World's oldest aquarium fish, Methuselah, older than originally believed and still charming visitors at SF Steinhart Aquarium

Ever wonder where is the world's oldest living fish being housed in an aquarium? It happens to be in San Francisco, according to the California Academy of Sciences (Cal Academy).

Methuselah, an Australian lungfish (Neoceratodus forsteri) at Cal Academy's Steinhart Aquarium, is 92 years old, according to a DNA analysis by Dr. Ben Mayne of the Commonwealth Scientific and Industrial Research Organisation and Dr. David Roberts of Seqwater.

The beloved fish, with an upper age estimate of 101, was previously believed to be 84 years old, Cal Academy biologists said in a news release this week.

Methuselah has been in Steinhart Aquarium since November 1938, outliving more than 200 other fishes from Australia and Fiji that arrived in the public aquarium with it.

"She has become famous not only for her advanced age, but for her charming personality and penchant for belly rubs," Cal Academy biologists said.

Methuselah could also be celebrating her centennial this year along with Steinhart Aquarium due to the fish's upper age estimate, they said.

"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," said Charles Delbeek, curator of aquarium projects at Steinhart Aquarium. "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."

According to Cal Academy, Methuselah's age was determined by Drs. Mayne and Roberts in a study that sampled 30 other lungfish from six other institutions across the U.S. and Australia to create a catalog of living lungfish that will advance the accuracy of the previously developed DNA-based age clock for the species.

The study included a new "harmless" method that uses a tiny tissue sample from a fin clip less than 0.5 square centimeters, Cal Academy biologists said.

"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," Dr. Mayne said.

"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 modeling population viability and reproductive potential for a species. It is a rare and valuable opportunity for researchers to access exceptionally long-lived fish such as Methuselah kept in the care of California Academy of Sciences, as it helps us understand maximum longevity of a species under ideal care conditions.

While the fish's age prediction will improve over time, it will always "live beyond the calibrated age clock, as no other lungfish we know is older than Methuselah," according to Dr. Roberts.

"This research highlights the important and often serendipitous discoveries that can occur from working with public aquariums and institutions that maintain protected species in their care. This approach to researching longevity of rare and endangered animals could be extrapolated to almost any vertebrate species, and demonstrates the value that animal care institutions such as the California Academy of Sciences can play in advancing animal knowledge to improve conservation management of species in the wild," he said.

The two biologists plan to publish their full study findings later this year.