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Hagfish Survive Attacks With Loose Skin and Lots of Slime

A new study looks at how the fish evade shark bites and fill predators' jaws with goo.

Attacking Shark Gagged by Slime

What does it take to survive on Earth for 300 million years?

The secret might just be the ability to ooze slime from your pores. The defense tactic has worked for the hagfish, an eel-like animal that looks like an oversized tapeworm. (Exactly how to classify the hagfish—also called slime eels—is debated among scientists, who see it as either a vertebrate or invertebrate.)

When a predator chomps down on the creature, it releases slime made of mucus proteins that expand when mixed with saltwater. The slime sets quickly, often choking whatever unlucky predator has grasped a hagfish. In case slime doesn't do the trick, hagfish also have a nightmarish four rows of large, jagged teeth, which they can use to take a bite out of attackers.

In 2011, researchers discovered just how effective this defense technique is thanks to underwater cameras. Dropping a camera to the sea floor with enticing sacks of bait, they illuminated the surroundings with a non-intrusive blue light. Using this technique, they were able to see how all the predators that zeroed in on hagfish were deterred.

In a paper on the experiment published in the journal Scientific Reports, researchers found that hagfish were also more active predators than previously assumed. Before the report, hagfish had only been observed burrowing into corpses to feast on the remains and were more widely seen as scavengers. (Read more about hagfish.)

Video footage from the 2011 experiment was so revealing that a group of scientists from the University of Guelph in Ontario used it to study how hagfish were evading predators' bites in the first place.

The fish's slime technique, after all, is only effective if the animal can survive the initial first bite from a shark or other large fish. The team theorized that hagfish either had puncture-resistant skin or skin that hung in such a way that it was difficult for predators to grasp.

Publishing their findings in the Journal of The Royal Society Interface Wednesday, scientists found that hagfish don't have puncture-resistant skin. Instead, it's loose and flaccid, meaning it's difficult for predators to penetrate internal organs. This loose skin also helps hagfish tie themselves in knots or burrow when they're hunting.

Watch: 'Slime Eels' Explode on Highway After Bizarre Traffic Accident

But once a predator comes into contact with hagfish skin, it triggers a stress response that releases slime in large volumes.

Last July, this stress response was responsible for one of Oregon's worst traffic jams. A truck carrying several thousand hagfish was headed from fisheries to a port, where the fish are sent to Asia to be sold for food. When the truck crashed, thousands of fish released their slime, cementing cars to the highway.

A small bulldozer was required to clean the road.