Monday, 6 February 2017

Deep Sea Dragonfish

Image: Fran Martín de la Sierra
My name is Deep Sea Dragonfish, eater of worlds.
Look on my face, ye Mighty, and despair!

No argument here!

Image: NOAA
Deep Sea Dragonfish, also known as Barbeled Dragonfish, are a family of fish found in oceans all over the world. There are almost 300 species, some of them extremely long and thin, others only longish and rather pudgy. Some species are widespread throughout tropical and temperate waters, others come from chilly, Antarctic waters.

Not that they experience a great deal of warmth wherever in the world they reside. These guys, like Marine Hatchetfish and Deep Sea Anglers, are poster-children for the deep sea!

Image: Fran Martín de la Sierra
A Viperfish
Teeth. It's all about the teeth. Teeth for miles. Teeth for days. Teeth so long they seem to deform the entire head to fit themselves in. Fangs that spill from the mouth like a snake wearing three pairs of unnecessary dentures. Or, perhaps, a perfectly ordinary dragon. But their scientific name doesn't refer to their teeth. It refers to their mouths.

Deep Sea Dragonfish belong to the family Stomiidae, which means mouth. There are 28 genera within it, and a lot of them have extremely cool names.

Image: Julian Finn / Museum Victoria
You know how in fantasy worlds you sometimes have all those fire dragons, ice dragons, stone, wood and chaos dragons? Well, with Deep Sea Dragonfish you have the same thing, but with mouths. For example, there's Pachystomias (thick mouth), Leptostomias (thin or delicate mouth), Odontostomias (tooth mouth. Sort of goes without saying, doesn't it?), Flagellostomias (scourge mouth), Eustomias (good mouth) and, my favourite, Aristostomias (best mouth).

I am Aristostomias, dragon elite, aristocrat of mouths!

Image: Kenaley, Christopher
Longbarb Scaly Dragonfish (Stomias longibarbatus), a Scaly Dragonfish
Oh, and don't forget the genus Stomias (mouth). Pure and simple.

There's even one called Astronesthes. The common name gives a pretty good impression of the meaning: Stareater. Wow. Turns out 'eater of worlds' was just the beginning! Although, in the interest of keeping things in proportion, it should be pointed out that the longest Deep Sea Dragonfishes are about 50 cm (20 in) long. So... Star-nibbler, I guess?

Image: President and Fellows of Harvard College
Threadfin Dragonfish (Echiostoma barbatum), a Scaleless Black Dragonfish
Like any poster-child for the abyss, Deep Sea Dragonfish are also bioluminescent. They typically have a barbel, what you might call a "dangly bit on their chin", with a little, light-up blob on the end. They also have rows of bioluminescent spots on their sides as well as a few more patches here and there.

Deep Sea Dragonfish are ambush predators who lurk in the shadows and use their glow-in-the-dark barbels to lure fish to their teeth. Since they're deep sea fish, they live in what is essentially one, gigantic, globe-spanning shadow. That means they can drift about, conserve their energy, and wait for something tasty to arrive.


Having said that, they're not actually quite that lazy. Many fish, Deep Sea Dragonfish included, undergo vertical migration. Every night, they swim up to shallower, plankton rich waters to feed. Some deep sea fish do it to eat the plankton. Deep Sea Dragonfish do it to eat the fish that eat the plankton. Then, as morning comes, they descend back to the depths.

Sounds like a long way for a midnight snack! No wonder then that your typical Deep Sea Dragonfish likes to hunt (or bump into) big game. They won't turn their nose up at a tiddler, but they also need to be prepared to cram in something that probably ought not fit. That's why they're committed to opening their mouths very, very wide. Like 120 degrees wide. They can open their mouths to an obtuse angle!


The way they do it is by getting rid of some of their neck bones. That's usually a Bad Idea. Most vertebrates like to keep their heads firmly attached to their necks. This is considered a Good Idea. But Deep Sea Dragonfish have incredibly flexible necks by virtue of lacking some of the vertebrae right behind the skull. The only thing keeping their head on is a flexible notochord. All vertebrates have a notochord running down their back, it's just they usually have a backbone to go along with it.

With this flexible neck, Deep Sea Dragonfish can lift their upper jaw up almost as much as they can lower their lower jaw down. Now they can eat... too much. Or just enough. When you're a fish who can't be sure where your next meal is coming from, and you eat everything WHOLE, you need to be ready to eat something approximately the same size as you are.

