The Zuni bluehead sucker feeds on algae in flowing water, and has suffered from logging, grazing, loss of water and the use of chemicals used to help rainbow trout.

New Mexico Fish and Game Dept.

WASHINGTON — A fish found only in the Little Colorado River watershed in Arizona and New Mexico was declared an endangered species Thursday by the U.S. Fish and Wildlife Service.

The Zuni bluehead sucker was once prevalent in the watershed but has seen its numbers fall sharply, with conservationists saying it has been pushed to the brink of extinction.

“It is a tremendous relief for the fish to get the protection it needs,” said Michael Robinson of the Center for Biological Diversity, which petitioned Fish and Wildlife 10 years ago to protect the fish.

The listing does not officially take effect for a month, and the government must still rule on a proposal to declare 293 miles of stream as critical habitat for the fish. That decision is expected by the end of the year.

But Robinson said the center was “absolutely delighted and relieved” about Thursday’s announcement, which provides “muscular authorities that can now be exercised to prevent extinction.”

“It’s real,” Robinson said of the threat to the sucker. “This beautiful fish living in the high desert is under a tremendous amount of stress and threats.”

Those threats include loss of water — from drought and human activity — as well as logging and livestock grazing, according to the Fish and Wildlife listing.

In years past, the sucker was also threatened by the use of chemicals that were meant to remove green sunfish and fathead minnow so that rainbow trout could be introduced for sport fishing.

The Zuni bluehead sucker has a bluish head and a silvery-tan to dark green torpedo-shaped body. It typically does not exceed 8 inches in length.

The fish feeds on algae that it scrapes off of rocks and plants and requires clean, flowing water. Silt can smother their eggs.

Zuni bluehead suckers live in small, isolated and semi-isolated populations, which can lead to inbreeding and lower chances of survival.

The government estimates that the distribution of the suckers in New Mexico shrank by 95 percent over the last 30 years. The decrease in Arizona populations is unknown.

Fish and Wildlife is developing a recovery plan for the fish, but is already “actively protecting” it, said Melissa Mata, a service biologist.