World's Oldest Fish: At Shedd Aquarium, 'Granddad,' Lungfish Is Euthanized Because Of Old Age

Granddad, presumed to be the world's oldest fish, passed away Sunday at the Shedd Aquarium in Chicago. The aquarium president announced Monday that the decision to euthanize the pre-historic Australian lungfish for humane reasons arose when he started to show signs of "shutting down," aquarium collections manager Michelle Sattler told the Chicago Tribune.

"For a fish who spent much of his time imitating a fallen log, he sparked curiosity, excitement and wonder among guests of all ages," Shedd Aquarium's CEO Bridget Coughlin said in a statement Monday, breaking the news. "(They) would hear his story and learn about the incredible biology that makes his species a living fossil and one of the oldest living vertebrate genera on the planet."

Granddad was already a teen when he was brought from Australia to the Shedd Aquarium in 1933 with his mate for the World's Fair, three years after its opening. Approximately 104 million aquarium visitors saw the 24-pound lungfish over the years. He was likely to have been in his mid-90s or older at the time of his death.

“It’s a sad week for us, and it’s history for a lot of people,” Collections manager of Granddad's care provider, Michelle Sattler said.

Spotted, four-feet long and able to breathe in and out of water, Granddad was loved by the zookeepers, who claimed he was "animated for a very-slow moving fish." Sattler told the Chicagoist that the lungfish "lived a pretty relaxed life, enjoyed interactions with us, including gentle pats along his back, and loved to eat his leafy greens."

Granddad was one of three other Australian lungfish who are exhibited at the aquarium, one of which is an African lungfish who is scheduled to go on display soon.

It was reported that the elderly lungfish lost interest in his food and had organ failure, a side effect to age-related complications, according to the Chicago Tribune.