Deep-sea fish are some of the most interesting types of animals on the planet, and yet there isn’t really all that much known about many of them. And, for that matter, they haven’t really worked their way into the public imagination in the same way that most land animals, and large sea-surface-living species have. This article seeks to remedy that — detailing some of the most interesting species, as well as providing beautiful(!?) images of these species.

For more information and images, see: Deep Sea Animals & Life — Fundamental Patterns, Convergent Evolution, & Other Worlds

The black dragonfish (Idiacanthus atlanticus) is a very interesting, or perhaps strange, looking fish that lives deep in the ocean — in the mesopelagic and bathypelagic layers, around 5000-7000 feet deep.

Some of the more interesting things to note about the black dragonfish are: the very distinct looking, long fang-like teeth; the bioluminescence (including in infrared); the bizarre method of sexual reproduction; and the lure-based, ambush method of hunting. And, also, the reality that it looks almost exactly like the alien from the movie Alien.

The long-nosed chimaeras (Rhinochimaeridae) are a family of cartilaginous fish that possess a very distinct, long conically shaped snout. They don’t really look that much like anything else that I’ve seen before, and yet they still look kind of familiar? Almost like something you might see in a weird dream.

The snout in question is highly innervated, and functions as a means of finding food in the very dark environment of the deep, deep ocean. Interestingly, the rather pronounced first dorsal fin features a venomous spine that’s thought to be used in self-defense.

Long-nosed chimaeras are usually found in temperate and tropical seas, at depths of around 660 to 6,560 feet. Their range is spread out across the world, as is common with many families of deep-sea fish. They typically grow to be 3-5 feet in length.

The blobfish. What else is there to say?

Have you ever seen anything that looks like this before? In fairness, the blobfish (Psychrolutes marcidus) actually looks a bit different than these pictures when its in the highly pressurized deep-sea environment that it calls home. When brought to the surface though, the bodies tend to grossly deform.

They typically are found at depths of between 2,000 and 3,900 feet, where the pressure is considerably higher than it is at sea level — making gas-bladders largely inefficient for maintaining buoyancy. So, instead, the flesh of the blobfish “is primarily a gelatinous mass with a density slightly less than water; this allows the fish to float above the sea floor without expending energy on swimming. Its relative lack of muscle is not a disadvantage as it primarily swallows edible matter that floats in front of it such as deep-ocean crustaceans.”

The giant oarfish (Regalecus glesne) is a very, very big species of oarfish in the family Regalecidae. The species is the longest known bony fish in the world — regularly growing to be over 30 feet long.

The longest one on record was recorded as being 36 feet long, but much larger individuals have been reported before (56 feet long), they just haven’t been scientifically confirmed. The heaviest one on record weighed in at about 600 lbs, so they aren’t exactly light either.

Given the great size of the animal, and it’s shape, it’s been speculated that the fish may have inspired some of the sea-serpent legends common throughout many areas of the world. The species is oceanodromous, with a nearly worldwide distribution. It is thought to mostly inhabit the mesopelagic layer — ranging as deep as 3,300 feet.

There really isn’t that much known about the animal’s behavior — knowledge has mostly been limited to the occasional the dead or dying one washing up on shore. Though there is recent footage of a large one swimming in its natural environment in the mesopelagic — captured by an ROV.

The footage shows that the giant oarfish does indeed swim straight up-and-down while feeding — it’s quite interesting to watch something that big and ribbon-like swim like that.

Barreleye fish are a type of small deep-sea fish, comprising the family Opisthoproctidae. They are found in tropical-to-temperate waters, throughout the Atlantic, Pacific, and Indian Oceans.

Their name describes them pretty well — they possess barrel-shaped, tubular eyes, encased inside a transparent head. There’s not really anything like them. These eyes are generally directed straight upwards in order to detect the silhouettes of available prey.

