Lighted Fish: Types, characteristics, habitat and more.

There are currently on planet Earth a lot of animals, some well-known and others not so much, with surprising characteristics. One of these characteristics, considered perhaps as the most curious, lies in those species that are able to produce light. We can mention from cockroaches to fireflies through some fish which are what you will know next. They are called lighted fish.

The main reason that makes them produce light is Bioluminescence, which can be caused by multiple factors such as chemical reactions or some particular organs.

Lighted fish:What is Bioluminescence?

It consists in producing and emitting light by living organisms, and is a sort of chemiluminescence. It occurs widely in marine vertebrates and invertebrates, as well as in some fungi and microorganisms including some bacteria. In some animals, light is produced by symbiotic organisms such as Vibrio bacteria.

A high percentage of the species that emit bioluminescence live in the sea, especially at depths with more than 200 meters, places where solar radiation doesn’t reach and total darkness reigns. Therefore, 75% of deep-sea animals depend on the ability to emit light.

Lighted fish: bioluminiscense

How is Bioluminescence Produced?

It’s  produced through a chemical reaction that produces light energy within an organism’s body. For a reaction to occur, the species must contain luciferin, a molecule that produces light when it reacts with oxygen. There are various types of luciferin, which vary depending on the animal that receives the reaction; many organisms also produce the luciferase catalyst, which helps accelerate the reaction. The light emitted by fireflies is an example of this reaction between luciferin and luciferase.

Another kind of chemical reaction that also allows some species to emit light is through ions, rather than enzymes. This allows the body to control the brightness of the light to release more or less protein, all this controlled by the nervous system of animals, in response to external factors.

Types of Bioluminescence

There are three main types of bioluminescence: intracellular, extracellular and that produced by the symbiotic relationship with bacteria. The first is that in which the chemical reaction is produced entirely inside the body of bioluminescent animals, through specialized cells. This type of bioluminescence is characteristic in several squids (firefly squids) and dinoflagellates.

Extracellular bioluminescence is when the reaction between luciferase and luciferin occurs outside the bioluminescent organism. Both components are stored in different glands inside or on the animal’s skin. When the light is needed, the substances are secreted to make the chemical reaction. This type of bioluminescence is common in some crustaceans and abyssal cephalopods.

The bioluminescence that occurs through symbiosis with bacteria is the most widespread in the animal kingdom, especially in marine animals such as mollusks, echinoderms, fish and worms. In several body parts of the bioluminescent animals there are small bladders, known as photophores, where they keep luminescent bacteria, which are activated or secreted when required.

What are the Functions of Bioluminescence?

Bioluminescence has a wide range of functions within the animal kingdom. All help bioluminescent species survive, whether to reproduce, feed or defend themselves.

As a defense system, bioluminescence is extremely effective: the light produced is used to scare or confuse predators. This is done by a set of flashes. Even some species shed bioluminescent limbs from their bodies as a distraction technique to prevent them from attacking vital organs, as do the Anomalopidae, the family of lantern fish.

Some species use the emission of lights to find a partner. Males use light signals to attract the interest of females, while females can respond to males with other light emissions. This technique is used by fireflies to reproduce. Another case may be that the brightness intensity of the emitted light demonstrates the male’s virility potential.

Bioluminescence is also used as an offensive technique. The clearest example is the species that use light as a bait, because some fish are attracted to the light and when they are close enough they are consumed. Also light can be used by predators to see better in the deep sea.

Let’s watch and learn

Lighted Fish and Human Beings

For lighted fish, bioluminescence is a matter of communicating and protecting themselves from being eaten or hurt, but for humans, the beautiful colors and light that are produced by these fish are commonly regarded as masterpieces.

A temporary exhibition at the National Museum of Natural History in 2012 explored these links between art and science. The artist Shih Chieh Huang created hanging installations in the dark space of the museum that lit up and seemed to float in the deep sea. Some artists use the same bacteria to create line drawings or entire exhibits with dishes full of bright single-celled organisms.

Bioluminescence can also be used as a tool by researchers to learn more about the ocean and its mysteries. Edie Widder, a bioluminescence scientist, was with a group trying to film the giant squid for the first time.

She suspected that the giant squid would be attracted to a bioluminescent light attached to a fake squid, not because she wanted to eat this little fake squid, but because her flashing light is a burglar alarm and this could mean that she had bigger prey nearby, her Theory proved correct.

Main Species of Lighted Fish

In this part of the post you will know about different species of lighted fish available in the ocean, let’s start.

Lighted Fish: Angler fish (Lophiiformes)

The Angler fish is known as one of the ugliest fish that exist given its weird appearance and characteristics. This fish has characteristics that make it very peculiar.

It belongs to the Lophiiformes order and flaunt a very unconventional appearance that make them characteristic. This order is divided into 5 suborders: Lophioidei, Antennarioidei, Chaunacoidei, Ogcocephaloidei and Ceratioidei.

Although they are known as the ugliest creatures in existence, their morphology has its explanation. Their body is adapted to survive in the inhospitable ocean depths where sunlight barely reaches and nutrients are scarcer. The fight for survival is much more complex since there are many predatory species.

