Angler Jack Clements has fished the waters of Utah Lake near Provo since he was 8, yet more than half a century of experience couldn't prepare him for the catch he snagged last month.

"I knew it wasn't quite normal," said Clements, 62. "But when we got it out, my son said, 'Hey, Dad. Watch out! That's a piranha. It's got teeth.'"

Sure enough, the 11-inch fish Clements caught had choppers — lots of them — but this was no meat-eating piranha.

It was one of its vegetarian cousins, the pacu, a generic name for several species of South American river fish that can grow to be 30 inches long and sell for around $6 each at pet shops.

Clements wasn't the only fisherman with the ultimate fish tale.

In June, an angler brought a similarly ferocious-looking creature into Jim Tourtillott's bait shop in Dollar Bay, Mich., in the state's Upper Peninsula near Lake Superior.

The two fishermen thought they'd caught the terrifying piranha of B-movie infamy. But in both cases, natural resources officials identified the fish as pacus and determined they were most likely released into the wild after being in somebody's home aquarium.

More and more pet fish are being released into the nation's streams and lakes, officials say, and that has experts just as concerned as if they had actually discovered the school of Amazonian flesh-eating monsters that devoured scantily clad women in the 1978 horror film "Piranha."

"They don't have to be scary species — big frightening things like piranhas," said Scott Root, the conservation outreach manager at the Utah Division of Wildlife Resources. "Fun, cute little things can do just as much damage."

A Growing Problem

A quarter of all the non-native fish in the nation's waterways get there from aquarium dumps, said Pamela Schofield, a fish ecologist at the U.S. Geological Survey in Gainesville, Fla.

Her agency maintains a database of non-indigenous aquatic species and received 11 reports of pacu found in waterways nationwide this year, excluding the Utah and Michigan finds.

"There's no causal link," she said. "We didn't see the individual dump their aquarium fish into the pond or lake, but if you're catching a fish like a pacu, it's probably coming from personal aquaria because that's a fish you see in the aquarium trade and not, generally, in other aquaculture."

The remainder of the invasive species that make their way into waterways are from the aquaculture industry, escaping farms during hurricanes and floods, according to Schofield.

"It's a particular problem in South Florida," she added, "because once a non-native fish gets into a canal, you can imagine — it's just like a little non-native fish highway."

Fanged critters aren't the only ones keeping ecologists up at night with worry.

Zebra mussels, which hitched rides from the Black Sea to the Great Lakes in the ballast water of seagoing shipping vessels, are clogging lakes as far inland as Oklahoma.

Officials have littered the East Coast with flyers pleading for the mass slaughter of the snakehead fish, a native of China that can decimate native fish populations.

"We're fearful of other snails, little mitten crabs, little other crustaceans that have the potential to survive in the wild and be able to really wreak havoc with the natural fish and animal communities," said George Madison, the fisheries supervisor at the Michigan Department of Natural Resources for the Western Upper Peninsula in Baraga, Mich.

However, it's that most popular variety of aquarium pet — the goldfish — that's the most frequently released and can do some of the worst damage to native fish species.

"Oftentimes people think, 'Well, gee, if I just dumped in one fish, that's not going to make a difference,'" Schofield said. "But it can with goldfish because of the way they eat — they root around in the sediment and that suspends the sediment up in the water."

That, in turn, leads to murky water, destroyed vegetation and water turbidity, she said, adding that it can also disrupt the reproductive cycle of darters and minnows, whose eggs can get buried in silt.

Aquarium dumping is a significant problem, agreed Dean Wilkinson, invasive species coordinator at the National Oceanic and Atmospheric Administration (NOAA) in Washington, D.C.

"When you talk about aquarium dumps, you're not talking solely about your fish," he said. "They also can include particularly invasive plants, but you also have things like snails, which can be invasive and/or carry diseases for which they may be one of a series of hosts for the life stages of, say, a parasite."

Dumps tend to occur more often in the vicinity of transient populations, such as university campuses.

"We've seen it in other areas, near Air Force bases, military bases ... when people leave after a short term, they want to release their fish or their animal to a wild environment," Madison said. "It's a human tendency: They don't want to kill the poor thing. They want to do something that's humane."

