Meet the Bony-Eared Assfish

The type of eel-like fish, which recently went on display in Canada, is a fascinating denizen of the deep sea.

With a name like assfish, you're probably used to being the butt of jokes, not a top news item.

After seeing a number of stories pop up about a funky little fish newly displayed at the Royal BC Museum in Victoria, British Columbia, Canada, I decided to take the author’s prerogative to ask “What in the world is a bony-eared assfish?”

The Royal B.C. Museum recently put this bony-eared assfish, discovered in Queen Charlotte Sound in 2006, on display. [Photograph By Royal Bc Museum]

It's actually a type of cusk-eel, an eel-like fish that resembles a "glorified tadpole, with a bulbous head and a tapering tail,” Gavin Hanke, curator of vertebrate zoology at the Royal BC Museum in Victoria, British Columbia, says via email.

The museum’s specimen was caught ten years ago in Queen Charlotte Sound (map), off the coast of central British Columbia.

Put on display at the museum in January, the odd-looking fish has been a delight to kids “who now have a valid excuse to say 'assfish,'” Hanke quips.

Are You For Eel?
Like many other deep-sea creatures, assfish bodies are “soft and flabby, and their skeleton is light and reduced,” says Hanke. A lack of food and high pressure at depth may make generating muscle and bone difficult.

It’s also chilly down there in the sunless depths—about 37 to 39 degrees Fahrenheit (3 to 4 degrees Celsius), so it’s likely assfish have slow metabolism that prevents them from being too active.

It "can move fast in short bursts," he adds, but the video "shows it to be a lazy swimmer, only fluttering its fins to make any headway."

Given that they're cold-loving creatures, assfish may also live in more northern oceans, though they haven't yet been discovered there, Hanke says.

The assfish is actually a type of tadpole-shaped fish called a "cusk-eel." [Photograph By Royal BC Museum]

Adam Summers, associate director at the Friday Harbor Labs at the University of Washington, notes that assfish live "pretty nearly everywhere it gets deep enough. That is a lot of oceanic territory to span."

Even so, finding an assfish in Queen Charlotte Sound is unusual—it's the only recorded specimen found there so far.

What’s In a Name?
In 1887, German ichthyologist Albert Günther bestowed the species with its scientific name, Acanthonus armatus, which may offer a clue to how its common name of bony-eared assfish came about.

Armatus, which means "armed" in Latin, was likely chosen because the fish sports spines off the tip of the nose and the gills. This also perhaps accounts for the “bony-eared” bit, according to Hanke.

Akanthos is Greek for “prickly,” and onus could either mean “hake, a relative of cod,” Hanke says, “or a donkey.”

Summers concurs, saying onus could easily read “as a homonym of the Greek word for ass.”

So perhaps the unknown scientists who “made up the common name just played with the donkey side of the etymology, and it stuck,” Hanke says.

On the subject of weird animal names, Hanke suggests checking out the common name for Halichoeres bivittatus: slippery dick. "It's amazing that this hasn't caught on in social media—assfish is tame by comparison."

Assfish Abound
Kids will love the fact that three other fish species have a nom de donkey: the Galathea assfish, the abyssal assfish, and the robust assfish.

None are in the genus Acanthonus, though, and Hanke says he’s has “no idea why” they, too, got labeled assfish.

Maybe they’re just jerks.

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