Coelacanth is a “living fossil”; this amazing fish is older than dinosaurs. It has survived to this day, in the process of an incredibly long evolution, practically unchanged. It’s a pity, but anthropogenic influence is seriously decimating the population of the unique coelacanth fish. And this despite the fact that the species is not suitable for commercial catching and cultivation, and is not used for culinary purposes. And the ancient fish is being destroyed by human irresponsibility coupled with environmental degradation.
Description of the fish
Coelacanth is a marine tropical deep-sea fish.This is a lobe-finned fish, also called a coelacanth, belonging to the subclass Lobe-finned fish, which, in turn, belongs to the class Bony fish. That is, the skeleton is represented by bones, and not cartilage, as in cartilaginous species. Lobefins are an interesting subclass, the name of which is due to the fact that its representatives have fins of a specific shape, attached to a muscular base protruding from the body. These fish are also called fleshy-lobed and choanoid.
The species of coelacanth according to biological classification is described in detail in the table.
| Type | Chordata |
| Class | Bony fish |
| subclass | Lobe-finned (according to the outdated classification Lobe-finned) |
| squad | Coelacanths |
| family | Coelacanths |
| genus | Latimeria |
Coelacanth has a unique skeleton. It does not have a typical spinal column; instead, the supporting skeletal base is a flexible tube with thick walls, about 4 cm in diameter, which holds its shape thanks to its liquid contents. This variation of the spine should not be confused with the notochord, which is preserved in some fish called chordates, such as sturgeons.
The coelacanth's skull is also unique; it is represented by two bone plates that are held together by a joint and muscle attachment. Thanks to this structure, the fish is able to open its mouth unusually wide, not only lowering the lower jaw, but also raising the upper one. The fish searches for food using special sensory organs that emit electric currents.
Despite belonging to bony fish, coelacanth is to some extent similar to cartilaginous species. So, she has a similar digestive system and the same small brain volume. But cartilaginous species do not have a swim bladder, while coelacanths do, like all bony fish.
The older an individual coelacanth becomes, the more its brain tissue is replaced by fatty tissue. In the oldest individuals, the brain itself is only 3-5 g, and about 300 g is fat.
In appearance, coelacanth looks more like amphibians than fish. Particular similarities are noted with newts. Thus, the joint between the parts of the skull is characteristic of amphibians. There are dividing elements between the auditory organs and the braincase, between the respiratory organs and the eye recesses. The skull is widened at the back. The palate is covered with bony plates from which cone-shaped teeth grow. The structure of the gill plates is more reminiscent of the dental tissues of mammals. The lung tissue does not function, there are no nasal passages. However, despite the inability to breathe, the coelacanth is still a lungfish, since it has rudimentary lungs.
The pectoral and ventral fins are paired. The second ones are located almost at the cloaca itself. The reproductive and excretory openings are separated from the cloaca. The tail has an additional pair of fins and another rudimentary petal fin. The gills are four paired. The stomach of coelacanths is also unusual, equipped with a spiral valve, which is found only in rays and sharks.
Female coelacanths are larger than males. The first grow up to 2 m, the second - only up to 1.5 m. Adults weigh on average 100 kg. The body is covered with incredibly strong and large scales. The color of the fish is faded blue, sometimes acquiring brown tints. The body is covered with large light specks that camouflage the fish in its natural environment.
Historical reference
Representatives of the ancient species Latimeria are an intermediate link between fish and ancient amphibians that left the marine environment in Devon, that is, approximately 400 million years ago. Until relatively recently, biologists were sure that the coelacanth was extinct.But in 1938, in the waters near South Africa, fishermen caught a strange large fish.
This fish was seen by an employee of the South African Museum, Marjorie Courtenay-Latimer. The woman had no idea what kind of species it was; she had never seen such fish before. Then she turned to professor of ichthyology James Smith, who immediately realized that this was a real coelacanth. This discovery turned out to be one of the most significant in the history of biological science of the 20th century.
