(Photo courtesy of R. Babb - Arizona Game and Fish Department)

Gila Chub.

Three types of chub in the Colorado River watershed may actually be the same species of fish. The finding raises questions about their protections under the federal Endangered Species Act.

The U.S. Fish and Wildlife Service proposed listing the headwater chub and roundtail chub as "threatened" last year.

A third fish — the Gila chub — is already listed as endangered.

But experts at the American Fisheries Society said it’s not possible to tell the three fish apart.  

“Their finding is that they’re all of the same species and therefore we can’t list them individually under the Endangered Species Act as separate species,” said Steve Spangle, Fish and Wildlife Service supervisor.

INTERACTIVE: See A Timeline Of Arizona's Threatened And Endangered Species

Spangle said the agency must reconsider the proposed listing and may have to take another look at the Gila chub’s endangered status.

It’s unclear if the new ‘combined’ species would qualify for federal protection, because its population is larger and therefore more resilient to threats.

The agency is asking for public comments. It will make a decision on the species status by April.

Comments can be submitted to the Fish and Wildlife Service until 10 p.m. local time on Friday.