More of the strangeness is detailed here: “The opisthoproctid eye has a large lens and a retina with an exceptionally high complement of rod cells and a high density of rhodopsin (the “visual purple” pigment); no cone cells are present. To better serve their vision, barreleyes have large, dome-shaped, transparent heads; this presumably allows the eyes to collect even more incident light and likely protects the sensitive eyes from the nematocyst (stinging cells) of the siphonophores from which the barreleye is believed to steal food. It may also serve as an accessory lens (modulated by intrinsic or peripheral muscles), or refracts light with an index very close to seawater. Dolichopteryx longipes is the only vertebrate known to use a mirror (as well as a lens) in its eyes for focusing images.”

A number of the species also possess “luminous organs” — owing to the presence of symbiotic bioluminescent bacteria (phosphoreum vibrionaceae). The light is focused downwards, and is thought to be something like a camouflage — so that when seen from below the silhouette isn’t too obvious.

Deep-sea hatchetfishes are small mesopelagic-living ray-finned fishes of the stomiiform subfamily Sternoptychinae. They aren’t closely related (at all) to the freshwater fishes commonly known as hatchetfishes — being from an entirely different family of fishes.

“Found in tropical and subtropical waters of the Atlantic, Pacific and Indian Oceans, marine hatchetfishes range in size from Polyipnus danae at 2.8 cm (1.1 in) to the 12 cm (4.7 in)-long Giant hatchetfish (Argyropelecus gigas). They are small deep-sea fishes which have evolved a peculiar body shape and like their relatives have bioluminescent photophores. The latter allow them to use counterillumination to escape predators that lurk in the depths: by matching the light intensity with the light penetrating the water from above, the fish does not appear darker if seen from below. They typically occur at a few hundred meters below the surface, but their entire depth range spans from 50 to 1,500 meters deep.”

The body, as you could probably guess, and can certainly tell from the photos, is shaped a lot like a hatchet. It’s not entirely clear what the reasons for the peculiar shape are.

Many of the species possess quite brilliant, almost mirror-like silver scales. They possess large tube-shaped eyes, that work excellently in very low-light conditions, and can focus on objects both near and far.

The Sloane’s viperfish (Chauliodus sloani) is a species of dragonfish from the genus Chauliodus,. It’s found in all of the world’s tropical and subtropical oceans — typically at depths of up to 2,500 meters.

The Sloane’s viperfish currently holds the record for the largest teeth relative to head size in a fish. The teeth are so large that the fish must open first “open its mouth to make the jaws vertical before it can swallow prey”.

When it wants to eat something particularly large, it can “lower the internal skeleton of the gills, allowing the prey to pass into the throat without interference.”

As you can no doubt guess, the large teeth are used to great effect in hunting — allowing for the complete impaling of prey fish. The species grows to be about a foot long.

The frilled shark (Chlamydoselachus anguineus) is one of only two remaining species in the ancient family Chlamydoselachidae. And has often been referred to as a “living fossil” thanks to its possession of a number of “primitive” features.

The species is found throughout a relatively wide, but patchy, range — throughout both the Atlantic and the Pacific Oceans. The species is generally found in relatively deep waters, but also seems to spend a fair amount of time in very deep waters — it’s been caught as deep as 5,150 feet.

The species grows to a length of roughly 6.6 feet, and possesses a dark (generally), eel-like body with most of the fins placed quite far back. The “frilled” part of its name comes from the “frilly or fringed appearance of its six pairs of gill slits”.

“Seldom observed, the frilled shark may capture prey by bending its body and lunging forward like a snake. The long, extremely flexible jaws enable it to swallow prey whole, while its many rows of small, needle-like teeth make it difficult for the prey to escape. It feeds mainly on cephalopods, leavened by bony fishes and other sharks.”

Hope you enjoyed our brief trip into the deep. 🙂 If you’re looking for something equally strange, but also quite a bit different, may I recommend a brief trip into the distant past?

Image Credits: E. Widder/Orca; MBARI; Screen Capture; University of Bremen; Screen Capture