Marineland, however, offers a different take.
"As you have probably seen from many of the tabloid magazines, you see in grocery store lineups, anyone can take an unflattering photo of someone to make them look unwell or unhappy," the park noted in a statement to The Dodo.
Marineland also said Zeus gets regular checkups from an on-site medical team as well as independent veterinarians.
"Activists will continue to post misleading information and photos of all of our animals," Marineland adds. "We will continue to provide accurate information and care for all of our animals."
But few at the park have known Zeus as long, or as intimately, as Demers. He worked with the park's walruses for 12 years before quitting in 2012. Zeus' condition, he says, led to a "heated argument" with his employer and, ultimately, his resignation.
"I've seen him collapse many times," he recalls. "He would delay shows. He has a chronic regurgitation issue."