Puffy the spotfin porcupinefish, a fan favorite at the Denver Zoo, has died unexpectedly, the zoo announced Wednesday.

Puffy has been a staple of the zoo’s Tropical Discovery exhibit since she came to the zoo in 2010 from a private dealer. While porcupinefish are not considered endangered, Puffy was the only fish of her kind at the zoo, officials said.

“(Puffy) delighted guests and keepers with her curious and sweet nature, and will be deeply missed by all,” the zoo said in a statement.

Zoo officials do not know what caused Puffy’s death. She was 12 to 14 years old and spotfin porcupinefish typically live up to 10 years in the wild, according to the Aquarium of the Pacific.

Puffy was described as beloved by all and “a great fish to work with” by Carlie McGuire, the zoo’s digital content manager.

“She was target trained, meaning we worked with her to get her to swim to a target so that she could eat her own diet away from the other fish in the tank,” McGuire said. “Target training is something we do with a lot of mammals so that they can participate in their own health care, but not as common for fish.”

Dozens of people took to social media Wednesday to share photos and stories of Puffy, saying she would greet zoo guests by pressing her mouth against the tank glass.

The zoo does not have any plans to get a new porcupinefish, officials said.