Hagfishes, an ancient group of eel-like animals found on the bottom of the ocean, release a nasty slime when bitten by a predator fish. The slime sends the predator into fit as it “coughs” up the substance, trying to prevent suffocation, which usually leaves enough time for the slime eel to escape.
But dramatic escape aside, how can hagfishes survive that initial bite?
Researchers from the University of Washington, Chapman University and University of Guelph have published new research showing how hagfishes survive an initial attack from predators before they release large volumes of slime to defend themselves. Results show that hagfish skin is not puncture resistant; instead, it is both unattached and flaccid, which helps avoid internal damage from penetrating teeth.
Their study published this week in the Journal of the Royal Society Interface.
This short video shows how hagfishes use slime as their defense mechanism. Additional footage of attacks, lab studies of how their defensive slime functions and the fact hagfishes are rarely found in the stomachs of other fish suggest that fish predators are rarely successful when they attempt to eat a hagfish.
“This video really was the inspiration for our entire study,” said Douglas Fudge, associate professor of biological sciences at Chapman University and lead author on this study. “A sizable slack volume in hagfishes, combined with minimal attachment of the skin to the muscle, allows the body to slip out of harm’s way even when the skin is punctured.”
Researchers studied the three layers of hagfish skin to determine how they survive the initial attack. They narrowed it down to two possibilities — the hagfishes have either puncture-resistant skin or a loose and flaccid body design that makes it more difficult for teeth to penetrate. The performance of hagfish skin is notable because they lack scales that help boost puncture resistance in many fishes.
Students at the UW’s Friday Harbor Laboratories tested the fish skin as part of a 2014 summer course taught by Adam Summers, a professor of aquatic and fishery sciences and of biology. They performed skin puncture tests of 22 fish species including hagfish.
“We tested a wide range of fish skin because we were convinced that hagfish skin, which makes excellent leather, would be far harder to penetrate,” Summers explained. “It was a surprise that it was as easy to poke a hole in hagfish skin as flounder skin, but the hagfish skin is so loose it just slides away rather than getting cut.”
Hagfishes have a subcutaneous sinus system that runs the length of their body, containing 30 percent of their blood volume. Although previous research has found evidence that this sinus system is crucial to burrowing and knot-tying, this study shows that it also plays a role in predator defense.
Source: University of Washington