A lungfish believed to have been the longest-living aquarium fish has been put down due to failing health.

The Shedd Aquarium in Chicago said the fish, in his 90s, was euthanised after losing interest in food and showing signs of organ failure.

Granddad, who weighed 11kg (24lbs), had been seen by more than 100 million people since arriving in Chicago from his native Australia in 1933.

Image: Granddad, the world's oldest aquarium fish. Pic: Shedd Aquarium/Brenna Hernandez

He was believed to be in his teens at the time, meaning he could have been in his 90s or possibly beyond the century mark.

A Shedd spokeswoman admitted Granddad's exact age was unknown, but that he was believed to be in his mid-90s.


Image: Lungfish are a protected species in Australia. Pic: Shedd Aquarium/Brenna Hernandez

Lungfish, which can live to be more than 100 years old and are a protected species in Australia, have existed for nearly 400 million years and fossils show they have remained unchanged for more than 100 million years.

They are native to two rivers in Queensland, have a single primitive lung and are among the few fish that can breathe air.

Shedd Aquarium president Bridget Coughlin announced his death: "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 and one of the oldest living vertebrate genera on the planet."