Scientists believe newly discovered demon cavefish may be among the rarest fish in the world

Bobcat Cave near Huntsville is home to the endangered Alabama cave shrimp, two species of cave crayfish and the southern cavefish. Those were all Dr. Matthew Niemiller expected to find when he set out to survey the cave system last year.

Instead, he discovered a bizarre-looking fish, previously unknown to science. Niemiller said he believes this fish may be among the rarest in the world.

The newfound species is eyeless and features a hunchback, spiny rays and a snout shape unlike that of other cavefish species. What’s more, the fish completely lacks pigment; beneath its translucent skin, you can see its brain.

This transparency isn’t that uncommon, said Dr. Jonathan Armbruster, curator of fishes at the Auburn University Museum of Natural History in Auburn, Alabama, and a coauthor of a recent study on the discovery.

“You usually see it in the smaller fishes, things that live in open water,” Armbruster said. “They’ll often have a clear body so that they can be cryptic in the clear waters.”

The creature resembles the stuff of sci-fi dramas — and, fittingly, it has been dubbed Demogorgonichthys arcanus, or demon cavefish, a name derived from the monster Demogorgon in the Netflix TV series “Stranger Things.”

Initially, Niemiller, the new study’s lead author, was uncertain whether the fish belonged to a previously discovered species: the southern cavefish.

“Over the years, I’ve seen how variable cavefish can be, and I’ve been fooled before by animals that looked different but were genetically very similar,” said Niemiller, an associate professor of biological sciences at the University of Alabama in Huntsville. “But this one was different in ways that kept holding up.”

Niemiller shared photos of the fish with Armbruster and Dr. Pamela Hart, an assistant professor of biology at the University of Alabama who is also a coauthor of the study.

Upon comparing the specimens with the southern cavefish, Armbruster said he started noticing the differences. The team performed CT scans, genetic tests and other analysis on the fish and discovered that these bizarre-looking creatures were skeletally different from other already identified animals in the cave.

Based on these results, the researchers described the fish as a newly identified genus and species.

It’s unclear how many demon cavefish exist, but they may be among the rarest fish in the world, Niemiller said. “The species is known from a single site based on our best knowledge with presumably a very small population size,” Niemiller wrote in a text message.