For such a tiny fish, the snail darter has haunted Tennessee. It was the endangered species that swam its way to the Supreme Court in a vitriolic battle during the 1970s that temporarily blocked the construction of a dam.
On Friday, a team of researchers argued that the fish was a phantom all along.
“There is, technically, no snail darter,” said Thomas Near, curator of ichthyology at the Yale Peabody Museum.
Dr. Near, also a professor who leads a fish biology lab at Yale, and his colleagues report in the journal Current Biology that the snail darter, Percina tanasi, is neither a distinct species nor a subspecies. Rather, it is an eastern population of Percina uranidea, known also as the stargazing darter, which is not considered endangered.
Dr. Near contends that early researchers “squinted their eyes a bit” when describing the fish, because it represented a way to fight the Tennessee Valley Authority’s plan to build the Tellico Dam on the Little Tennessee River, about 20 miles southwest of Knoxville.
“I feel it was the first and probably the most famous example of what I would call the ‘conservation species concept,’ where people are going to decide a species should be distinct because it will have a downstream conservation implication,” Dr. Near said.
The T.V.A. began building the Tellico Dam in 1967. Environmentalists, lawyers, farmers and the Cherokee, whose archaeological sites faced flooding, were eager to halt the project. In August 1973, they stumbled upon a solution.
David Etnier, a dam opponent and a zoologist at the University of Tennessee, went snorkeling with students in the Little Tennessee River at Coytee Spring, not far from Tellico. There, they found a fish on the river bottom that Dr. Etnier said he had never seen before, and he named it the snail darter.
The fish became a “David” to pit against “Goliath” — because if it were to be protected under the Endangered Species Act, the dam’s construction would be blocked.
“Here’s a little fish that might save your farm,” Dr. Etnier told a local farmer, according to the book “The Snail Darter and the Dam,” by Zygmunt Plater, an emeritus law professor at Boston College.
Elected officials were eager to finish the dam, and grew increasingly frustrated.
“This two-inch fish, which surely kept the lowest profile of all God’s creatures until a few years ago, has been the bane of my existence and the nemesis of what I fondly hoped would be my golden years,” Senator Howard H. Baker Jr. of Tennessee said about the snail darter in 1979.
That year, Representative John Duncan Sr., a Tennessee Republican, also described the snail darter as a “worthless, unsightly, minute, inedible minnow.”
After the Supreme Court upheld the protection of the snail darter, President Jimmy Carter signed a bill that exempted the Tellico Dam from the Endangered Species Act. The dam began operating in 1979.
Jeffrey Simmons, an author of the study who formerly worked as a biologist at the T.V.A., discovered what appeared to be snail darters in 2015 on the border of Alabama and Mississippi, far from the Tellico Dam.
“Holy crap, do you know what this is?” Mr. Simmons said to a colleague in the creek that day.
Mr. Simmons knew it shouldn’t be there if it were truly a snail darter.
Ava Ghezelayagh, now at the University of Chicago, and colleagues conducted analysis of the fish’s DNA and compared snail darter physical traits with other fish. That led to confirmation that it was a match with the stargazing darter.
Dr. Plater, who also argued successfully for the fish in the Supreme Court case, took issue with the Yale study. He said the approach favored by Dr. Near and colleagues makes them genetic “lumpers” instead of “splitters,” meaning they reduce species instead of making more. He believes the findings also lean too heavily on genetics.
“Whether he intends it or not, lumping is a great way to cut back on the Endangered Species Act,” Dr. Plater said of Dr. Near.
Dr. Near said being described as a “lumper” was a pejorative in his world, and he added that most of the research he and colleagues had performed had resulted in speciation splits, including a 2022 study.
“The work strengthens the Endangered Species Act, because it shows how science can be revised with additional information and newer perspectives,” he said. “The methods we use in this study are leading to the discovery of scores of new species, many of which are more endangered.”
Decades after the Tellico Dam battle, the fish formerly known as the snail darter is thriving. It left the endangered species list in 2020.
“This is still a success story,” Mr. Simmons said. “Its listing under the Endangered Species Act worked, regardless of what you call this fish.”
While Mr. Duncan died in 1988, his son, former Representative John J. Duncan Jr., known as Jimmy, said his father would have felt vindicated.
“He felt the project should have never been stopped by that little snail darter,” he said.