Image: Kenaley, Christopher
Smalltooth Dragonfish (Pachystomias microdon), a Scaleless Black Dragonfish
But Stomiidae is a fairly big family with a lot of fish. They don't even all have big teeth. For example, remember Pachystomias (thick mouth)? That genus contains only one species: P. microdon. The Smalltooth Dragonfish.

The Stomiidae family can be split into 6 subfamilies.

Image: President and Fellows of Harvard College
Astronesthes haplophos, a Snaggletooth
Snaggletooths (Astronesthinae).

This is the subfamily that has the Stareaters. They're probably not what comes to mind when people think 'Dragonfish'. They all seem to be a bit on the pudgy side and the biggest one is only 30 cm (12 in) long. They're also scaleless.

Image: Kenaley, Christopher
Malacosteus niger, a Loosejaw. They probably look like this when they yawn
Loosejaws (Malacosteinae).

Again, not your typical Dragonfish but these guys are really cool! These guys definitely lack those neck bones so they can open their jaws ridiculously wide. They also lack a floor on their lower jaw. Not only does this give them a charming, skeletal quality, it also means they can shoot their mouth quickly without getting slowed down by drag. The biggest species only reach about 24 cm (10 in) long.


Video: EVNautilus
A Viperfish

Viperfish (Chauliodontinae).

This is more like it! These guys can reach 30 cm (a foot) long and they're very thin and armed with wicked fangs for catching prey. They're not 'Barbeled', though. Nothing on the old chinny-chin-chin. They have an extremely long, dorsal fin spine, instead.

Image: President and Fellows of Harvard College
Eustomias monodactylusa Scaleless Black Dragonfish
Finally, the real deal. The most Dragonfishy of all the Dragonfish.
Scaly Dragonfishes (Stomiinae) and Scaleless Black Dragonfishes (Melanostomiinae), both up to 40 cm (16 in) long.
And Black Dragonfishes (Idiacanthinae), which reach up to 50 cm (20 in) long

These guys are long, slim, fanged, and have glowing barbels dangling from their chin. All these Dragonfish still have all those other patches of luminescence, too. The ones on their underside might be used to hide their silhouette when they swim closer to the surface. Others might be used to attract the opposite sex.

Image: President and Fellows of Harvard College
Larvae can have guts longer than the rest of their body
Not a lot is known about Dragonfish reproduction. At least some of them lay eggs that float to the surface so the larvae can feed on tiny plankton, like copepods and the like. They might even be eating the exact same plankton that attracts all those deep sea fish at night. In the interests of absorbing every bit of nourishment from every meal, they have what's known as 'trailing guts.'

It sounds like a terrible complication after a surgical procedure but really it means that the larva has part of its guts trailing out from its belly. Which is just as bad. Sometimes there's more guts than fish! I guess it's one way of keeping trim. Pile up all your intestines in a wheelbarrow beside you. Human intestines are like 25 feet long. Think of all the things you could do while using the toilet! Actually don't.

Image: Carl Chun
Larval Idiacanthus fasciola
Finally, special mention has to go to Black Dragonfishes in the genus Idiacanthus. They grab themselves a few more Deep Sea Weird Points by having males one sixth the size of females and growing from the weirdest larvae, ever. They call it the 'Stylophthalmine trait.' In other words, eyes on stalks! Long stalks. Uncomfortably long stalks. Now they can see everything, particularly predators and prey.

And who knows? Perhaps some of those predators are exactly the kind of fish they'll grow up to eat?

Scary stuff in the deep sea. You never know when dinner might grow up to be a dragon.

6 comments:

Potato Potato said...

Love your blog, I'm glad to see it's still active after I read the article created for the Darwin's Bark Spider.

Joseph Jameson-Gould said...

Thank you!

Keith M said...

That stalk-eyed larva is one of the weirdest creatures I have ever seen. I love it.

Also, I was wondering: have you considered putting a random article button on the site? I usually just can't decide what weird animal I want to read about and would love to see ones I wouldn't have previously!

Joseph Jameson-Gould said...

Hmmmm... A random button sounds like a good idea, I'll look into it. Thanks for the suggestion!

Tim said...

One thing is for certain, those dragonfish larvae have guts! I suppose it takes guts to be a dragonfish larvae though. Up there floating about peacefully eating plankton when it could be mom or dad coming up from from the depths to eat you! Yeah, that would take guts.

Joseph Jameson-Gould said...

They have guts and they're not afraid to show it! They SHOULD be afraid to show it, but I guess they act like they have teeth before they get the teeth.

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