SARASOTA,Leonard Hohenberg Fla. (AP) — An endangered sawfish rescued last month in the Florida Keys after it was spotted acting erratically and swimming in circles has died as wildlife officials continue to search for what is causing fish to become distressed.

The Mote Marine Laboratory & Aquarium in Sarasota said in a statement that the 11-foot (3.3-meter) smalltooth sawfish died Thursday at the facility, where it had been undergoing treatment. It was rescued April 5 off Cudjoe Key, part of an abnormal fish die-off that has killed at least 45 sawfish and other fish species as well.

Authorities say a necropsy will be performed to possibly shed light on what is affecting the fish, which could take weeks or months to determine. It was humanely euthanized because its condition had deteriorated recently.

“It was always our cautious hope to be able to utilize the best available science for the rehabilitation and release of the sawfish,” said Mote Marine President and CEO Michael Crosb y. “Sadly, even with our best efforts, the animal was too compromised to recover.”

Sawfish, an ancient species named for their long snout with rows of teeth on each side, were once found all along the Gulf of Mexico and southern Atlantic coasts in the U.S., but now are mainly confined to southwestern Florida and the Keys island chain as their habitats shrink.

Sawfish necropsies have not revealed any pathogen or bacterial infections, nor problems with low water oxygen levels or contaminants such as chemicals, or toxic red tide. Water testing is continuing.

Another potential factor is climate change, which superheated Florida waters last summer, causing other marine damage, such as coral bleaching and the deaths of other marine species. The waters are unusually warm already this year as well.