In the depths of that dark ocean, there are often some swimming dots of "lights", which are all kinds of strange luminous creatures. They come and go from south to north, suddenly fading, emitting cold light, orange, red, yellow, green, blue, purple and other colors, as if they are shooting stars and fireworks, and like a colorful "lantern party" held in the "Underwater Dragon Palace", bringing light and life to this wonderful underwater world.
This phenomenon of bioluminescence has long been known, the most famous of which is the fireflies on land. In fact, there are many creatures that can emit light, protozoa, coelenterates, worms, link animals, crustaceans, insects, mollusks, echinoderms, fish, and even birds, all of which can radiate beautiful light in various forms.
Bioluminescence, also known as bioluminescence, is a luminous phenomenon caused by the chemical reaction of some substances in the organism, that is, the conversion of chemical energy into light energy. Therefore, bioluminescence is a kind of "chemiluminescence". The luminescence process of bioluminescence and artificial light sources is not the same. Artificial light sources (such as electric lights, etc.) emit a lot of heat while emitting light, but when you hold the firefly in your hand, you will only see it flash and shine, but you will not feel the heat, which is the essential difference between the above two light sources.
Different kinds of organisms, the way of light is not the same, generally speaking, can be divided into the following three types:
One is "intracellular luminescence". The luminescence of this method, the whole process is carried out in the luminous cells in the organism, which is the luminescent system of luminescent proteins that do not need oxygen under the action of calcium ions. Such creatures have specialized luminous organs. The glow of fireflies belongs to this kind.
One is "extracellular luminescence". Organisms that emit light in this way, in the process of luminescence, the luciferin and luciferase that cause luminescence are discharged from the luminous cells, met in vitro, and emitted light after oxidation due to the release of light quanta, such as sea fireflies, stigma worms, phosphorus worms and other luminous animals in the ocean.
There is also a "symbiotic bacterial luminescence", such as some luminous fish. Due to the cohibian luminescent bacteria attached to the fish's body, these luminous bacteria emit a bright light during metabolism.
In the ocean, with the exception of reptiles and mammals that return to the ocean twice, there are luminous species in almost all fauna. The luminous species identified include about 50 species of protozoa, more than 100 species of coelenterates, more than 50 species of worms, more than 200 species of molluscs, more than 150 species of crustaceans and about 300 species of fish.
Although some offshore fish can also shine, such as European cod, American toad fish, China's coastal seven-star fish and so on. But most of the glowing fish in the ocean inhabit the deep sea. According to ichthyologists, fish living at a depth of 3,000 meters have about 45% of the species with luminous organs, such as horned sharks, horned catfish, goldeye seabream, long-tailed cod and lanternfish and other wide-mouthed fish, are luminous fish.
The depths of the ocean are far less well-lit and nutrient-dense than in shallow water, the flow of water is strong and powerful, and the changes in temperature and salt are obvious. In the deep sea, the sun's rays do not penetrate, there are no plants or few plants; there are no waves, and the water flows rather slowly; the seabed is composed of soft, even semi-fluid silt and clay; the temperature is low, always maintained at 0 ° C to 2 ° C; and the salt content of the sea water is also very fixed. In addition, in the deep-sea region, carbon dioxide approaches a liquid state and leads to a continuous dissolution of calcareous matter.
Therefore, the scientific community once believed that there could be no life in such a dark, low temperature, and strong pressure deep seabed. Because in 11,000 meters of deep water, the pressure per square centimeter is greater than 1,000 kilograms! Until the 1930s, Scientists in the United States caught animals at a depth of 923 meters underwater. In 1949, Soviet biologists obtained specimens from a depth of 8,000 meters in the Pacific Ocean. Later studies further showed that although due to unfavorable living conditions, deep-water animals are not as developed as animals with high water levels in terms of quantity or quality, but in the depths of the ocean, life is still diverse, and the harsh living environment of the deep sea has also created deep-sea animals with special adaptability, and has many of the same characteristics in body structure, and many deep-sea animals have their own luminous organs as one of them.
