Hagfish are sometimes classed as fish although that’s in dispute, for they lack both backbones and jaws. Instead, their mouths contain a wide plate of cartilage, armed with two rows of horny teeth. It uses these to rasp away at carcasses that sink from above. Watch a dying whale settle on the ocean floor, and it will soon be covered in writhing hagfishes.
They are disgusting feeders. They burrow deep into corpses and eat their way out, and can even absorb nutrients through their skin. And if they’re threatened or provoked, they produce slime – lots of slime, oozing from the hundreds of pores that line their bodies. The slime consists of large mucus proteins called mucins, linked together by longer protein threads. When it mixes with seawater, it massively expands, becoming almost a thousand times more dilute than other animal mucus.
A single hagfish can clog a bucket of water within minutes, and in 2006, Jeanette Lim showed that the slime can equally clog the gills of predators. But until now, no one had ever seen the animals use this defence against an actual predator. They have mostly been filmed at whale carcasses with remote vehicles; their predators had a glut of whale meat at hand, and may have been put off by the noisy, bright vehicles. Instead, Zintzen filmed hagfish in more natural conditions, using a network of baited cameras. “Our units are not moving, producing minimum noise and using lights emitting only in the blue to avoid deterring the fauna,” he says.
As a student I remember catching some hagfish on a cruise in the Pacific. We put a couple of them in a five gallon bucket and stirred it. The hagfish filled the bucket with slime. It's a remarkable defense.
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