The strange fish that inhabit the deep oceans are some of the most fascinating creatures found anywhere on our planet.
They’re also capable of rivaling the ugliest and most scary-looking.
So, why are deep sea fish so ugly?
It’s because they’ve adapted to survive in the incredibly harsh environment that is entirely different from shallower waters, where you’ll find the “prettier” fish.
Deep sea fish have evolved for practical purposes rather than to win a beauty contest.
Whether related to the low temperature, the complete lack of light, the incredible water pressure, catching the available food to eat, or hiding from predators, the properties that make deep sea fish “ugly” to humans exist for a very good reason.
Why Are Deep Sea Fish So Ugly and Scary?
The ocean depths are a very different world compared to the relatively shallow waters where the fish we are most familiar with are found.
Deep sea fish have to survive in some of the harshest conditions on earth. They live without light, under extreme pressure, at low water temperatures and oxygen levels, and have scarce food supplies.
Why do deep sea creatures look weird? It’s because they’ve evolved the characteristics needed to survive in these extreme conditions, and these can make them look weird or ugly by human standards.
The requirements to successfully live, search for food and reproduce in the deep ocean are not the same as those needed closer to the surface.
As we answer “why are deep sea fish so ugly?”, it’s worth remembering that what we see as ugly or scary is a vital characteristic that allows the fish to stay alive.
What Is the Deep Sea?
To understand deep sea fish, it’s worth considering what the deep sea is.
The deep ocean begins below 1,000 m (3,280 ft) by most standards.
The surface waters that receive sunlight are called the epipelagic zone and extend down to 200 m (656 ft). The second layer is the mesopelagic zone between 200 m and 1,000 m (3,280 ft) deep.
This minimal light layer isn’t considered the deep sea proper, although some fish living here display “deep sea” characteristics, such as bioluminescence.
The deep ocean begins in the bathypelagic zone (1,000–4,000 m / 3,280-13,123 ft deep) and extends down into the abyssopelagic (4,000–6,000 m / 13,123-19,685 ft deep) zone and beyond.
These layers are in complete darkness, and because of the extreme depth, anything living there exists under incredibly high pressure.
Dissolved oxygen levels are also low, and the water temperature can range between a very cold -1.8 and 3 °C (28.76-37.4 °F).
These conditions result in a very different living environment than, for example, a sun-drenched, tropical coral reef.
Surviving in these extreme conditions requires evolutionary adaptations that make deep-sea fish look very different. Huge mouths with long sharp teeth, massive eyes, glowing bioluminescence, and odd-shaped bodies are very common.
Let’s consider the different conditions separately to try and work out how they make the scariest and ugliest fish
The lack of light removes any need for bright colors or patterns on deep sea fish. Instead, more sinister dark colors like black or red (which appears black) are required.
Many deep-sea critters use bioluminescence to produce light patterns across their bodies. These fantastic displays of light, where there is none naturally, are used for camouflage, attracting prey, to communicate to a mate, or even as a dazzling defense mechanism.
Some deep sea fish have giant, scary-looking eyes, and they’re typically tuned to detect movement or differences in tone in the dark rather than colors or light. Other fish may have only tiny eyes or none at all.
Fish with tubular eyes with large lenses have evolved to only look upwards and detect predators or prey silhouetted above.
There’s very little food in the expanse of the deep marine waters, so fish need to be equipped with weird-looking adaptations that let them grab whatever they come across.
Ambush predators that sit and wait for their food have mouths filled with long, fang-like teeth ready to capture anything edible.
These mouths are often oversized with hinged jaws that, together with giant stomachs in expandable bodies, allow the fish to take advantage of any meal, even if it’s bigger than they are.
Other deep sea fish, like the deep-sea anglerfish, have a frightening-looking bioluminescent “fishing rod” to lure prey to their mouths.
The extreme ocean pressures mean deep sea fish have cellular and physiological adaptations that make them look very different from more familiar shallow-water species.
Successful deep water fish have evolved to use as little energy as possible, so they often lack the muscular, streamlined forms needed to swim long distances and instead have weirdly elongated or compressed body shapes.
Many species don’t even have a swim bladder. Some don’t have scales and will instead have slimy skin.
Deep Sea Fish May Look Even Weirder if Brought to the Surface
It’s worth being aware that while deep water fish can look scary, some photos you see might make them look stranger than they naturally are.
If a fish is brought up to the surface, highly pressurized gasses inside their bodies can expand, causing them to deform dramatically.
So, if you see any really odd photos of deep-sea fish, be aware that they may not naturally show how the animal looks.
7 Ugly Sea Creatures From the Deep Sea
The ocean’s ugliest animals are also some of the least well-known. Scientists are continually making discoveries about these ugly sea creatures that make deep-sea animals as fascinating as they are peculiar looking.
The Blobfish (Psychrolutes microporos)
The blobfish is a creature with the dubious title of being the mascot of the Ugly Animal Preservation Society.
This deepwater fathead lives in the abyssal zone around New Zealand and Australia, and specimens, including one known as “Mr. Blobby” displayed in the Australian Museum, have been found in waters over 1,000 m (3,280 ft) deep.
The world’s ugliest fish has a flabby, off-white colored body with a slimy gelatinous surface.
The ambush predator uses its wide mouth to grab whatever is available as this ugly fish drifts with the currents over the seabed.
Deep-Sea Anglerfish (Lophiiformes)
Anglerfish are probably one of the best-known deep water fish species thanks to the bioluminescent lure the female of the species uses to attract their prey.
