Hagfish helped by its slime


This video is about a hagfish surviving predators’ attacks because of its slime.

From New Scientist:

Imagine you’re a humble little red bandfish. To keep away from predators you hide in a burrow on the sea floor, occasionally poking your head out to see if it’s safe to leave. It’s not an exciting life, but you’re doing OK.

Then one day, minding your own business, you suddenly find yourself drenched in sticky mucus. You can’t breathe, because it has clogged your gills.

Your enemy is a hagfish. After you’re dead it will drag you out of your burrow and devour you. But it’s unlikely anyone will try to devour it in turn, because that slime it used to kill you also protects it from predators. Besides, why would anyone want to eat a creature that regularly eats decaying corpses from the inside out?

On the prowl

Hagfish are partway between fish and worms, with a spinal cord but no backbone. In this sense they resemble the common ancestor of all backboned animals, and have changed little in at least 300 million years.

Long thought to be scavengers, they have now been seen actively hunting for the first time. Vincent Zintzen of the Museum of New Zealand in Wellington and colleagues used underwater video cameras to catch them in the act. In December 2009 they saw a hagfish belonging to the genus Neomyxine go on the attack. …

Shark repellent

Zintzen’s cameras caught only one species of hagfish in the act of hunting, but it may be that they all do it. They can produce lots of slime quickly, which would certainly come in handy.

Hagfish also use their slime to get rid of predators. Zintzen filmed 14 cases of larger fish biting a hagfish only to get a mouthful of slime and beat a hasty retreat. The unlucky predators convulsed their gills to clear them of slime, like a human gagging. Even formidable predators like kitefin sharks were held off (see video, above).

That’s impressive, because kitefins panic many fish. Zintzen’s colleague Andrew Stewart once saw a group of spiny dogfish become so desperate to escape a kitefin that – counterproductively – they jumped out of their tank. In the observations made in the wild, the hagfish did nothing of the sort, and were remarkably blasé about predators. They ignored them unless they were bitten, and even if they were attacked they didn’t appear to suffer injuries, and carried on feeding as if nothing had happened.

Feasting on decay

Hagfish also get food by scavenging. When they come across a big carcass, they burrow into it and then eat it from the inside. Uniquely for a vertebrate, as well as having a gut, they can absorb nutrients through their skin and gills.

That’s all very well, but feeding inside a decaying corpse has its own problems, says Chris Glover of the University of Canterbury in Christchurch, New Zealand. There will be little oxygen in the water, and lots of toxic ammonia from the rotting flesh. But it seems the hagfish can cope with that too.

Glover captured Pacific hagfish (Eptatretus stoutii) off the coast of Vancouver, Canada, and studied how they responded to high ammonia and low oxygen. Many animals stop taking in nutrients under such conditions, because doing so uses up the scant oxygen and they must devote energy to battling the toxic effects of the ammonia.

Not the hagfish. Ammonia had no effect on their food uptake, and low-oxygen water actually increased it. Faced with hypoxia, the hagfish tripled the amount of the amino acid glycine that they took in through their gills, and absorbed six times as much through their guts. Much of this glycine ended up in their brains, possibly protecting neurons from damage.

This ability to shrug off oxygen deprivation and ammonia poisoning may have served the hagfish well over the years. “Without this tolerance, it might be less competitive for the limited food resources available to an animal that scavenges,” Glover says. What’s more, oxygen levels in the sea do crash sometimes, but hagfish seem happy in their low-oxygen hell.

Journal references: hagfish hunting video, Scientific Reports, DOI: 10.1038/srep00131; ammonia and anoxia, Physiological and Biochemical Zoology, DOI: 10.1086/662630

See also here. And here.

Hagfish slime as a model for tomorrow’s natural fabrics: here.

The Hagfish’s Special Trick for Warding Off Predators: Thick, Sticky Mucus: here.

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