They’re not even supposed to be here. But lionfish -– those beautiful but poisonous fish, native to the Pacific and Indian oceans – are spreading rapidly along the south Atlantic Coast, are actively breeding, and are here for good, scientists reported today.

In a new study, the National Oceanic and Atmospheric Administration says the accidental introduction of lionfish to the Atlantic in the early 1990s has become irreversible, and represents a wild card for the already stressed-out marine ecosystems from Florida to Cape Hatteras, N.C.

Agency experts also want ocean divers, offshore fishermen and coastal doctors to be on the alert for the whiskered, brownish tropical fish – and to the nasty stings that can result from even touching one of their many, flowing venomous spines.

“There is potential that this species could become a serious invader,” Dean Wilkinson , NOAA’s director of invasive species, said during a conference call Thursday with reporters.

Three years ago , NOAA announced 14 lionfish sightings off the East Coast, from New York to Georgia, with 11 around shipwrecks off North Carolina. On Thursday, the agency reported that deep-water sightings have quadrupled since then, that breeding grounds have tripled in number, and that the coastal population now is about 1,000.

“Removing lionfish from the southeast United States continental shelf ecosystem would be expensive and likely impossible,” wrote Jonathan A. Hare and Paula E. Whitfield , the authors of the report. The two NOAA researchers are based at a marine lab in Beaufort, N.C., and ask anyone who catches or witnesses a lionfish to call them, at 252-728-8714.

With red, maroon and white stripes, lionfish are attractive and popular additions to aquariums, growing to about 17 inches long.

They require warm waters to live and typically have been seen near the Gulf Stream, where depths reach more than 120 feet . They have no known predators in the Atlantic, and eat smaller fish, shrimp and crabs.

Spines along their fins and back inject venom into prey – or into the hand of a curious human. Their sting has never been known to kill a person, but the puncture causes much pain and swelling and requires quick medical attention, scientists said. No one has been stung yet on the Atlantic coast, but a fisherman reeled in a lionfish near Morehead City , N.C., in March.

This summer, Whitfield will lead a first-ever field study of Atlantic lionfish, to be launched from Wilmington, N.C., out to waters of depths between 120 feet and 170 feet.

The three-week investigation will be a fact-finding mission of sorts, as scientists know little of how lionfish live, reproduce and feed in the Atlantic.

Ultimately, NOAA hopes to generate enough know-how to craft a strategy for controlling, or at least managing, the exotic invaders.

The first known release of lionfish in the Atlantic occurred after Hurricane Andrew struck south Florida in 1992. During the mammoth storm, a home aquarium near Biscayne Bay was shattered, allowing a lionfish to escape into coastal waters.

Scientists said they are not seeking a ban on lionfish for aquariums, nor are they putting a bounty on the fish. By contrast, Virginia officials set a bounty for another invasive species, the veined rapa whelk , which turned up in the lower Chesapeake Bay. And several states, including Virginia and Maryland, have banned the import of snakehead fish because of their potential to escape into waters and wreak havoc on smaller species.

Lionfish are not expected to move into Virginia waters because the average temperature is too cold. Cape Hatteras is thought to be the northern limit for lionfish.