When the spring fishing season opens April 1, dozens of fishermen in northern Maine will pass over the traditional trout and salmon for a toothy invasive fish called muskellunge.

“They’re a very aggressive fish. They’re heavy. They’ve got razor-sharp teeth,” said James Daigle of Madawaska, who has caught record-sized “muskies.”

“There [was] nothing like that in the lakes around here,” he said.

Muskies are native to the Great Lakes, where they’re a top predator and one of the most sought-after sport fish – known as “the fish of 10,000 casts” because they are so hard to bring in.

Here in Maine, however, biologists and fishermen worry that the muskellunge that now inhabit Glazier Lake and most of the St. John River could make their way south to ruin some of the only natural trout and salmon fisheries left in New England.

The fish was introduced to Maine 34 years ago, when the government of Quebec, without the consent of American biologists, stocked Lac Frontiere, a border water that meets the St. John River near Daaquam.

Rumors of muskies in Maine started as early as 1973, but the state didn’t get its first specimen – a 20-inch fish caught in the St. John River – until 1984. Muskies were found in Baker Lake two years later, and in Glazier Lake by 1992. The fish are now thriving in the St. John all the way to the tidal waters of the Atlantic. They’re even using salmon passageways to get past a large hydroelectric dam in Mactaquac, New Brunswick, according to recent radio-tag studies conducted by Canadian biologists.

Today, St. John Valley people tell fish tales of huge muskies eating smaller salmon and trout off their hooks, pulling ducklings off the surface of the water, and nipping at fingers and toes in the local swimming holes. One fisherman brags that he doesn’t bother keeping muskies that weigh less than 12 pounds.

This winter, state fisheries biologist Dave Basley surveyed ice fishermen on Glazier Lake, and found that muskies, not native whitefish or lake trout, were the most common catch.

“People are reporting catching muskies in the same places they used to catch trout,” Basley said. “The fisheries are changing.”

Historically, northern Maine’s lakes and rivers have provided the clean, cold water that sensitive trout and salmon species need to survive. As a result, the area had developed an international reputation among fishermen.

But muskies are voracious feeders, eating the same small fish that trout and salmon rely on, as well as the native fish themselves.

“They eat most anything that they want to,” Basley said.

And a well-fed muskie can exceed 3 feet in length, and lay hundreds of thousands of eggs every year, he said.

Though Basley can’t put a number on the muskellunge population, anecdotal reports from fishermen suggest that it’s growing.

When Allan Albert of St. Francis caught his first muskie, he didn’t know what to call it. Today, he guides for fishermen who travel to Aroostook County to seek muskellunge, and they find plenty of them. A muskie sport-fishing industry in northern Maine isn’t too many years away, he said.

“All of a sudden, there’s been an explosion,” he said.

Although Albert is one of the fish’s biggest fans, he is also a trout fisherman who joins Basley in worrying about where muskies might end up.

Right now the Allagash Falls are keeping the fish out of the Wilderness Waterway, and Tinker Dam is protecting the Aroostook River. But the Fish River chain, which includes Long, Cross, Eagle and Square lakes – all ringed with fishing camps – is protected only by the 10-foot-high Lower Fish River Falls on the outskirts of Fort Kent.

Muskies are “knocking at the door,” Basley said. And the Army Corps of Engineers recently issued a report, in cooperation with the state, saying that muskies probably can make the jump.

“If they do get over the falls … it’s a scary thought,” Albert said.

This summer, the Department of Inland Fisheries and Wildlife will begin discussing whether an artificial barrier at the falls, which could cost tens of thousands of dollars, is necessary.

For now, DIF&W has refused to recognize the invader as a game fish, in hopes of keeping the muskies from colonizing new waters. Fishermen can keep as many muskies as they can catch, and the department even expanded the season well into last fall in hopes of knocking back the population.

Advertisements for muskie fishing are starting to sprout up in outdoor magazines, however, and Basley fears that political pressure to manage the fish for sport is beginning to grow.

If biologists don’t gain control of the muskie situation soon, the state someday may have to recognize the invader as a game fish, as it did with smallmouth bass and northern pike once their populations grew out of control, he said.

“I’m afraid that in 20 years, they’ll be all over the state, just like smallmouth bass,” said Jeff Reardon of Trout Unlimited.

Basley is focusing his efforts on educating fishermen, so they don’t boost the muskellunge expansion by transferring the fish in their bait buckets.

But like milfoil, muskies can’t be eradicated. The state’s only option is to keep the invasive fish contained to as small an area as possible, he said.

“They aren’t fish that we would have put into the river system, but now we have to live with them,” said Basley.

“They aren’t going away.”