Deep-Sea Fish

About the Deep Sea Fish

The aquatic bodies of the planet earth are home to so many fishes among them the deep sea fish or the deep ocean fish which are of the class Osteichthyes and they are the most intriguing and researched aquatic creatures. They survive in deep waters and dark surroundings under all the pressure from the water above. The deep sea fish thrive in areas under the ocean where even sunlight fails to reach due to its depth, which is bound to make marine biologists curious about this species. The depth when 200 metres and below the pressure increases and the fishes surviving in such depths of darkness are called deep sea fish. They even live up to under 8370 metres. The fishes that live under the deep ends have special features for different conditions than the sea level. 


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Lifecycle of the Deep Sea Fish

  • The eggs or larvae of the fish have oil in the plasma as they stay in a buoyancy environment in the pelagic zone at this stage. 

  • Many of them are born in the shallow waters and as they mature they sink into the depths of the sea. 

  • Upon maturation, they no longer float in the buoyancy state and the weight increase makes it denser than the seawater and helps them develop hydrofoils in order to provide hydrodynamic lift, unlike other fishes which at this stage develop swimmer’s bladders.

  • The fish also tends to develop spines as a defence mechanism except for the mesopelagic fish that usually lack defensive spines. The mesopelagic fish and use colour to camouflage themselves from other fish.


Features of the Deep Sea Fish 

There are many deep sea fish representative species that lie like the deep saltwater fish under the vastness of the sea level and each has some special features depending on their class or family.

  • More than a dozen families of marine fishes are mid-water species and they are distinguishable due to their enlarged eyes, enormous mouths, and the presence of luminous organs.

  • The luminous organs can be present on several parts of the body of the deep ocean fish and they are often used to prey, communicate or be safe from predators and even for mating.

  • The deep sea fish have the most specialized features of any species in the world that has evolved for them to adapt to extreme conditions like high pressure, the darkness of the environment and cold.

  • The deep sea fish do not have any air sacs in their body so that they do not compress under the extreme pressure of the sea as they lay deep.

  • Their luminescence organ is a unique feature that can be present anywhere in their body.

  • Some deep sea fish use their needle tooth and even their sharp fins to prey.

  • Their bodies are expandable for them to be able to consume prey that is bigger than them.

  • They have hinged jaws wherein the teeth extend to the front beyond their mouth due to their large size.

  • A component called rhodopsin present in the eyes helps them to see even in the dim light.


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Different Deep Sea Fish Representative Species

The deep sea fish can be located in various zones of the sea and for each zone, the pressure keeps rising and the oxygen levels along with the temperatures keep on declining and they adapt their bodies to such environments.

  1. Benthic organisms are the ones that live on the surface sea level the ones below its pelagic and epipelagic zone and of them, the marine species that inhabit the pelagic zone are only 2 per cent.

  2. Even the organisms that inhabit the 200-1000 metres deep mesopelagic zone start to exhibit luminescence producing ability that is a characteristic feature of the deep ocean fish. In this zone, light is still measurable and below this in the depths are darker. 

  3. The bathypelagic zone that is 1000 to 4000 metres deep is the first zone inhabited by deep-sea organisms. 

  4. The abyssopelagic zone of 4000 to 6000 metres deep is the home of the deep sea fishes. 

  5. The zones where there is not a single trace of penetrated light called the aphotic zone are the bathypelagic and abyssopelagic zones where 75 percent of the ocean life inhabit.

Let us look at some of the deep sea fish at different depths of the ocean and their special characteristics:


Characteristics of Deep Sea Fish at Different Depths 

Deep Sea Fish Names 

Species of the Deep Water Fish 

Depth of the Deep Ocean Fish

Characteristics

Lantern Sea Fish

Myctophidae family 

Live in the depths to 300 metres at daytime and come to the surface level at night time.

They account for much of the biomass about 65 percent of them and are responsible for the deep scattering layer of the world's ocean.

  • elongated fish

  • largemouths and eyes

  • numerous light organs on their head, underside, and on the tail base.

Viperfish Sea Fish

Chauliodus species

400m to 1km in the deep waters 

  • A fierce predator.

  • The big fangs slide in front of its mouth, not allowing it to close.

  • Preys on fish, crustaceans and squids.  

Stoplight loosejaw Sea Fish 

Malacosteus niger

500m to 1km into the deep waters one can find them.

  • Emits red light making it the only fish with this ability. The light produced serves as a torch and is invisible to both the predator and the prey.

  • Red light is also used as a mode of communicating and finding others of its species.

  • Has needle-sharp teeth with hinged jaws and neck.

  • Preys on shrimps and other small fishes. 

Footballfish 

Himantolophus groenlandicus

Found in the deep waters ranging from 200m to over 1km

  • Also known as the man-gobbler.

  • This deep sea fish is known to be found in extreme depths.

  • The footballfish is covered in spines and as the name suggests is the size of a football.

  • Possesses branches with glowing lights at the end that starts from the head.

  • The lights are mainly for attracting the prey.

Black seadevil Sea Fish 

Melanocetus johnsonii

At depths ranging from 250m to 2km 

  • Can swallow prey larger than themselves due to their stomach.

