CHICAGO — An Australian lungfish that entranced visitors to Chicago’s Shedd Aquarium for more than 80 years has been euthanized because of old age, the tourist attraction announced Monday.

Granddad, who was 4 feet long and weighed 25 pounds, had stopped eating and started showing signs of organ failure. He was euthanized Sunday. A necropsy – or animal autopsy – found conditions consistent with old age, aquarium officials said.

“For a fish who spent much of his time imitating a fallen log, he sparked curiosity, excitement and wonder among guests of all ages who would hear his story,” said Bridget C. Coughlin, Shedd Aquarium’s president and chief executive officer.

Shedd estimates Granddad was more than 90 years old.

The aquarium acquired him from the Sydney Aquarium in Australia during a 1933 collecting expedition and Granddad was one of two lungfish that attracted visitors during that year’s A Century of Progress International Exposition in Chicago. Aquarium officials estimate more than 104 million people saw Granddad over eight decades.

Rob Vernon, a spokesman for the Association of Zoos and Aquariums, said the nonprofit group is unaware of any older fish kept by a zoo or aquarium that it accredits in the U.S. or eight other countries.