As for its characteristic body, it has a very wide head and a flattened body that narrows towards the tail. One of the angler fish’ scariest aspects are their teeth, since their mouth is shaped like a crescent while their teeth are sharp and shaped inward. Lophiiformes usually have a brown or dark gray body color and a rough and flaky skin.

Due to the conditions in which they live, angler fish usually have thin and flexible bones that allow them to open their mouth enough to swallow their prey. To avoid being eaten or oppose some kind of resistance, they have long spines on the head. The dorsal and ventral fins are located on the back of the tail. Some species of angler fish have their fins modified to better adapt to the seabed and to be able to walk on it. Their size ranges between 20 centimeters and 1 meter in length while their weight is about 27-45 kilograms.

One of the anglerfish’s distinctive characteristics is the piece of spine that protrudes above their mouth similar to an antenna, which they use as bait to attract prey. This organ in some species of female has luminescence product of the symbiotic bacteria that inhabit it.

In some species, bacteria are unable to produce independent luminescence, suggesting that they have developed a symbiotic relationship and bacteria are unable to synthesize all the chemicals needed for luminescence by themselves, depending on the fish to make up the difference.

Here they are

Lighted Fish: Cookiecutter sharks, (Isistius brasiliensis)

This is a small and fierce shark that sticks teeth in prey much larger than it. Its name comes from its skill to rip perfectly circular pieces of its prey in the form of a cigarette burn.

Main Traits

The cigar shark (as it’s also known) can measure up to 50 cm (20 inches) in length and is one of the smallest sharks. Its rounded and brown body is much darker on the dorsal side and lighter towards the belly. It has a black collar or stripe on the neck; the fins are small and attached to the body.

The caudal fin or tail, drives this small shark from the sea depths. This species lives in the dark seabed and can be found at depths of up to 3,570 m (11,500 feet). At night, the cigar shark rises to the surface to feed, but spends the day in the depths. They can usually be found near Ecuador, where the waters are warm.

Its color is chocolate brown, with a dark neck that wraps around the gill region. The fins have translucent margins, (except the flow), which has a darker margin. Isistius brasiliensis has photospheres that densely cover the entire lower surface, except the collar.  Such structures produce a bright green glow and the maximum length recorded for this species is 42 cm.

The Cookiecutter sharks’ green luminescence can last up to three hours after it has been removed from the water. Ventrally positioned, photospheres serve to alter their silhouette from below by matching the descending light, a strategy known as counter-lighting, which is common among bioluminescent organisms in the mesopelagic area.

The individual photospheres are placed around the denticulate and are small enough so that they cannot be distinguished with the naked eye, suggesting that they have evolved to deceive animals with high visual acuity or that they are at close distances .

Let’s watch them

Lighted  Fish: Frog Fish, (Batrachoididae)

Batrachoididae are a family of marine fish, (the only one of the Batrachoidiformes order). We can find them in the Atlantic, Indian and Pacific oceans, with rare freshwater species.

The Frog fish’ Main Traits

These fish are in a wide range of sizes ranging from 5 to 57 cm in length and which have among their main characteristics a huge mimicry capacity spine elongation that simulating a worm or small fish , is used as a line as a fishing rod to capture its prey.

They are easily recognizable by their particular characteristics: large and crushed head, often with beards and other appendages.

Frog fish have a robust appearance very different from other fish. Their body, (which lack scales), is covered with spikes, irregularities and warts that allow them to be confused with sponges, corals and even rocks. They feed by hunting lurking on the bottom, from invertebrates and fish, preferably mollusks and crustaceans. To camouflage they present a brown body with some black spots, although some species that inhabits coral reef has striking colors.

Frog fish are regarded as the strangest creatures in the marine ecosystem, because its displacement is quite different than that of the other fish.

Frog fish owe their name to their long, thin tongue, which they use to hunt their prey, just as toads and frogs do. This is a creature that apparently moves very slowly, but when capturing its food it performs it so fast that it is very difficult to see it with the naked eye.

Frog fish have the ease of hiding and camouflaging, adapting their appearance to their surroundings and confusing with the landscape, what is known as mimics.  The more than 700 photospheres on their skin make of frog fish bioluminescent creatures which produce a fluorescent green glow.

Let’s meet them

Lighted Fish: Black Dragon Fish

The scientific name for this fish belonging to the Stomiidae family is Idiacanthus atlanticus.  It is found globally in the subtropical and temperate south oceans between the latitudes of 25º S and 60º E, at depths up to 2,000 meters.

 The species is sexually dimorphic, as the females are black with six stripes, and the males are brown and lack the females’ canine teeth. It is believed that females make a vertical migration of more than 500 meters per day, while the males do not migrate, remaining below 1,000 meters at all times.

Their length is up to 40 centimeters for females while males measures only 5 centimeters. Black dragonfish are bioluminescent, but unlike most of these predators, which use their light primarily to attract prey, Black dragonfish can see their own light using it to hunt. Their light is almost in the infrared and is barely visible for the human eye.

