The world’s oldest-known living aquarium fish, the aptly named Methuselah, is even older than previously thought, her age just having been recalculated up from 84 to 92. That puts the female Australian lungfish as starting life in 1931, when Jacques Cousteau was just coming of age.
The “cutting-edge” DNA analysis used to age the fish is believed by scientists Dr Ben Mayne of Australia’s Commonwealth Scientific & Industrial Research Organisation (CSIRO) and Dr David T Roberts of Australian government agency Seqwater to have advanced the accuracy of such calculations, and could also make it easier to work out the age of fish in the wild.
“Methuselah’s age was challenging to calculate, as it is beyond the currently calibrated clock,” says Dr Roberts. “This means her actual age could conceivably be over 100, placing her in the rare club of fish centenarians.”
The lungfish has been kept at San Francisco’s Steinhart Aquarium, part of the California Academy of Sciences (CAS), since before World War Two. She has doubled in size since arriving by liner in November 1938 with several hundred other fish from Fiji and Australia, all long since departed.
“Although we know Methuselah came to us in the late 1930s, there was no method for determining her age at that time, so it’s incredibly exciting to get science-based information on her actual age,” says aquarium projects curator Charles Delbeek.
“Methuselah is an important ambassador for her species, helping to educate and stoke curiosity in visitors from all over the world. But her impact goes beyond delighting guests at the aquarium – making our living collection available to researchers across the world helps further our understanding of biodiversity and what species need to survive and thrive.”
Steinhart Aquarium, which celebrates its own 100th anniversary this month, says that the analysis is part of a larger study designed to inform lungfish conservation efforts in the wild. It involved sampling 33 living lungfish from seven US and Australian institutions.
Australian lungfish can breathe using a single lung and live in slow-moving parts of rivers. A specimen known as Granddad at a Chicago aquarium was claimed to be more than 80 years old when euthanised in 2017.
In the past the challenging task of estimating a fish’s age relied on invasive methods such as examining earbones and removing scales, but the new method uses a tiny fin-clipped tissue sample said not to affect the fish.
“For the first time since the Australian lungfish’s discovery in 1870, the DNA age clock we developed offers the ability to predict the maximum age of the species,” said Dr Mayne.
“Accurately knowing the ages of fish in a population, including the maximum age, is vital for their management. This tells us just how long a species can survive and reproduce in the wild, which is critical for modelling population viability and reproductive potential for a species.”