It might give the impression of being a tardy little fellow, but then, all of a sudden… it turns out to be hardy.

The sarcastic fringehead (Neoclinus blanchardi) has a rather curious name, with an attitude to match. This creepy little fish can scare off animals much larger than itself with one show of its distended mouth, which is wider than its head, or even its whole body, for that matter.

Discovered in 1858, this ultra-aggressive little guy grows only to about 30 centimetres (12 inches) in length with a long and slender body, large pectoral fins and much smaller pelvic fins. It lives in the pacific waters, off the coast of North America – from San Francisco, USA to Baja California in Mexico.

Sarcastic fringeheads are ambush predators, which means they tend to stake out a hidey hole that offers them both protection and a vantage point from where to pounce on prey. Once they’ve reverse parked into their chosen nook, they’ll aggressively charge at anything that comes too near – including divers. And according to the survivors, they don’t like to let go.

Indeed, these fish are known for being big fighters. When two fringeheads battle for territory, they press their swollen mouths together, giving the impression that they are kissing – but in fact, they are actually determining who the larger fish is. The larger fish – or, more precisely, the fish with the larger jaw – wins dominance, meaning it bags the best den and a chance to mate.

Then, the female lays thousands of eggs in the prized location and the male fertilizes them. He then defends his offspring with yet more oral aggro.

Marine biologist Watcharapong Hongjamrassilp’s thesis research suggests that fringeheads use the different vivid colors on their mouths to communicate with each other. But then, they don’t look like they’ve got many nice things to say.

Image credit: Richard Herrmann

As for that peculiar name: ‘fringehead’ refers to the floppy fronds of tissue falling over the fish’s eyes, while ‘sarcastic’ is thought to either denote the animal’s sardonic closed-mouth expression, or derive from the Greek word sarkázein, which means ‘to tear flesh’.

And well, either of them could be true – just look at this.