The luminous organs of fish generally evolve from the epidermis and dermis, the structure is more complex, and the luminescence is often controlled by its nervous system. The structure of these light-emitting organs is very clever, usually located in a transparent light-emitting shell, with multiple layers of film on it; the bottom layer is smooth and transparent, which is a reflective film; the second layer is a light-emitting film composed of light-emitting cells and nerve cells, which is the main part of the light-emitting device; the third layer is a transparent delivery film, which specifically supplies the oxygen and moisture required by the light-emitting device; the outermost layer is a transparent light-emitting shell film, whichse main role is to protect the light-emitter.
The size, number, shape and location of the light-emitting organs on the fish body also vary according to the type of fish. Most fish's luminous organs are distributed on both sides of the abdomen, but some grow under the eye margin, on the dorsal side, on the tail, or at the end of the tentacles. For example, the long-tailed cod, a deep-sea fish that inhabits the bottom of the ocean, is named after the long tip of the tail. Its light emitters are mostly located under the skin near the abdomen or anus, and there are also luminous bacteria inside.
The long-tailed cod relies on contracting muscles to expel the light-emitting bacteria from the opening of the light-emitting apparatus and emit light. The golden-eyed seabream, which lives in a rocky area of 200 to 600 meters deep sea, has a luminous device located below the eye and looks like a tourist with a lantern. It was a fish that existed about 100 million years ago at the end of the Mesozoic Era and is presumed to be the ancestor of the most prosperous perch today. They have primitive features such as soft tendons of the ventral fin and caudal fin, as well as evolutionary features such as the dorsal fin and spines in the dorsal bone. The light emitters of the horned shark living in the deep sea are small, scattered in the skin, simple in structure, numerous, and can emit a strong and brilliant light green light. Even after 3 hours of death, it glows. The horned shark is very recognizable in appearance, and its two dorsal fins have a very hard spine (called spines) in front of them, commonly known as "horns", so the name horned shark.
The most interesting of the glowing fish is the species of lantern fish. Lantern fish are small deep-sea luminous fish, a total of about 376 species, China has 48 species, including feng lantern fish, pointed lamp fish, brocade lamp fish, star lamp fish, amber light fish, bright light fish, bottom light fish, strong light fish, standard light fish, cteno lamp fish, rainbow light fish, rare lamp fish and so on. Lanternfish have many luminous organs on both sides of the head and the ventral surface of the body, with more than 20 locations, and the light emitters in each part have special names, such as preorbital light emitters, nose dorsal light emitters, gill lid light emitters, gluteal light emitters, etc., which has become one of the important bases for classifying them.
Scientists believe that the benefits of the glow of deep-sea fish are manifold. For example, the connection between most of the luminous fish races is carried out by luminescence. Because various luminous fish have different numbers of luminous organs, their position and the intensity of luminescence are different, so it becomes a sign of identification between species and thus interconnection. In particular, these fish emit bright lights as a courtship signal every reproductive season, inviting the opposite sex to come to mate and achieve the purpose of reproduction. Glowing also makes them effective against predators. For example, the tail chaser of some lanternfish can suddenly emit a light, borrowing a sudden light curtain to surprise the enemy, but he himself takes the opportunity to slip away.
Some luminous fish also make full use of the favorable conditions of luminescence, setting traps to lure phototropic organisms as bait. The deep-sea fish Horned Trout is a famous example.
The horned trout was first known for the peculiar parasitic life of males. Its adult male is small and parasitizes females several times or even ten times larger than it. The male's lips and tongue are so tightly connected to the female's skin that they cannot be separated at all. Moreover, the organs of the male fish, except those related to reproduction, are almost completely degraded, and it is no longer possible to find the obvious features of the organs such as the mouth, jaw, teeth, fins and gills in them, so they can only survive by sucking the blood flowing from the female fish.
