Lungfish were found only in the last century. Until that moment, no one had seen them live. Representations about them were limited only to ancient remains found. Their structural features led to such an interesting name. Let’s see which fish are breathless and what is so special about it. The fact is that representatives of this class can breathe not only gills, but also lungs.
Who are Lungfish?
Representatives of this superorder of lobe-finned fish possess both gill and pulmonary respiration. Such is the peculiarity of their structure. In the modern world, the subclass Lenticular fish, representatives of which are divided into two orders - horn-shaped and bipedal, is quite rare. The individuals related to it live only in Africa, Australia and South America.
In addition to ordinary gills, they also have lungs (one or two), which are a modified swim bladder. Through its walls penetrated by capillaries, in fact, gas exchange occurs. Fish capture air for breathing by mouth, rising to the surface. In the atrium, they have a septum, which continues in the ventricle. Blood flows through the veins from the organs and enters the right side of the atrium, as well as the right side of the ventricle. Blood coming from the lung enters the left side of the heart. An interesting fact is that further oxygen-rich pulmonary blood goes mainly to those vessels that pass through the gills to the head and various organs. And the second part of it from the right side of the heart, also passing through the gills, is in the vessel leading to the lung. It turns out that oxygen-rich and poor blood is still partially mixed in the vessels and heart. So, we can talk about the primitive rudiments of two circles of blood circulation in double-breathing fish.
Ancient Lungfish
Lungfish are representatives of a very ancient group. Their remains are found among sediments of the Devonian period (Paleozoic era). For a fairly long time, such fish were known only from fossilized remains. And in 1835, it was discovered that the protopter living in Africa is a double-breathing fish.
The subclass of double-breathing fish, whose representatives have survived to this day, consists of only six species:
- The Australian Horned Tooth is a one-lung squad.
- American flake from the bipulmonary unit.
- Four varieties of Protopterus from Africa (two-lung).
Apparently, they all, together with their ancestors, belong to freshwater fish.
Australian horned tooth
Lungfish include Australian horned teeth. They are found in a very small area of the Mary and Burnett River Basin in northeast Australia. This is a large fish up to 175 centimeters long and weighing more than ten kilograms.
The large body of the horned tooth is flattened on the sides and covered with large scales. Large paired fins look like flippers. The color of the horned tooth's body varies from red-brown to bluish-gray, and the belly is certainly a light shade.
Fish lives in rivers with a slow course, where surface and underwater thickets are present. Every fifty minutes, the horned tooth rises to the surface and with a noise releases air from the lung. At the same time, he emits either a groan or a grunt, which is heard far enough. Having inhaled fresh air, the fish sank to the bottom again.
Habitat
The horned tooth mainly spends time at the bottom, lying on its belly or standing on the fins-like fins. To search for food, he begins to crawl slowly. The fish also swims extremely slowly. However, if she is frightened, she begins to quickly work her tail, thereby accelerating her movement.
During periods of drought, when the rivers are completely shallow, the cattails lie in the remaining water pits. In hot water, devoid of oxygen, the whole fish dies, and she herself turns into a stinking dirty slurry. In such conditions, only bipedal fish survive, representatives of which are able to breathe lightly. However, if the water evaporates completely, then the horned teeth still die, because, unlike their South American and African relatives, they do not know how to hibernate.
Fish spawning occurs during the rainy season when the rivers overflow with water. The roe-toothed lays large eggs on algae. After 12 days, larvae appear that are located at the bottom until the yolk sac is resorbed, sometimes moving slightly over insignificant distances.
It is believed that on the 14th day after the appearance of fry in the light, their lung begins to function. The chisels are very tasty, and catching them is very simple. This is what led to a sharp reduction in their numbers. Currently, they are under protection, in addition, attempts are being made to relocate them to other Australian reservoirs.
Protopters - African Lungs
Protopters also belong to double-breathing fish. They live in Africa and have filamentous fins. Of the four species living on the continent, the largest - the large protopter - reaches a length of more than one and a half meters. The average length of the fish is about thirty centimeters. Fish swim like eels, twisting the body. But filamentous fins help them move along the bottom. An interesting fact is that the skin of the fins is rich in receptors. As soon as the fin touches something edible, the fish immediately grabs its prey. Periodically, the protopter pops up and breathes in fresh air. Protopters live in the central regions of Africa. What places for life are breathing fish? Representatives of this species prefer rivers and lakes in swampy areas, which are flooded annually during rains and dry out during droughts. In the dry period, the water level drops from five to ten centimeters. At this time, the protopters begin to dig holes for themselves.
Fish by mouth absorbs the soil, and then grinds it and throws it out through the gills. The hole is a vertical passage, at the end of which there is a camera, where, in fact, is the protopter, bent in half and with his head out.
Until the water is completely dry, the fish rises to breathe. And then the liquid sludge is sucked into the hole, blocking the outlet. Then the protopter cannot get out. He just pokes his face in a cork from the sludge, lifting it. After drying, it becomes porous and passes oxygen, which allows the fish to survive while in hibernation.
Water in a hole gradually becomes very viscous due to mucus secreted by the protopter. The soil gradually dries out more and more, and the water level in the hole falls. As a result, the vertical stroke is filled with air. Bending over, the fish freezes in the lower chamber. A cocoon of mucus is formed around her body. It is in this state that the protopter expects a rainy period, which occurs only after 6 - 9 months.
