Back when I worked at a public aquarium, one of my favorite fish for the sheer cool factor was the Pacific hagfish, Eptatretus stoutii. So ugly that only a mother (or an aquarist) could love them, hagfish have the added disadvantage of being carrion eaters, which means that anyone not turned off by their looks is usually turned off by their diet. Not only do they eat dead stuff, but they crawl inside the carcass and eat it from the inside out. (Better protection that way.)
And if all that doesn’t make you squicky, there’s the slime. Hagfish produce a mucus which absorbs vast amounts of seawater, expanding mightily in the process. The result is slippery, tough, and astonishing in its volume. Fishermen hate seeing hagfish in their nets due to the sheer mess. It has long been thought that this slime was a defense measure, making hagfish unpalatable to larger fish that might otherwise see them as a meal. In 2006, a researcher named Jeanette Lim showed that the slime can clog the gills of predators — even better than just tasting bad — but nobody had ever seen this defense used in the wild.
Now fish researcher Vincent Zintzen has filmed it. The result is featured on Not Exactly Rocket Science, and you should go take a look.
The hagfish in the videos are attacked by sharks, conger eels, wreckfishes and more. In less than half a second, the predator’s mouth and gills are filled with slime. It leaves, gagging and convulsing, slime hanging in long wisps from its head. Even voracious seal sharks turn tail. The cameras didn’t follow the fleeing predators, so Zintzen doesn’t know if they eventually died or if the slime dissolved away. Either way, the hagfish, uninjured and oblivious, just carried on feeding. Its defence is so effective that it can totally ignore the fact that a shark just tried to bite it.
Quite by accident, Zintzen also filmed something else that had been suspected about hagfish but never proven: they’re not just carrion eaters. In fact they’re quite capable hunters, diving into the burrows of smaller fish and yanking them out — possibly after first suffocating them with slime.
Hunters who can’t be hunted? That’s a recipe for huge success in the survival game. It appears that the unattractive, primitive hagfish is just about the most impervious fish in the ocean. You don’t have to be pretty to win.