The deep-ocean species covers both the ugly and scary categories with their unusually shaped bodies, giant heads, and large mouths filled with translucent fang-like teeth that are curved inwards to ensure that any prey cannot escape.
Barreleye Fish (Opisthoproctidae)
The barreleye, also known as the spook fish, is an impressive creature that’s strange looking and perhaps a little ugly. It also has a fascinating way of seeing.
Within the transparent head of the ugly fish, there are green semi-spherical eyes that look upwards and scan for the faintest shadow of food drifting down from shallower water.
Monkfish are ugly bottom-dwelling monsters that have wide mouths filled with rows of frightening wide teeth.
The various species of monkfish have mottled skin on their flattened bodies and only small eyes on their broad heads.
To take advantage of almost any food they come across in the dark depths, monkfish have distensible stomachs that allow them to eat a meal nearly as big as the ugly fish itself.
Goblin Shark (Mitsukurina owstoni)
The rare goblin shark makes the world’s ugliest fish list thanks to its flabby body covered in pink skin and the bizarre-looking long snout that sticks out of its head above some nasty-looking protruding jaws.
This ugly fish is often called the “living fossil” thanks to its prehistoric appearance.
Luckily, it isn’t a shark that you’re likely to meet, as although they occasionally reach waters as shallow as 100m (328 ft), they’re typically found much deeper like at the Mariana Trench.
Illuminated Netdevil (Linophryne arborifera)
We’ve already mentioned anglerfish in general, but this particularly ugly fish species is worth a special look.
The female netdevil doesn’t just have a bioluminescent lure sticking out of the top of her head. She also has a weird branched barbel “beard” hanging from her lower jaw that also glows.
If the ugly apearance isn’t enough, the tiny male of this ugliest fish species acts as a parasite and bites into the female to permanently attach and obtain its nutrition.
Pointy-Nosed Blue Chimaera (Hydrolagus trolli)
Also known as the ratfish, this is undoubtedly one of the ugliest fish.
The chimaera’s skin is blue-gray and appears almost smooth, like leather.
Although fascinating, the chimaera has a face you can only describe as ugly. The short-pointed snout and deep-set eyes give the fish a mischievous, perhaps evil appearance.
To finish off, the dorsal fin is topped with a sharp venomous spine, so it’s deadly as well as ugly.
7 Scary Deep Sea Creatures
Scary deep sea creatures could easily be the cause of nightmares.
You can sleep safe knowing that all these beasts are only found in their natural habitat, under thousands of meters of water, far away from where you may swim.
Sloane’s Viperfish (Chauliodus sloani)
What is the creepiest deep sea fish? For us, it has to be the viperfish.
Imagine coming face to face with its wide jaws filled with needle-sharp teeth. This would be the definition of scary!
Sloane’s viperfish even holds the Guinness Record for the largest teeth relative to head size, so you can tell nature has designed it as a hunter.
The jaws can open up to 90° to catch prey, like the viperfish’s favorite meal of Lanternfish, which can be up to two-thirds the size of the viper itself.
Deep-Ocean Hatchetfishes (Sternoptychinae)
These odd-looking guys are amazing and scary in equal doses!
The hatchetfish get their name from their odd bodies that have a thin rear section that makes them resemble a hatchet ax to some people.
Their heads have large eyes that bulge as if the fish has just witnessed something frightening. In reality, they’re designed to spot any food hiding above them.
Frilled Shark (Chlamydoselachus anguineus)
If you were unlucky enough to meet a frilled shark underwater, its eel-like appearance that twists and bends as it hunts would be enough to be frightening.
However, things would get really scary after one look in the shark’s mouth that’s filled with at least 300 curved needle-sharp teeth.
These teeth grip the shark’s prey and leave no possibility of escape.
Once the unlucky meal is held tight, the frilled shark will swallow it whole to be digested at its leisure.
The hagfish simply must be on any list of scary fish.
This frightening-looking, slime-covered beast hasn’t changed much in 300 million years and looks like something from horror fiction.
The feeding habits of the hagfish match its nasty appearance. The fish burrows into the carcass of whatever large fish it comes across and then slowly eats it from the inside using rasping cartilage teeth.
Gulper Eel (Saccopharyngiformes)
The gulper eel is another animal from the deep ocean that specializes in swallowing food much larger than itself.
Just imagine coming across a relatively thin eel only for its mouth to open up to the equivalent of nearly a quarter of its total body length. Quite scary!
Ghost Sharks (Chimaeriformes)
The last scary fish looks like something that could haunt your dreams.
The ghost-like form of the shark drifts along their natural habitats above the ocean floor, looking for food.
A venomous spine warns off potential attackers in the ghost shark’s dorsal fin that can deliver a potent sting.
As we’ve answered, “why are deep sea fish so ugly?” we’ve seen that the extraordinary and sometimes frightening-looking appearances they have are due to the incredibly harsh environment that they live in.
The combination of a world of complete darkness, colossal pressure, extreme cold, and scarce food mean that these fish have developed to look completely different from their shallow water cousins.
As they battle to survive in some of the harshest conditions on earth, we should consider that what can be called strange, ugly or scary is a vital evolved property that allows these incredible fish to survive.
British-born Dan has been a scuba instructor and guide in Egypt's Red Sea since 2010.
Dan loves inspiring safe, fun, and environmentally responsible diving and particularly enjoys the opportunity to dive with sharks or investigate local shipwrecks.
When not spending time underwater, Dan can usually be found biking and hiking in Sharm's desert surroundings.