  • Males are relatively much smaller than females and possess enormous nostrils for mating purposes in the dark.

  • Female black devil sea fish has a light organ on a stalk between their eyes and have bigger teeth. 

Rattail Sea Fish 

They are also called grenadiers belonging to this species from the Macrouridae family.

Ranges from 22 m to 2.2km and can sometimes reach more than a metre in length.

  • Lives in shallow waters near the coast close to the seabed.

  • Preys on shrimps, fishes and squids and is extremely sensitive to the vibrations made by its prey.

Coelacanth Sea Fish

Latimeria chalumnae

Found in depths of 150m to 400m in the deep sea. 

  • It has leg-like lobed fins due to which it was considered to be a missing link between fishes and amphibians.

  • They have an unpleasant taste so fishermen consider it worthless.

  • Its existence in science is known only since 1938.

  • It is considered to be the most famous living fossil as it was considered dead 85 million years ago but again found in 1938. 

Mariana snailfish

Pseudoliparis swirei

It thrives at the depths of 8,000 meters.

  • It is a top predator along the Mariana trenches where it is found.

  • It is a recently discovered deep sea fish and as of writing holds the crown for the deepest living sea fish.

  • They prey on tiny crustaceans.   

Deep sea Anglerfish

Melanocetus johnsonii



Lives in the aphotic zone at about 2000metres depths. 

  • Also known as humpback anglerfish, it is about 18 centimetres in length and is medium-sized.

  • Numerous small skin spines are found under the dorsal fin that they use to attack their prey for food. 

  • They have long pointed teeth and short, globular bodies, large heads with a widened mouth that is nearly vertical. 


Deep Sea Fish Facts

  • They have a very unique appearing transparent skin.

  • The deep sea fish have black bodies and even silvery bodies.

  • They have uniquely large eyes that they have adapted through an evolutionary process from ages to be able to work through in the dim deep sea. 

  • Some of the deep sea fish that consumes prey larger than their size consumes by grasping with the help of their tentacles that have suction cups attached to them.

  • Many deep sea fish are monstrous-looking creatures and ironically very small in size to which the giant squid is an exception. 

  • Atlantic wolffish, a type of deep ocean fish produces its antifreeze in the cold temperatures to keep the blood flowing. 

  • The viperfish can stretch its stomach to double the size of its own body and this expandable nature is also an adapted mechanism to feed and survive. 

  • The “vampire squid”, a type of cephalopod when under attack can turn itself inside out as a defence response.

  • The blobfish can decompress itself when taken out of the depths.

  • The male flabby whalefish when it reaches adulthood loses its oesophagus and stomach by fusing its mouth and stopping to feed itself. With this mechanism, it grows a massive liver with whose support it lasts a lifetime. 

  • The slender snipe eels are very thin and long and have their anus located in their throat region.

  • The deep sea fish eat the scraps that reach the bottoms or feed themselves by eating each other to survive as there are no phytoplanktons due to the absence of sunlight beyond the mesopelagic zone. 

FAQs (Frequently Asked Questions)

1. Can We Find Deep Sea Fish in Shallow Waters?

Ans. The deep sea fish have evolved to adapt to the conditions of the deep waters and have developed a different kind of cell membrane to thrive under such conditions of high pressure. In the case of some fishes who live in shallow waters where there is low pressure the deep ocean fish will fail to adapt to such changed conditions and will not survive. An exception to this is the lanternfish that often resurfaces to the sea level at night and sinks to its original depths in the daytime. 

2. Do Deep Ocean Fish Get Crushed Under Water Pressure?

Ans. The water pressure is very high in the deepest part of the oceans. Like in the Atlantic ocean 840 bars of pressure are 840 times higher than the pressure experienced by the aquatic animals on the sea level. When you dive deep into the pool you might experience an unpleasant sensation sometimes painful in your ears and that is because your body under such pool water pressure in deep areas crushes the air sacs of the body. And the deep ocean fish thrives without getting crushed because of the absence of such air sacs in their bodies which is very much present in other fishes that live in the shallow water region that help them sink or float up.

3. Are Deep Sea Fishes and Deep Saltwater Fish Edible?

Ans. It is a known fact that fish rearing and harvesting has been an ancient practice for its source as a portion of food for the source of protein and omega fats and good oils to many people. Deep sea fish is also a popularly consumed food among many. The most common of all the deep saltwater fish are the anchovies, the other deep sea fish include Bass, Black cod which is also called Sablefish, Bream, Catfish, Dogfish, Eel, and Flounder.

4. What Kinds of Fishes One Must Avoid Eating?

Ans. There are many compositions of fish like mercury and PCBs or polychlorinated biphenyl that are industrial compounds when often drained in water bodies consumed by the fish. The EDF (Environment Defend Fund) recommends avoiding such fish with high PCBs and mercury that can be toxic and cause high damage to the liver and even lead to infertility and cancer. The kind of fish one must avoid are Bluefin Tuna, Chilean Sea Bass which is also called Patagonian Toothfish, Monkfish, Grouper, Orange Roughy, and the farmed salmon that is commonly labelled as ‘Atlantic Salmon.’