Deep-sea fish are the strangest creatures that exist on Earth. Their appearance is awe-inspiring

Sea monsters appear in many myths and legends. However, you don’t necessarily have to look for them on the pages of books. Deep below the surface of the water live deep-sea fish. They are creatures that are directly difficult to imagine.

Deep-sea fish inhabit the darkest regions of the seas. They are found in parts of the oceans where sunlight no longer reaches. The zones where they are primarily found are called batial and abysal. The first of these, the batial or batial zone, covers waters from 1,000 to 4,000 meters below the surface. The abysal (or abyssal zone) is the depths from four to six kilometers below the water table.

At such great depths, conditions for life are very difficult. In addition to the lack of light, all marine animals must also cope with low temperatures, small amounts of oxygen and very high pressure. Pressure increases with depth — by one atmosphere for every 10 meters. This means that five kilometers below the surface of the ocean, the organisms living there must withstand pressures 500 times greater than at the surface.

How have deep-sea fish adapted to living where the pressure is so high? One adaptation is the absence of a swim bladder — that is, a chamber (sometimes consisting of several parts) filled with gases. The swim bladder makes it easier for fish to submerge and surface, but it has secondarily disappeared in deep-sea fish.

Many changes have also occurred in their bodies at the molecular level. For example, they have chemical compounds in their cells that protect them from deformation under high pressure.

What do fish from the ocean floor feed on?

Kilometers below the surface of the water there is not only light, but also no plants. The fish living there have two choices when it comes to getting food. The first is to catch the remains of plants and animals, falling from higher layers of water. The second is predation.

Both ways require good orientation in the area. Therefore, many deep-sea fish have developed various types of light organs (or photophores). These help attract and then capture prey. For example, matron fish, which live at a depth of four kilometers, have a luminous antenna (illicium) on their head that looks like a fishing rod. In fact, these are specially transformed dorsal fins. At depth, they act as a decoy.

Many organisms living in the deep have the ability to bioluminescence — that is, to glow. Catching even the faintest source of light can be crucial for a fish. That’s why some species of deep-sea fish often have huge eyes. They allow them to perceive even the faintest light stimuli.

Some of the largest eyes are those of Xiphias gladius, which lives at the edge of deep water, that is, 900–1000 m below the surface. The diameter of the eyes of this fish is 9 cm, which is about 3 percent of the body length (3 m). Interestingly, swordfish have special organs for raising the temperature of the eyeballs, which significantly improves the ability to see, and thus the effectiveness of hunting.

Other species of deep-sea fish

Many deep-sea fish have an uncanny appearance. Some can directly resemble monsters. For example, fish from the family Eurypharynx pelecanoides are quite impressive. These fish have huge jaws and a huge throat that looks like a skin sack in pelicans. The rest of their body is reduced, making swallows look like floating heads propelled by a thin tail.

The fish of the Melanocetus johnsonii species also have a huge sack under their throat. They live at a depth of one and a half to two kilometers, where sunlight no longer reaches. So these fish attract prey using bioluminescence. They have such an extensible stomach that they are able to swallow prey weighing more than themselves.

Chauliodus sloani can also be frightened. It has a very long body ending in a large head with huge teeth. Thanks to a light organ, this fish lures prey into its wide-open mouth, which it then closes like a trap.

The strangest fish of the deep

One of the most famous deep-sea fish is Psychrolutes marcidus. This name is unlikely to tell anyone anything, but already the English blobfish — perhaps so. The blob fish lives at a depth of about one kilometer. However, when it is brought to the surface, its gelatinous body swells and spills, giving it a strange appearance. To people who easily succumb to pareidolia — that is, seeing familiar things in different shapes — the blob fish begins to resemble a swollen, sagging face.

On the other hand, Albatrossia pectoralis, one of the most common deep-sea fish, consists of an ominous-looking head with a large snout and a long fleshy tail. It is found at depths ranging from several hundred to 3.5 kilometers. It can be up to two meters in length. It is estimated that these fish make up as much as 15 percent of the entire population of deep-sea fish.

Iconic deep-sea fish are also representatives of the genus Anoplogaster. We know of two species of these undersized fish that have been found as far as five kilometers below the surface. They have disproportionately large teeth and twisted mouths, which gives them an unpleasant, off-putting appearance. However, they are completely harmless to humans.

The same can be said of the extremely rare shark Mitsukurina owstoni. This shark, although it looks ominous, feeds on cephalopods, crustaceans and fish. It has protruding jaws (so this shark may have inspired the authors of “Alien”) and a distinctive long beak. The fish feeds at several hundred meters — the deepest place from which it was fished was 1,300 meters below the surface.

What lives at the bottom of the ocean?

What fish live at the greatest depth? Just last month, scientists picked out a new record holder. This was achieved by a Japanese-Australian scientific expedition studying the Izu-Ogasawara Trench, which is up to 10 km deep.

At a depth of 8336 m below the surface, a fish belonging to Pseudoliparis, a genus of demersal fish living in the greatest depths of the Pacific Ocean, was recorded.

According to the researchers, “there is a certain limit below which no fish could live anymore. It amounts to about 8400 meters. Below it, cellular biochemical processes that protect deep-sea fish cells from high pressure cease to function”.

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