Mystery Snails and Killer Algae

At Utah Lake, the largest freshwater lake west of the Mississippi, the pacu catch worried the state's wildlife resources division.

"It's the only place in the world where we have an endangered species called the June sucker, a little sucker-mouth fish that's been here for thousands of years," Root said. "Bottom line, we have an endangered species in this lake, so we don't like the fact that people are putting fish that grow too big for their aquarium into our bodies of water."

In the case of the pacu, a species used to an Amazonian climate, the first cold snap usually kills them. But both pacu and piranha have also established themselves in warmer southern states like Florida.

Cold hasn't stopped another predator in Madison's watershed, a 2- to 3-inch snail he called the "mystery snail." It's no mystery where it came from, however.

"It's a large aquarium snail, also from the pet industry," Madison said. There are several species of mystery snails, all hailing originally from Asia.

Regional infestations pale in comparison to two species, introduced through aquarium dumping, that are threatening the East and West coasts — lionfish and a substance known by some as "killer algae," caulerpa taxifolia.

The lionfish, which originated in the Indian Ocean, is the first non-native marine fish to settle a colony in American coastal waters, Schofield said. They're found along the Atlantic coast from North Carolina to Florida.

"Lionfish are a beautiful fish, but they're also toxic — they've got toxic spines which can sting people," said the NOAA's Wilkinson. "They also are sort of a top-level predator in their native ... reef systems."

Government officials breathed a collective sigh of relief last month, when a six-year eradication project targeting killer algae along the California coast was deemed successful.

Caulerpa taxifolia, a common aquarium plant that grows naturally along the Brazilian coast, was introduced into the Mediterranean Sea and now covers 50,000 acres. U.S. officials were worried the California outbreaks could cause the same.

"It overgrows things," Wilkinson said, noting it only takes a small piece of caulerpa to start a new population. "It has another competitive advantage in that it produces a toxic substance which discourages herbivores."

The approximately $7 million eradication project could have been spared if someone hadn't poured out the contents of his aquarium in the first place, Wilkinson said.

"It's so much less expensive to prevent than it is to eradicate, and when you get into, say, an aquatic system, eradication sometimes becomes impossible," he said.

Changing Habits, Not Habitats

Local, state and federal laws outline how fish can be transported and placed in the open water, but they're difficult to enforce if officials do not see the crime occur and if citizens don't know the laws exist, according to Wilkinson.

Last year, several government agencies, including the NOAA and the U.S. Fish and Wildlife Service, teamed up with the Pet Industry Joint Advisory Council to launch Habitattitude, an advertising and marketing campaign to raise public awareness of what to do if an aquarium pet outgrows its welcome.

"The pet industry doesn't want to be the cause of invasive species or people not handling species correctly," Wilkinson said.

The program has distributed specially marked bags to 700 pet stores, letting consumers know what to do when they want to get rid of a fish. Many shops will take back fish that have outgrown their tanks and replace them with smaller ones.

But the new U.S. lionfish colony — spawned by aquarium dumps — shows how the careless disposal of fish has already changed the nation's fresh- and saltwater systems.

"It will be interesting in the coming years to see if marine systems are going to be subjected to the same pressure from non-native plants and animals as freshwater systems have been in the past," said Schofield, the U.S. Geological Survey ecologist. "I don't know the answer to that."

The Final Fish Tale

One thing is certain: Catching a dumped pacu guarantees an angler instant notoriety.

Clements said his phone rang off the hook for weeks from locals wanting to see his fish with teeth that looked like "a set of dentures in its mouth."

Tourtillott made showing off the pacu a full-time job for a week. He kept it in a minnow tank at the bait shop.

"I showed it to people so many times that I think it finally died of shock," he said.

Tourtillott decided not to mount it because he figures someone in the area will one day catch another.

Clements plans to display his ferocious find in an alcohol-filled jar. He's enjoyed the piranha-vs.-pacu debate, but wonders if another might be lurking in his boyhood fishing hole.

"Can you imagine if somebody put two or three of those in the lake and they got together?" he said. "We'd have a lot of fish like this running around."