Black Scabbardfish Profile
Black Scabbardfish was the obscure band Edward Teach started that was so ahead of its time, that nobody liked it, which would ultimately push him to piracy.
It would one day be plagiarised by some factory workers from Birmingham and end up making them quite rich.
But it’s also the name of a deep-sea eel-like fish that is, paradoxically, a cutlassfish.
Black Scabbardfish Facts Overview
| Habitat: | Deep marine |
| Location: | North Atlantic: Denmark to the Western Sahara |
| Lifespan: | Unknown, 14 to 32 across varying estimates |
| Size: | Up to 1.5 m cm (5 ft) |
| Weight: | Up to 4.2 kg (9.3 lb) |
| Colour: | Black |
| Diet: | Crustaceans, cephalopods, fishes |
| Predators: | Larger fishes, humans |
| Top Speed: | Fast |
| No. of Species: | 1 |
| Conservation Status: | Least Concern |
Black scabbardfish aren’t all that well known, on account of them sort of exploding when brought to the surface.
These slender deep-sea fish are sought after by fisheries for their flavour but also harbour dangerous amounts of heavy metals that could be enough to kill a person if they eat the wrong bit.
They appear to grow quite fast as juveniles, in the relatively hostile mesopelagic ocean, before slowing down significantly and sinking into the murky depths to lead life as a scary black spike in the dark.
Interesting Black Scabbardfish Facts
1. They’re Cutlassfish
Usually, cutlasses are presented inside scabbards, but in this instance, it’s the other way around.
The cutlassfishes are around 45 species of deep and nasty predators from the dark ocean, known for being slender and quick with big teeth. They’re in the tuna order, which contains some of the most muscular and dense fish predators there are.
This scabbardfish is one of about four species in its genus, and sports enormous teeth and eyes that are large enough to be useful at depth.
2. They’re deep-sea fish
Not all scabbardfish are black, which is why this one gets the name. They’re not all deep-sea animals, either, but if it’s hard to remember, their common names tend to be quite descriptive.
There’s the silver scabbardfish, the intermediate scabbardfish, the doubtful scabbardfish and then Sleepy, Happy, Bashful and Doc.
Anyway, this one is black. And it’s a deeper water than, for example, the silver scabbard fish, found at depths of up to 1,700 metres.
Down here, they’re a top predator.
3. They’re fast
These are long and narrow fish with pointed, spear-like heads full of gnarly, fang-like teeth and large eyes. This tells you a lot about an animal and it’s all bad news.
There’s no light from the surface at these depths but there is light – it comes from any number of bioluminescent organisms that glow in the dark, creating a faint background hum for the eyes – enough to silhouette a tasty morsel against if you have big enough peepers.
The iridescence on the scabbardfish helps it blend into the almost-black, and from this position of advantage, the fish feeds on almost anything it can get its jaws around. Pretty metal.1
4. Black Sabbathfish
There are very few vegetables in the ocean, which leads its inhabitants to form more carnivorous diets. Almost everything in the ocean is therefore an eater of animals, which is starkly different than on the land.
But the issue with this is the way various compounds work their way up the food chain. On land, you might have a chain with very few links: grass – sheep – human – crocodile. Or, soy – cow – human again. Or, if you’re really efficient: Soy – human.
Essentially, the more chains you have, the more crap you’ll have in your food.
In the ocean, these links can be several times as many. Phytoplankton are the producers of the ocean and these are eaten by zooplankton, which can be eaten by krill, which can be eaten by small fish, who are then eaten by very slightly bigger fish. Then, at the top, there are monsters like the tuna, great white and Cthulhu.
Each of these stages eats more than one of its predecessors and when those predecessors are swimming around in dissolved toxic waste from volcanoes and industrial plants, their predators start collecting heavy metals in their tissues.
Different heavy metals form reservoirs in different animal communities and generalist predators consume the lot. Then, specialist predators consume the generalists, and it concentrates up the food web in a process called biomagnification.
These heavy metals are surely very bad for the ocean inhabitants, but they have been there for half a billion years, so they do have a pretty strong tolerance to them when compared with us.
This means they can accumulate to a degree that is far beyond the lethal limit for humans. Humans, who then go into the ocean and grab the fish to eat.
In the black scabbardfish, they accumulate in the liver, which, consequently, the WHO recommends you don’t eat; lethal quantities of lead, mercury, and cadmium await those who dare. The rest of the fish’s meat is highly prized, which might be causing the species some issues. 2
5. Ear crystals
There’s a trend among the kind of people who think crystals are magic to throw around a lot of words like “balance” and “perception” into concepts they can’t really define because they don’t exist. But ear crystals are a bit of an exception.
Otoliths, or “ear stones” are suspended calcium deposits in the ear of vertebrates that aid with balance and perception of acceleration. These “ear crystals” are often responsible for debilitating vertigo as they can come loose and send the wrong signals to the brain about which way is up.
In a rare case of actual treatment sounding like mindless quackery, the alignment of the ear crystals can bring back balance.
But they can also be used to age a fish.
Because, as fish grow, these stones grow layers of crystals around them, like the rings of a tree, at more or less a regular rate. Smashing the head of the fish to release its precious crystals can therefore tell you how old it was before you smashed its head.
6. They’re fast-growing, then slow-growing
The deep-sea adults of this species don’t begin life on the sea bed.
They start off as naïve and optimistic little mesopelagic larvae growing rapidly into juveniles, floating around in the relatively shallow depths of around 200-400 metres and believing in their hearts that they can be the ones to break the cycle.
Juveniles aren’t well understood on account of them not making a lot of sense, and not being caught by fishing vessels all that much.
As a result, their lifecycle isn’t fully described, but at some point, the young scabbardfish’s hopes are dashed and it sinks unenthusiastically to the ocean floor to live life in a more or less identical way to its parents.
Down here they age more slowly, moping around, day after day for what’s thought to be the 14 years of their lifespans.
Unfortunately, this slow growth is a problem for the species when pesky ships keep putting them out of their misery before they can pass it on to their offspring.
So far, they’re of least concern but thought to be vulnerable to overfishing based on their perceived rate of recovery. 3
Black Scabbardfish Fact-File Summary
Scientific Classification
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Scombriformes |
| Family: | Trichiuridae |
| Genus: | Aphanopus |
| Species: | carbo |
Fact Sources & References
- “Black Scabbardfish”, IUCN Red List.
- Nadhirah B. Saidon (2024), “Trophic transfer and biomagnification potential of environmental contaminants (heavy metals) in aquatic ecosystems”, Science Direct.
- Beatriz Morales-Nin (1996), “Age and growth of the black scabbard fish (Aphanopus carbo) off Madeira”, Science Direct.