Dry behavior of fish
Breathing fish are quite interesting in their behavior and living conditions. Representatives (photos are given in the article) of this group participated in laboratory studies. So, protopters were kept in hibernation for more than four years, and at the end of the research they woke up safely.
During hibernation, fish metabolism is greatly reduced. Nevertheless, in six months, protopters lose up to 20 percent of their mass. Energy enters the body due to the breakdown of muscle tissue, which is why ammonia accumulates in the body. In the active period of fish’s existence, it calmly goes outside, but during hibernation it turns into very toxic urea, the concentration of which is quite high. But body poisoning does not occur. How such stability arises is not yet clear.
With the beginning of the rainy season, a gradual soaking of the soil begins, water fills the hole, the protopter, breaking the cocoon, periodically protrudes its head and breathes in air. As soon as the water completely covers the bottom of the reservoir, the fish leaves the hole. After a month and a half, the protopters will begin the breeding season. At this time, the male digs a new norm in the thickets and lures the female there, which will lay up to 5 thousand eggs. And after 7 days, larvae will appear. And after 4 weeks, the fry begin to eat on their own and leave the mink. For a while they swim next to her, hiding at the slightest danger. Throughout this period, the male is always near the hole and protects it from enemies.
Protopter dark
Considering the topic "Breathing fish: representatives, names", it is necessary to recall another representative of this class - the protopter dark. It lives in the Congo and Ogove river basins, preferring wetlands in which the underground water level is maintained even during a drought. When the water begins to decrease in the river, the fish burrow into the bottom mud, reaching the underground water. There, the protopter spends the entire dry period, while not creating a cocoon; periodically it rises to the surface to breathe air.
The fish hole is an inclined course and a chamber at the end. Fishermen say that such a shelter serves the protopter for five to ten years. In the same hole spawning occurs. Males prepare for this event in advance, building around a hill of mud, which can reach one meter in height.
Lungfish, briefly described by us in the article, always attracted the attention of scientists, they are so unusual and interesting. Protopters are interested in researchers of sleeping pills. The biochemists of Sweden and England tried to isolate substances from fish organisms that enable them to hibernate. And here's what is interesting: when the extract from the brain of sleeping fish was injected into the blood of laboratory rats, the body temperature of the subjects began to drop sharply, they fell asleep very quickly, almost instantly. The dream lasted up to 18 hours. After waking up, no signs of artificial sleep were found in rats. The substance did not give any adverse reactions.
American flake, or lepidosiren
The considered examples of double-breathing fish clearly demonstrate their adaptability to completely unsuitable living conditions. And, nevertheless, even under such circumstances, due to the ability to breathe in two ways, the fish feel great.
The class Bicentennial fish, the representatives of which were considered above by us, also includes American scalefish, which lives in the Amazon. The length of the fish reaches 1.2 meters. It lives, as a rule, in temporary bodies of water that floods during rains or spills. Lepidoptera feed on various animal foods, mainly mollusks. Perhaps they eat plant foods. When the pond dries, the fish are buried at the bottom of the hole and plugged with a cork. However, they do not form cocoons. Sleeping fish is surrounded by mucus and moistened with groundwater. The basis of energy metabolism, unlike the protopter, is the accumulated fat.
A couple of weeks after the flooding of the reservoir, American flake begins to multiply. The male pulls out a hole that can reach one and a half meters in length. In its very depths, he drags grass and leaves onto which females toss eggs. The male remains in the hole and protects the juvenile. During this period, growths appear on his ventral fins. Some ichthyologists say these are temporary external gills for extra breathing. Others believe that with the help of these growths, the fish partially gives off oxygen taken when it was raised to the surface of the reservoir. True or not, it is not known exactly. However, after the breeding season, outgrowths disappear.
Lungfish. Representatives: coelacanth
Another representative of double-breathing fish is coelacanth (coelacanth). They are very few in number and covered in a mysterious veil. They live near the Comoros. However, local fishermen produced them in the entire history of no more than two hundred pieces. The length of the fish is from 43 to 180 centimeters, and the weight reaches 95 kg. An interesting fact is that all coelacanths were caught from September to April, and in the dark. Fishermen caught them on bait from squid or pieces of fish. Fishing rods were cast at decent depths (from 150 to 400 meters). Attempts were made to trap coelacanth by traps or a trawl, but none of this came of it. Perhaps this is due to the difficult topography of fish habitats.
Coelacanth is a double-breathing fish. It has a rather interesting structure. For example, she has no vertebrae. The spine is formed by an elastic thick rod. The swim bladder, which serves as a lung for breeders, is reduced to a small tube. The eyes of coelacanth are adapted to dwell in the dark. The biology of coelacanth has been studied very little. In general, bipedal fish are very interesting in terms of their habitat. Representatives (a list of them was given by us in the article) of this class are quite unique. There are not many left on earth. Moreover, due to their good taste, they are still being exterminated.
But as for coelacanth, then catching it is not so simple. Scientists suggest that it lives among the basalt rocks of the Comorian rocks at great depths. Those rare specimens that fell into the fishing rods of the fishermen, of course, were subjected to close inspection. So, in their stomachs were found the remains of deep-sea fish living at a depth of 500 to a thousand meters. Most likely, coelacanth leads a sedentary life, although, as we already talked about double-breathing fish, they can make sharp throws, thanks to their strong tail. Moving paired fins help them squeeze through clefts of rocks. Coelacanth does not tolerate bright sunlight and high temperature of the surface layers of water.
