Story highlights Australian lungfish 'Granddad' passes away

Fish, the last living link with the aquarium's earliest history, was estimated to be around 100 years old

(CNN) He was the one that didn't get away -- eventually living for around a century.

Chicago's Shedd Aquarium has announced the passing of their oldest-living resident, an Australian lungfish named Granddad.

At least he didn't meet his end in fishy circumstances -- the Shedd website released a statement online that said that, "after a rapid decline in his health" its animal care team had made the "difficult decision to euthanize" the fish.

The aquarium estimates that he'd made it to 100 and while it could never be completely sure how old the old-timer was, he was in his teens when he was transferred to the aquarium in 1933. In 2013, Granddad celebrated his 80th anniversary at Shedd.

Granddad, and a fellow lungfish -- his mate, who died in 1980 and was also on display at Shedd -- were the first of their kind to be featured in an American aquarium.

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