The aptly named Methuselah, a lungfish at the Steinhart Aquarium in San Francisco, is the oldest fish held in captivity, with an estimated age between 92 and 101 years.
Methuselah arrived on US soil in 1938, on a steamboat from Australia, along with 230 other fish. Today, she – scientists believe it’s a female, although they can’t be sure – is the only living fish out of all the ones that left the steamboat. She was only a little fish back then, but she kept growing as the years passed and the aquarium life seemed to suit her.
The people peering at her through the glass wall didn’t seem to stress her out one bit, and she still enjoys peering back at visitors to this day. She was originally given the unofficial title of oldest fish in captivity back in 2017, when experts estimated her age at 84.
However, more recent tests showed that Methuselah is even older than previously anticipated – at least 92 years old and up to 101.
The lungfish are one of the most fascinating fish species on Earth, but also one of the toughest to properly date. That has a lot to do with how different the species is to most other types of fish. Scientists usually harvest the ear bones of fish after their death and count them like tree rings to estimate their age, but lungfish have very different ear bones. In fact, they are more closely related to humans or cows than to salmon or cod.
Lungfish can breathe air using a single lung when they are out of water or when the water composition changes, and they also happen to have the largest genome out of all known animals – 43 billion base pairs. That’s roughly 14 times the number of pairs in humans.
“Genetics is really quite straightforward for normal fish – but for lungfish, they’re so unique and so different that all of those techniques didn’t or don’t work,” David T Roberts, a senior scientist with Seqwater, told The Guardian. “It’s always pushed the envelope on uncovering some of its secrets to be able to manage and conserve it – and age is a really important one.”
Staff at the Steinhart Aquarium describe Methuselah as a happy, content fish, but scientists are curious to know if she actually feels or acts old, compared to younger fish. That’s tough to tell, but some experts believe geriatric fish do have some telltale signs – spinal changes, weight loss, cloudy eyes, and even a graying of the scales. However, none of these have been observed in Methuselah yet.
“We don’t know that that’s actually tied to her age,” the aquarium’s director said about Methuselah’s slight change in coloration over the years. “But it’s the only thing that we have seen physically that looks different for this fish.”
Methuselah and her species still hold plenty of secrets, but scientists are determined to uncover most of them. For now, we know that she is the oldest fish in captivity and that judging by how lively she looks, she may be holding onto the title for quite a while.