The fish is estimated to be more than 90 years old, but was euthanised on Sunday after it started showing signs of organ failure and had stopped eating.
"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.
According to a Shedd Aquarium spokesperson, Granddad, the world's oldest lungfish, has passed away, leaving behind a lot of memories and broken hearts.
Grandad was seen by more than 104 million guests during his time at the aquarium and although his exact age is unknown, Australian lungfish can reach age 100 and the team "think he was close to it". He has been the star attraction of the Chicago-based aquarium since 1933 when he was brought all the way from the Sydney Aquarium in Australia.
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The fish had been at Chicago's iconic aquarium since the Century of Progress World's Fair in 1933.
Lungfish, which have existed for more than 380 million years, are among a few fish species that can breathe air and live to be 100 years old. It would also seem that Granddad managed to outlive most of his caretakers, and, up to this day, no one knows for certain the lungfish's age.
"He loved to eat his leafy greens", offered Granddad's primary handler Michelle Sattler in a statement. "During his almost two-year hiatus in a reserve area, staff members repeatedly assured anxious aquarium members and other guests that their favorite lungfish was doing fine and would be back on view in a spacious new habitat recreating a Queensland riverbank ecosystem". At a party marking his 80 anniversary at the museum, the Australian consul general presented the aquarium with a certificate that states, "Granddad exemplifies the tremendous relationship between the John G. Shedd Aquarium and the Government of Australia".
Granddad appears to have been a firm favorite for numerous aquarium's visitors.