Now DNA tests have revealed the age and birthplace of the world's oldest aquarium fish.
A fishy tale
The Australian Lungfish (Neoceratodus forsteri) lives in freshwater and can breathe air using its single lung. It was described as a species in 1870 and attracted huge international interest as a kind of living fossil.
We now know the Australian Lungfish is the closest living relative to all land-dwelling tetrapods. This is the group of four-limbed animals that includes everything from frogs to humans and dinosaurs to whales. The extinct ancestors of whales lived on land and had four legs. Believe it or not, snakes are also tetrapods!
Today, the Australian Lungfish is an endangered species and lives in just three river catchments in south-eastern Queensland.
Granddad's story began in one of these rivers. But mystery surrounds exactly where and when he was caught.
In 1933, at his full adult size of 109 centimetres but still a youngster, Granddad and a second Australian Lungfish made the 20-day voyage from Australia to the Chicago World’s Fair. Granddad lived at the John G. Shedd Aquarium in Chicago for 84 years. More than 100 million people visited him before his death in 2017.
DNA tests for discovering the ages of fishes
Demographic information, including the ages of individual animals in a population, is important for managing endangered species, like Australian lungfish. It's also hugely valuable to the fishing industry for managing stocks of harvested species.
"Our DNA tests for ageing use a tiny sample, such as a clip from a fish's fin. We extract DNA and look at epigenetic changes that have accumulated during the fish’s lifetime. It’s like looking at a clock and reading their age," Ben said.
“We’re interested in aquarium fish because they reveal the upper limits of a species’ lifespan. The known ages of fish that have been cared for in aquaria also help us to calibrate our clocks."
How old was Granddad Lungfish?
When Granddad died in 2017, staff at the John G. Shedd Aquarium preserved a small fin clip in ethanol. They provided it to the team for this research.
"Using DNA from this clip and our epigenetic clock, we calculated Granddad’s age at death. We also used genotyping to find out which population of Australian Lungfish he belonged to," Ben said.
The results revealed Granddad was born in the Burnett River, and he lived to the incredible age of 109.
According to the AnAge online database, only 11 other fish species live longer than the Australian Lungfish. All, but one of them, are temperate, deep water, marine dwellers.
Tom Espinoza, at Queensland Government, said this means Granddad not only holds the title of the oldest known Australian Lungfish to date.
"Granddad was likely the oldest freshwater sub-tropical fish in the world too," Tom said.
David Roberts, Senior Research Scientist at Seqwater, said the team is continuing to work on conservation of the species.
"Our next steps are to source additional samples from wild-caught Australian Lungfish, and from aquariums around the world, to further our understanding of longevity for the species," David said.
The paper, entitled Tell us a story Granddad: Age and origin of an iconic Australian lungfish, was a collaboration between CSIRO, Seqwater and the Queensland Government. It was published in Frontiers in Environmental Science.