CLEARWATER, Fla. (WFLA) — The Clearwater Marine Aquarium announced Tuesday the “sudden passing” of resident rough-toothed dolphin, Rex.

In a series of tweets, the aquarium said, “It was our privilege to care for Rex, he was loved by our CMA family and guests from around the world.”

Rex was introduced to the aquarium in 2020 after rescuers determined he had significant hearing loss, making him non-releasable to the wild.

“For several years his health remained stable, but last week animal care staff noticed a change in Rex’s behavior, including his decline in eating,” the aquarium said in another tweet. “When his condition worsened, animal care staff intervened to monitor him 24 hours a day and provide Rex care to keep him comfortable.”

Despite their efforts, Rex passed away on Monday, March 6. A necropsy, similar to an autopsy for humans, is scheduled to determine Rex’s cause of death.

“The knowledge, research, and lessons Rex taught us will help us care for his species in the future,” CMA added.