The coelacanth, caught and turned into a stuffed museum specimen, was named after a museum employee after the second part of her last name. Later this name was assigned to the entire species.
Before this discovery, scientists knew coelacanths only from fossilized remains. According to paleontological finds, coelacanths were a very common species approximately 300 million years ago. James Smith began looking for this fish in different waters to clarify its habitat. It is noteworthy that African fishermen caught coelacanths even before 1938, but simply did not pay attention to them, since they were not edible.
The second specimen of coelacanth was caught near the Comoros Islands only in 1952. By the beginning of the 1980s, about 70 individuals had already been caught. At first it was believed that the range of coelacanth covers only African waters. But in 1997, the same fish were discovered in Indonesia. And completely by accident. Biologist Mark Erdman, walking with his young wife through an Asian fish market, discovered a caught coelacanth on the counter. Coelacanth was also caught off the Kenyan coast, off the northern part of Sulawesi.
In the 2000s, it was possible to observe the life of two individuals from a bathyscaphe. Photographs of coelacanth in natural conditions were taken by the same Mark Erdman. But in general, catching coelacanths was a great success; these fish were rarely found, as they lived at considerable depths.For the same reason, the species is still little studied.
It is known that coelacanth is a relative of tetrapods. At first, scientists believed that it was the ancient coelacanths that became one of the ancestors of terrestrial four-legged animals. And all because of the unusual fins, reminiscent of the paws of amphibians. But after some time, scientists proved that the terrestrial fauna descended from another ancient group of lungfish. These fish, thanks to the connection of the swim bladder with the esophageal tube, survived in water with a low oxygen content, and then began to live outside water bodies altogether. And the coelacanths retained their intermediate appearance.
Habitat
Coelacanth lives in only two limited areas of the World Ocean: off the southern and eastern coasts of Africa, as well as in the Indonesia region.
The first variety is called Comorian, its population is more numerous, covering the coastal waters of Mozambique and South Africa, the island of Madagascar, and the Comoros archipelago. The second variety, discovered later and called menadoensis, is not so common, lives in the coastal waters of the island of Sulawesi. That is, the distance between the habitats exceeds 10,000 km. The populations are completely separate.
Lifestyle
Coelacanth is a nocturnal species. During the day, fish sit out in secluded places in the bottom zone. When night comes, fish swim out of their hiding places and begin to look for food. Coelacanths swim slowly, measuredly, saving strength. It is rare to escape from predators in the near-bottom area, within 3 m from the bottom, so the fish have nowhere to rush. And the coelacanth has few enemies; these are mainly large species of sharks. And coelacanths hunt small sharks themselves.
Representatives of the species almost never rise above 200 m from the sea surface. And even then, only at night, when they are active.In search of food, the coelacanth is able to travel several kilometers until dawn comes. They swim funny, moving their fins and legs like newts, but, contrary to popular belief, they do not know how to walk on the bottom. Coelacanths rarely resort to physical activity; more often they prefer to drift limply in the water column, obeying the currents. Fish use their fins more often as a rudder to adjust their spatial position than for swimming.
To maintain the viability of coelacanths, the temperature of sea water should not exceed +18°C. Already at +20°C the fish die.
Thanks to the unique shape and arrangement of the fins, the coelacanth can freeze in the water column in any spatial position: turning on its side, in a vertical direction with its head down or up. Not only does not a single cartilaginous fish, which is forced to move all the time due to the lack of a swim bladder, possess this ability, but even the majority of bony species cannot do this.
The fish remains in a vertical position for about 2 minutes. Scientists speculate that vertical freezing has something to do with the electricity emitted by the fish. One day, scientists in a submersible forced the coelacanth to take a vertical position by passing a current through its body. If the coelacanth senses danger, then it is capable of sharply rushing forward, intensively moving its strong and large caudal fin.
