather.