Viper Dogfish Profile
The deep ocean is home to some of the strangest-looking animals ever discovered. But that’s probably what they would say about us, too.
The further we get from familiar ecological conditions, the more animals diverge from familiar morphological adaptations, and while, often, there are some recognisable features among these creatures, they’re so warped and different, that it’s easy to imagine they come from an entirely alien lineage.
The viper dogfish is a great example of this. It has the rough shape of a shark, but the face that only Sigourney Weaver could love.
Viper Dogfish Facts Overview
| Habitat: | Marine, benthic/deep water |
| Location: | Northwestern Pacific Ocean |
| Lifespan: | Unknown |
| Size: | 54 cm (22 in) long |
| Weight: | Up to 0.76 kg (1.7 lb) |
| Colour: | Black |
| Diet: | Lanternfishes, crustaceans |
| Predators: | Unknown |
| Top Speed: | Unknown |
| No. of Species: | 1 |
| Conservation Status: | Least Concern (IUCN) |
The viper dogfish is not a viper, nor is it a dogfish. But it’s closely related to the latter, in a family of glowing sharks that aren’t all that well understood.
It spends much, but not all, of its time lurking in the depths – not only because it’s ugly, but because that’s where it has perfected its craft.
Its craft being lunging at bony fishes with a terrifying face, hidden in the dim light by its own luminous glow.
Interesting Viper Dogfish Facts
1. They’re not quite dogfish
The viper dogfish is named wrong three twice. There are no viper species that live in the sea – all sea snakes are elapids. And dogfish are members of the Squalidae family, which the viper dogfish isn’t.
Instead, they come from the family of lantern sharks, the Etmopteridae, which are named for the glowing organs found on their bodies. There are five genera in this family (Etmopterus being the best-known), and the viper dogfish makes up the smallest, as the only member of its genus: Trigonognathus.
But they’re not far from dogfish, and share the Squaliformes order with dogfish and five other families.
2. They’re mysterious
Being the only member of their genus may prove to be either a product or a cause of the lack of information about this species.
If they are indeed alone in the genus, we might struggle to learn more about them because of that, but it’s just as likely they’re not, and we just haven’t figured it out yet.
Either way, information on this species is thin in the water, as they prefer to stay hidden in the dark.
Being small, they evade many fishing nets, which is great for them but makes studying them harder. None have ever been successfully kept alive after being caught, and there don’t seem to be any cases of this species being studied in situ, so corpses are all we’ve got to go on.
They are perhaps ram feeders, hunting by rushing rapidly into something with their mouths open much like you see in an American all-you-can-eat buffet.
It’s thought they come up to around 200 metres during the day and descend to well below 400m at night, but they’ve only been found in waters off the coast of Japan, Taiwan and Hawaii, meaning there’s still a lot of the puzzle missing. 1
3. They’re deep-water sharks
Some individuals have been caught as deep as 1500 metres, which tracks with the distinctly alien look of this fish and the fact that it makes its own light.
Deep sea animals like this probably use photophores not as a way of illuminating themselves against their background, but as a way of disguising themselves against it.
The photic layer of the ocean goes to about 200 m deep. This is the point beyond which there isn’t enough light to photosynthesise, so this is where most of your photosynthetic organisms will be found.
Beyond 200 metres is the twilight zone, which has a little light, but far too little to trigger photosynthesis. Animals here may have huge eyes and use light to find mates or attract prey.
This goes down to about a kilometre, after which we enter the midnight, or aphotic zone, where no surface light can reach.
Still, there is light here – a general background hum created by the bioluminescence of other animals. This means that creatures trying to stay visually hidden, even in the midnight zone, need to match that background light with their own so as not to cast a shadow.
Having glowing cells along its belly, the viper dogfish is probably best suited for the twilight zone, where most of the dim light is coming from above. But you only have to look at them to know they’re from the deep. 2 3
4. They look the part
Even with their mouths closed, these fish have worse dentition than the British upper class. Their overlapping teeth stick out from their jaws, which extend in front of them from beneath a rubbery, elongated snout.
These are black, eel-like sharks with huge, reflective eyes and leathery skin and look right at home among the alien weirdos of the deep sea.
In their defence, all of the pictures of these sharks are of ones who are no longer with us, and (without fact-checking this) it’s safe to say that none of us looks all that hot when we’re dead.
5. They’re specialised
But all of this ugliness is there for a reason. Those enormous teeth are an obvious specialist tool for grabbing food, rather than cutting it, and this differentiates the lantern fish from a lot of the dogfish, who tear off chunks of flesh.
The extendable jaw is a great ambush predator adaptation, and coupled with the teeth works to latch onto and retrieve prey, which is then swallowed whole. This method allows the fish to catch and eat animals as much as 40% of their size and also gives legitimacy to the viper part of the nickname.
The huge eyes are highly reflective for picking up light (and shadow) in the depths, and then, of course, we have their own lights.
6. They glow in the dark
All members of this family have light-emitting organs along their bodies. In fact, it’s thought that this is the key adaptation that led the Squaliformes to radiate into the deep sea, around 120 million years ago.
While counter-illumination is the commonest use for these organs among the Squaliformes, the viper dogfish and its family have more complex photophores than many, leading researchers to hypothesise deeper uses.
Models suggest that they can also be used in communication between members of the same species, perhaps as species recognition or even something more detailed than this. 4
Viper Dogfish Fact-File Summary
Scientific Classification
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Order: | Squaliformes |
| Family: | Etmopteridae |
| Genus: | Trigonognathus |
| Species | kabeyai |
Fact Sources & References
- Sarah Gibbens (2018), “’Alien’-Like Sharks With Extendable Jaws Pulled From Deep Sea”, National Georgraphic.
- “Viper Dogfish”, IUCN Red List.
- Julien M. Claes (2014), “Photon Hunting in the Twilight Zone: Visual Features of Mesopelagic Bioluminescent Sharks”, Plos One.
- Julien M Claes (2015), “The presence of lateral photophores correlates with increased speciation in deep-sea bioluminescent sharks”, NIH.