Coelacanths live in small flocks of up to 10 individuals. Coelacanths are considered long-livers; scientists believe that representatives of the species live up to 80 years. This longevity is due to a measured and calm life at considerable depth.
Nutrition
The sharp cone-shaped teeth of coelacanths indicate a predatory nature.The coelacanth detects the approach of its prey at a considerable distance through emitted electric fields, the reflected impulses of which are captured by special receptors on the fish’s body. Coelacanths hunt in schools.
Most common victims:
- cephalopods;
- small sharks;
- other fish;
- small benthic inhabitants.
Being a large fish, the coelacanth could easily hunt large fish. But coelacanths prefer to hunt as hassle-free, measured and leisurely as they live. They look for a victim that is not nimble, unable to resist or swim away quickly.
Coelacanth teeth are not adapted for chewing food. The fish simply grabs the victim with its teeth, and then does not swallow, but literally sucks it into itself, which is possible thanks to the unique jaw and digestive apparatus that the ancient bony fish has. With the help of such an apparatus, the coelacanth can suck in prey, even if it is hidden in bottom crevices and depressions.
Based on this, it is clear why there is a spiral valve in the coelacanth’s stomach. It increases the length of the digestive tract, making it sufficient for digesting whole swallowed prey. The leisurely behavior of the fish also becomes clear, because its body spends a lot of energy on the digestive process.
Reproduction and spawning
Female coelacanths become sexually mature only at 20 years of age. And spawning occurs once every few years. The female is fertilized internally, but scientists have not yet been able to observe the fertilization process. It was also not possible to establish where the young live. Probably, young individuals hide in caves, thereby ensuring a higher percentage of survival.
One thing scientists know for sure is that this ancient fish is viviparous. At first, scientists believed that coelacanths laid eggs. One day, a female was caught with supposedly eggs the size of tennis balls inside. Then another female was caught, whose body contained embryos approximately 30 cm in size with a yolk sac, which serves as a source of intrauterine nutrition. It turned out that the imaginary eggs are simply embryos at an early stage of development.
An interesting discovery by scientists indicates that coelacanth embryos are fed inside the mother not only with the contents of the yolk sacs, but also with nutrients coming from the mother’s blood through the placenta. One day, a pregnant female was caught and approximately 70 embryonic eggs were found in her body. Coelacanth cannot give birth to such a number of fry. Scientists noticed that some embryos were more developed, others were at the initial stage of development. And then the assumption arose that in coelacanths, like sharks, more developed embryos absorb their weaker brothers.
Types of fish
Based on their habitats, there are only two types of coelacanth:
- Comoran - Latimeria chalumnae - living off the African coast;
- Indonesian - Latimeria menadoensis - found off the Indonesian coast.
These are the only species of coelacanths that have survived to this day. It is believed that in prehistoric periods the coelacanth family included over 120 species.As a result of scientific research, it was possible to find out that the two presented species separated about 40 million years ago. Scientists insist that these are exactly two different species, although their structure is almost similar.
Security status
Coelacanth, as soon as it appeared in the lens of scientists, was recognized as a species on the verge of extinction, and therefore included in the international Red Book. According to the Convention on International Trade in Endangered Species of Wild Fauna and Flora CITES, coelacanth has a species status that is at the critically endangered level.
Today, only about 400 adult coelacanths live in the world's waters. Moreover, 300 of them belong to the Comorian population. Africans even gave the unusual fish a name - kombessa.
The numbers of the Comorian variety of the ancient species began to decline sharply in the 1980s and 1990s. There were several reasons for this. Firstly, the fish were often caught by African deep-fishermen. The caught fish died, but were not used as commercial fish. Secondly, in those years, the spinal tube of coelacanth was sold on the black market as a means of rejuvenation; for one individual they fetched from $5,000. Well, we should not forget about the deteriorating ecology, and coelacanths are extremely sensitive to water quality.
