Mystic Aquarium says Kodiak,  its 15-year-old Stellar sea lion, was euthanized Friday.  Aquarium officials say Kodiak, who arrived from the Vancouver Aquarium ten years ago, did not respond to treatment of liver disease and kidney failure.

The aquarium says the one-ton sea lion was a favorite among visitors,  and impressed trainers with his intelligence.

A necropsy is planned,  in hopes of learning more about his illness.