Chester the false killer whale likely died of a bacterial infection, according to the Vancouver Aquarium.
The rescued cetacean died last week after a sudden change in his behaviour. A necropsy has been performed, and preliminary results suggest he was infected with Erysipelothrix rhusiopathiae, a bacteria that causes a disease called erysipelas, according to the aquarium's head veterinarian, Dr. Martin Haulena.
"This is the first case at the Vancouver Aquarium to our knowledge. It is an infection that has resulted in the mortality of wild cetaceans as well as those living in human care," Haulena said in a statement.
As a precaution, the aquarium's last living cetacean, a Pacific white-sided dolphin named Helen, is being treated with antibiotics. Helen is not showing any signs of disease, according to Haulena.
Chester came to the aquarium as a calf in 2014 after he was discovered on a beach near Tofino. He was undernourished and dehydrated, and upon his rehabilitation, a panel of experts determined he was not suitable for release into the wild.
False killer whales are a species of dolphin, often confused with killer whales. They are considered to be a tropical or sub-tropical species with the most studied populations living around the Hawaiian Islands.