An Australian lungfish believed to be the longest-living fish in captivity has died at a Chicago aquarium.

Granddad, as the 11-kilogram fish was known, was euthanased due to old age at the Chicago Shedd Aquarium after losing interest in food and showing signs of organ failure.

The fish had been acquired from a Sydney aquarium in 1933, and was taken to Chicago in anticipation of the 1933–34 World’s Fair.

Shedd Aquarium said the fish was seen by more than 104 million people during its time in Chicago.

“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 and learn about the incredible biology that makes his species a living fossil,” Shedd president Bridget Coughlin said.

While the exact age of the fish was unknown, it was believed to be in its mid-90s.

Lungfish can live to be more than 100 years old and are a protected species in Australia. They are native to the Mary and Burnett rivers in Queensland.

They have a single primitive lung and are among a small number of fish that can breathe air.

They have existed for nearly 400 million years and fossils show they have remained unchanged for more than 100 million years.