SF’s Oldest Aquarium Fish Has Such a Cool Evolutionary History

The 90-plus-year-old lungfish that calls San Francisco home loves bivalves, figs… and, yes, belly rubs.

Zoological facilities offer people the rare chance to see some of the world’s most unique, oftentimes at-risk, wildlife. Large exhibits that feature charismatic mammals— reticulated giraffes, African elephants, jaguars, great apes, cetaceans (though this, thankfully, is changing), etc. — are usually the fauna we synonymize with these wildlife parks. However… what if I were to tell you that San Francisco’s own California Academy of Sciences houses not only the oldest aquarium fish in the city but likely the entire country?

Meet Methuselah: the 90-plus-year-old Australian lungfish that came into San Francisco on a steamship from Queensland, Australia back in 1938.

Nearly a year ago, the San Francisco Chronicle published a glorious profile on the magnetic fish that does, in fact, use both its primitive lungs and gills to sequester oxygen. (As the newspaper noted, the name “Methuselah” is a Biblical nod to Noah’s grandfather, who lived to 969 years old; the fish is now almost 4 feet long and weighs around 40 pounds, and will likely still keep growing [as most fish do the rest of their lives; they’re what we call animals without “predetermined growth” in biology]; she likes fruit snacks and belly rubs.)

And what is just as captivating about Methuselah’s own San Francisco story is the evolutionary biology of the species she, herself, is a part of.

Australian lungfish—also referred to as “Queensland lungfish,” due to their naturally occurring distribution inside slow-flowing pools and river systems found around south-eastern Queensland—are among the oldest-living fish species known to science, with some examples, like Methuselah, living 90 or more years. It’s believed the longest-lived Australian lungfish must be a centenarian. (Screw our blue zones, am I right?)

They, too, are among just one of six living extant lungfish species left in the world and are the only surviving member of the genus Neoceratodontidae. Four species in the genus Protopterus (animals under the family Protopteridae) are found in Africa; one species, Lepidosiren paradoxa (the sole species in the family Lepidosirenidae) is found in South America; the Australian lungfish is the only species in the family Ceratodontidae — and is also among the stockiest-built of all the known lungfish.

How did these fish procure their primitive lung systems, which are nearly identical in both function and structure to that of amphibians? They got rid of their swimming bladders, which is why lungfish have pectoral and pelvic fins, as well as a single unpaired caudal fin replacing the dorsal, that look slightly dextrous and mirror rudimentary limbs.

Because, yes: Lungfish are just as good at walking through marshy wetlands as they are gliding through the shallow, slow-moving water habitats they’re found in.

It’s not exactly understood just how old the species is, itself. However, fossil records of examples in this group have been carbon-dated as far back 380 million years, around the time when the higher vertebrate classes began emerging on the planet — a full 170 million years before the first mammals are believed to have roamed. Moreover, fossils of lungfish have nearly identical anatomies to those found today, suggesting that they’ve existed largely unchanged for well over 100 million years.

Lungfish aren’t just primitive; they’re among the oldest living vertebrates on this space rock.

But because humans are assholes, many of the still-living lungfish species, including the Australian lungfish, are “threatened,” per reports from the International Union for Conservation of Nature (IUCN). Some are even “endangered” according to the IUCN, like the Australian lungfish. All of them currently face human-facilitated habitat loss and mounding threats to their riparian environments due to the climate crisis.

Next time you’re looking for a rainy day activity, go pay Methuselah a visit. And beseech to whichever higher power you choose to honor that human greed doesn’t rob future generations of the chance to see members of her species fawn over tummy pats.

Feature image: Courtesy of Twitter via [at]mythosamante

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