National Geographic

Hagfish filmed choking sharks with slime, and actively hunting fish

The hagfish looks like an easy meal. Its sinuous, eel-like body has no obvious defences, but any predator that moves in for a bite is in for a nasty surprise. The hagfish releases a quick-setting slime that clogs up the predator’s gills, causing it to gag, choke and flee. Scientists have known about this repulsive defence for decades, but Vincent Zintzen has finally filmed it in the wild. His videos also prove that hagfish, generally thought to be scavengers of the abyss, are also active hunters that can drag tiny fish from their burrows.

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.

You can see the results below. 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.

The slime could also give the hagfish a competitive edge among other scavengers. If many hagfish were feeding off Zintzen’s bait, it soon became draped in slime. The mucus puts off fish competitors, allowing the hagfish to monopolise their morsels.

Zintzen also filmed some hagfish hunting, a behaviour that had been suspected but never witnessed. While they’re typically regarded as scavengers, some scientists have suggested that their numbers are so great that they couldn’t possibly be sustained by corpses alone. On top of that, some people have found the flesh of prawns, worms and fish among the stomach contents of hagfish.

Zintzen filmed slender hagfish chasing after red bandfish, ensconced in sandy burrows. The hagfish completely ignored the bait that Zintzen was offering. Instead, they seemed to search the ocean floor for hidden burrows, using the whisker-like barbels on their faces. Once they found an entrance, they rapidly burrowed inside, emerging several minutes later.

“When I first reviewed this video, I thought: those hagfish are not very clever. They have the bait right above their head and they keep on searching the sediment for it.” Then, Zintzen noticed one particular hagfish that had stuck the front third of its body inside a hole. It twisted its body into a knot, using it for leverage to push against the sediment. Twenty seconds later, it withdrew from the burrow with a red bandfish, dead and motionless, in its mouth. “I then only understood what was actually happening: they were hunting!”

Hagfish are well known for their ability to tie themselves in knots, which can travel down the length of their bodies. This could help to clear their own bodies of slime (they can choke on their own mucus) or free themselves from the grip of a predator. Here, the knot seemed to give the hagfish leverage for pulling the bandfish from its burrow. Zintzen thinks that the hagfish may even have used its mucus as an offensive weapon, to choke the bandfish inside its burrow.

Hagfish have been swimming in the oceans for 300 million years, and there are 77 species spread all over the world. While the jawed fishes have undoubtedly taken over the seas, the hagfishes have clung on. They have a defence that makes them all but untouchable. Their only predators are either very large fish whose gills are too big to clog, or mammals, which don’t have gills and whose stomachs can easily digest or expel the slime. They also have a versatile style of feeding that includes scavenging, opportunistic feeding and active hunting.

“They are fantastic animals, but most probably, you need to be a scientist (and a somewhat strange one) to state this and love them,” writes Zintzen.

PS It’s sad that this paper didn’t come out on October 16th, which was designated as Hagfish Day.

Reference: Zintzen, Roberts, Anderson, Stewart, Struthers & Harvey. 2011. Hagfish predatory behaviour and slime defence mechanism. Scientific Reports. http://dx.doi.org/10.1038/srep00131

Images and videos by Zintzen et al.

More on hagfish: When diving into food, why not absorb it through your skin?

There are 9 Comments. Add Yours.

  1. 2buns
    October 27, 2011

    Thought the hagfish day was the 19th of Oct.
    Enjoyed reading this!~

  2. Jim
    October 27, 2011

    Well, I’m not a scientist, just a science bug, and I think they’re pretty awesome.

    That said, I’m not especially keen on touching them or anything. I did that once and, well, they aren’t kidding about the mucus production thing. It’s pretty intense.

    Neat story, Ed!

  3. Lam Son
    October 27, 2011

    It seems to be working because most fishes don’t only bite : they open their mouth quicky to suck water and prey into their mouth before biting. In the case of hagfish, they suck the slime as well.

  4. Bogleech
    October 27, 2011

    They are absolutely beautiful to watch in motion.

  5. Hisham
    October 28, 2011

    lol.. I feel that someone spits in your moth a very thick throat discharge, I will never want to be a fish hehehe

  6. Jonathan
    October 28, 2011

    So if some form of man made slime the next miracle shark repellant?

  7. tom
    October 29, 2011

    Hagfish, you can’t reason with them, you can’t bargain with them, they have no mercy or remorse and they absolutely will not stop until you are covered in their slime!

  8. Rosemary
    October 30, 2011

    This is amazing! If I only had one for a pet, then I could get my little brother to stop bothering me!

    I celebrated Hagfish Day with my class…so this was cool to see!

  9. Katie
    September 26, 2012

    This article and the videos are wonderful!!!! I love hagfish and always explain the fantastic quality about how they are living fossils to kids!!!!

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