Japanese Pineapple-fish (Monocentris japonicus)

The maximum length of this species ranges between 22 and 25 centimeters. Its body is laterally compressed from the head to the tail and has yellow shades distributed like a network that resemble a pineapple, hence its common denomination.

Their striking body is covered with large and rigorous light and bright yellow scales, with dark edges.  The Japanese Pineapple-fish’s mouth is small and rounded crowned by small teeth and photopheres which have bioluminescent symbiotic bacteria.

It’s  thought that the photophores play the role of attracting the zooplankton on which they feed and for Intraspecific communication purposes.

Habitat and Customs

The pineapple fish lives between 6 and 200 meters deep. It is more common to see it swimming in shallow waters of  reefs,  and even at lower levels. They are very calm, since due  their morphology , swimming at high speeds is difficult for them. Thus, they  prefer to stay in unseen or hidden areas, usually in places with low light such as caves or among thick vegetation. In addition, it’s important to point out  their high-pitched sounds when they are stressed.

Let’s watch them


Believe it or not, up to 10% of sharks are considered bioluminescent, especially shark species that live in the deepest waters. Among them we have the previously mentioned cigar sharks.

An adult shark can have up to half a million of these photosphere organs. All these sharks produce luminescence, without the support of bacteria. Undoubtedly, these are impressive animals that demonstrate how wise nature is, and how each species develops special abilities and characteristics, usually with the aim of surviving in such a hard test that life is.

Abyssal Zone

The abyssal area is the part of the ocean that is located more than 2,000 meters deep in the sea. The area is mainly defined by its different environmental conditions which are very uniform, characteristic that is reflected in the different life forms that inhabit it. The abyssal kingdom is the largest environment for life on Earth, covering approximately 300,000,000 square kilometers, about 60 percent of the global surface and 83 percent of the ocean and seas area.

Abyssal waters originate from the air-sea interface in Polar Regions, mainly in Antarctica. In these waters you can find very uniform concentrations of salts and nutrients such as nitrogen, phosphorus and silica, even much higher than in the above-lying waters.

This is because abyssal waters are the reservoir of salts of decomposed biological materials that settle down from the upper areas, and the lack of sunlight prevents their absorption through photosynthesis.

Characteristics Of The Abyssal Area

  • The oxygen content in abyssal water depends entirely on the amounts found at its polar site of origin and the absence of the photosynthesis process, which prevents the introduction of new oxygen into the depth.
  • Abyssal waters retain several cubic centimeters of dissolved oxygen per liter, because dispersed animal populations don’t consume oxygen faster than enters the abyssal zone.
  • Abyssal life is concentrated on the seabed; however, the water closest to the floor may be essentially depleted in oxygen. The abyssal area is a very quiet place, and stays away from the storms that affect the oceans.
  • It is usually far enough away from the earth that the sediment is predominantly composed of microscopic traces of plankton produced in the food chain in the above-lying waters, where they sit.
  • Abyssal sediment in waters below 4,000 m in equatorial regions consists mainly of the calcareous shells of zooplankton and phytoplankton, known as cocolithophores.
  • Below 4,000 m, calcium carbonate tends to dissolve, and the main constituents of the sediment are the brown clays and silicium remains of the radiolary zooplankton and phytoplankton as diatoms.
  • The abyssal zone is located between 3,000 and 6,000 meters deep, below the area known as the batiphagic and hadopelagic zone.
  • The temperature of the abyssal area is very cold and has a fairly high hydrostatic pressure. It has a large shortage of nutrients and has no natural light.
  • Underwater accidents such as mountains, mountain ranges, plateaus and islands of volcanic origin may occur.

The Abyssal Area Fauna

The fish that inhabit the abyssal zone are known as abyssal fish. These creatures tend to be gray or black, they aren’t  very structured and without lines. Mobile shapes have long legs; and the animals tied to the bottom have stems, allowing them to rise above the nearest layer of water to the bottom, where oxygen is scarce.

Crustaceans and abyssal fish can be blind. With increasing depth, carnivores and scavengers become less abundant than animals that feed on mud and suspended matter. Abyssal animals are thought to breed very slowly. Certainly the animals that inhabit this area are very strange and have a monstrous appearance.

Most are also bioluminescent, which helps them attract prey and avoid some dangers. Abyssal gigantism can also be found, which includes animals as large as sea chandeliers measuring more than 1.50 meters. Among the species that we can find are: the giant squid that manages to measure between 17 and 19 meters long, the dragonfish, ballfish, crystal squid, dumb octopus, yeti crabs  and axefish.

Abyssal Area Flora

The flora that inhabits the abyssal zone feeds mainly on debris that fall to the bottom of the sea from the surface. Because sunlight cannot reach, plants aren’t able to perform the photosynthesis process, so there are no green algae. In some of the places where hydrothermal sources are present, which depend on the energy of the volcanoes is chemo synthesis, which develops some bacterial species.

let’s learn more about this interesting area.


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