(CNN) -- A 12-year-old male killer whale, who showed signs of being ill only the day before, died Tuesday afternoon at SeaWorld in San Diego, California, the park announced.
The cause of death for Sumar won't be known until a necropsy is complete, SeaWorld said. Results may not be known for several weeks.
"It's a very sad day," spokesman Dave Koontz told CNN. "He was a great young killer whale. He was sharp."
Sumar, who weighed about 5,000 pounds, had been at SeaWorld San Diego since 2001, coming from an Ohio park. He was one of seven killer whales at SeaWorld and was able to exhibit about 100 "behaviors," Koontz said.
The killer whale had no medical history or problems with behavior, the spokesman said, adding that there was no evidence of communicable disease. "He had a great disposition."
"Trainers had noticed that Sumar was acting lethargic yesterday (Monday) afternoon. Park veterinarians began a regimen of antibiotics to help try to stabilize his condition while they attempted to determine the cause of his illness," a SeaWorld statement said.
"His condition worsened today and a decision was made to cancel the 12:30 p.m. Shamu show, so that trainers and veterinarians could continue to devote their full attention to Sumar. Despite these efforts, Sumar did not survive."
Sumar's trainers and support staff were devastated by the sudden loss and are sharing stories, Koontz said. "The loss of any animal is difficult, but that was even more so."
Orlando, Florida-based SeaWorld was recently fined $75,000 by the Occupational Safety and Health Administration for three safety violations, including one classified as willful, after an animal trainer was killed by a whale in Orlando in February. SeaWorld, which also has a location in San Antonio, Texas, said it would contest the violations.
The last killer whale to die at the San Diego venue was Splash, who was sickly when SeaWorld adopted him. He was nursed back to health and lived 15 years until 2005.
No public memorial for Sumar is planned, although fans will be able to comment on the park's Facebook page, Koontz said.
SeaWorld said its shows would resume on schedule Wednesday.