The female has a rounded body, a large mouth, a long, soft, and movable dorsal fin bone line on the head, and a large spike like a small lantern at the tip, like a fishing rod. The luminous bait on its "fishing tackle" is the illuminator transformed by the extension of the dorsal fin. They often hide their bodies in the mud and sand, sticking out the line, and really look like an "old fisherman" carrying a fishing rod. Those light-seeking fish who see the light and run over will often mistake the small lantern swinging in the water for delicious food, go up to a bite, and try to swallow it, and the result can only be self-casting nets. At this moment, the horned squid opened its mouth, and the surrounding sea suddenly sank, and the gluttonous fish entered its mouth and became a good meal for it!
The spikefin fish, which also live in the deep sea, are also "experts" who are proficient in this way. Its "fishing rod" is even more wonderful, because the dorsal fin bone line changes more, as if it is a series of fishing rods in the form of branches, and there is a small spike growing on the tip of each rod, and this "fish hook" expander, "bait", can "lure the enemy deeper" all day and night, because it can constantly fluoresce. The phototropism of some small fish simply cannot resist the temptation of "fluorescent expanders", and they have become the food in the mouth of the fin fish.
There are many more such examples. An interesting fish living in the Caribbean, it is only 15 centimeters long and has a white "bag" under the eyes that emits a white light. In the dark and boundless deep sea, it usually relies on the light emitted to attract and prey on small fish. And when it finds danger, it can also automatically turn off the light, just like a flashlight that can be automatically switched on and off, so it is called "Atlantic torch fish".
Due to the high efficiency with which deep-sea fish and other organisms change from chemical energy to light energy, it can reach almost 90%. Therefore, this phenomenon gives people a great enlightenment: people have not only successfully developed fluorescent lamps with high luminous efficiency, but also considered manufacturing a new light source that can provide safety for the lighting under the mine and avoid accidents such as gas explosions. The application of this kind of cold light undoubtedly has broad prospects, such as when removing magnetic mines, which can avoid magnetic mine explosions. Now, people have been able to initially use the method of mixing certain chemicals to obtain cold light similar to biological light. Many researchers are also continuing to delve into the mechanism of bioluminescence, hoping to draw some inspiration from it in order to create an efficient artificial cold light source. It seems that the days of large-scale use of cold light sources for lighting by human beings may not be far off. At that time, not only will there be a variety of low-cost cold light emitters, but also can decorate the cold light glow wall, which is really "night like day".
The deep sea is one of the largest treasure troves of biodiversity on Earth. At present, only about 1% of human understanding of the underwater world is known, and much less is known about deep-sea species and their living environments. The human exploitation of the deep sea has only just begun, and it has been proved that the species richness of the deep sea is far more than people think. This suggests that biological evolution has cleverly designed deep-sea fish and other animals to adapt well to the apparently unfavorable environment of the deep sea.
Regrettably, the world's largest ecosystem in the deep sea is currently under increasing threat, with the depletion of deep-sea fish and other marine animal resources, and the threat stems in large part from human activities, particularly overfishing. For example, overfishing and destructive fishing methods, particularly trawling operations, have led to a sharp decline in the populations of five deep-sea fish species, namely the deep-sea long-tailed cod, the North Atlantic long-tailed cod, the blue cod, the thorny eel and the spiny-tailed deep-sea ray, which have declined by 89 to 98 per cent in the five years from 1978 to 1994, and are on the verge of extinction, with promising prospects.
In the past, marine fisheries were mainly concentrated in shallow seas. After the sharp decline in shallow fish populations due to overfishing, people turned their fishing targets to the deep sea. In this regard, people must take timely and effective management measures, otherwise overfishing or destructive fishing methods will cause serious damage to deep-sea ecosystems with rich species, and the biodiversity of these ecosystems is much unknown to human beings and has great potential value.