Sharks are predator fish, dangerous and aggressive inhabitants of the ocean, the oldest known animals. This is considered to be, and millions of people believe in this, drawing knowledge of these unique creatures from Hollywood horror thrillers. Let us see what we know about these amazing creatures, which appeared much earlier than all the civilizations of the world and perfectly adapted to modern life. What is a shark? Is it a fish or a mammal?
All scientific and encyclopedic publications claim that sharks are cartilaginous fish, i.e., they have absolutely no bony tissues in their bodies, which makes them stand out from their modern habitats. Together with the absence of gill covers and the characteristics of the structure of scales, the cartilage ostyak indicates the primitiveness of the organization of the species, or rather its ancient origin: it is known that 400 million years ago these fish were already swimming in the world's oceans. Despite this, sharks are one of the most advanced species of carnivorous ocean fish. For a long time, adapting to the ever-changing environment, they adapted superbly and now get along perfectly with modern bony fishes and marine mammals, not yielding to them either in speed, or in dexterity, or in hunting skills. The list of sharks includes more than 400 species that are polarly different: from the shallowest of the deep, barely growing to 17-20 cm, to the giant - the whale shark, a huge 20-meter high-tonnage individual.
An important difference from bony fish are the methods of reproduction. Some species of sharks are viviparous, i.e. give birth to live young. Some lay eggs protected by a dense cornea. Not all secrets of their life are open: there are species, the secrets of the reproduction of the offspring of which are still behind seven seals. Therefore, the question often arises: "Is a shark a fish or a mammal?"
Features of the form
The cartilaginous skeleton and the absence of bones are the main signs of the attitude of these fish to a group of animals of a primitive organization. But, as mentioned above, this does not prevent the shark from dwelling in almost all the oceans of the planet, having long won fame as the most dangerous and aggressive predator. In addition, nature has taken care of the protection of this amazing animal. It is difficult to find something more protective than the scales that a shark possesses. Located from the head to the tail, it feels like a satin finish to the touch, but you should not hold your hand in the opposite direction - from tail to head: sharp teeth pierce the skin. Coarse sandpaper compared to this perfect protection is a weak resemblance.
Consider the device scales. Each scale of cartilaginous fish is supplied with a small thorn with a pointed back. From above the spike is covered with a layer of the strongest enamel, and its expanding base is spliced with the skin of fish. In the cavity of this process are the blood vessels and nerve branches. The size of the scales on the body of fish is different: the largest fish is located on the head, the thorns in the mouth of the shark, having somewhat transformed, ceased to be the protection of the skin and turned into a sharp and extremely dangerous instrument of attack - magnificent teeth.
Being modified scales, shark's teeth are arranged in strict staggered order, in several rows. During the life of the predator, the teeth grow constantly, and when one row is abraded, new ones located in the depths of the mouth germinate. Shark teeth do not serve to chew food. She does not know how to do this. Their main purpose is to hold the prey, tear it apart to swallow it without interference. Different types of sharks have different tooth shape, which is dictated by lifestyle features. Bottom, feeding on crustaceans in hard shell, have flat, ribbed teeth that can crush lime defenses. Predator fish have long, sharp teeth to grab moving prey, or wide, with a serrated edge, designed to tear the meat of a large prey. Plankton sharks have practically no need for teeth, they are small in these species, barely reaching 3-5 mm.
Another feature of cartilaginous fish is the absence of gill covers. Their role is performed by 5-7 gill slits located behind the head, the number of which is determined by the type of sharks, and the presence is a distinctive feature. However, like all fish, these predators, getting oxygen from water, pass it through the gills. The presence of the respiratory system, characteristic of waterfowl, gives an exhaustive answer to the question: "Is a shark a fish or a mammal?"
Amazing Abilities: Smell, Electro-Receptor Apparatus and Sideline System
It is impossible to overestimate the possibility of smell in sharks. This is one of the most advanced basic sensory systems. Experiments have shown not only the high sensitivity of fish to odors, but truly amazing. The shark can catch the smell of blood diluted in water at a ratio of 1: 1,000,000, and constantly use the smell when looking for prey or partners for breeding in the mating season. In determining the location of the object, probably, in addition to a highly developed sense of smell, other organs and systems are also involved: hearing, taste buds, as well as the lateral line located on the surface of the fish’s body, which can sense both insignificantly weak mechanical movements and even the smallest low-frequency oscillations in water. , and playing an important role in hunting, communicating with fellows and orienteering.
There are unproven scientific assumptions about the ability of these predators to catch odors spread through the air, which led the researchers to the strange behavior of the white shark. She often raises her face above the surface of the water surface, as if sniffing.
The unique ability of sharks to detect a victim by the movements of the respiratory and cardiac muscles, electric fields with negligible voltage, has been scientifically proven. Long-term observation of the migration of some species over fairly long distances in a straight line made it possible to identify the possibility of their orientation in the Earth’s magnetic field.
The uniqueness of this representative of the fauna once again underlines the special structure of the eye, which provides both protection from external stimuli and excellent visual acuity. Features of the device of the organ of vision of the shark are in the presence of a blinking century, closing the eye at the time of the attack on the victim, thereby protecting it from damage. In fairness, it should be noted that not all species have eyelids. These individuals roll their eyes when attacking the victim.
Moreover, the shark's eye has a special reflective layer located behind the retina, which enhances the sensitivity of this organ and significantly increases visual acuity even in low light. Today, it does not require proof of the fact that the vision of some species of these fish is many times greater than that of humans.
Unlike most teleost fishes, which produce millions of eggs, reproduction of their own kind in sharks aims more at quality than at quantity. Characteristic features of cartilaginous fish — internal fertilization, widespread egg production, and live birth, significantly reduce the mortality of offspring, allowing for a high survival rate and lower fecundity.
Depending on the species, sharks can be egg-laying, viviparous and oviparous. Oviparous is almost a third of all species. After internal fertilization, the female lays eggs covered with a gelatinous protein layer, protected on top of it with a hard shell, which protects the contents from dehydration and external damage. The supply of nutrients in the egg is enormous, it does not dry out during the full development of the embryo, which, it should be noted, is quite long. As a rule, a small number of eggs are simultaneously laid: from 1 to 12. The only exception is the polar shark, which lays up to 500 eggs up to 8 cm long. The slow development of the embryo pays off handsomely - the hatched small shark is perfectly adapted to life and differs from an adult only in size.
A distinctive feature of egg-breeding is that, having hatched from fertilized eggs, the young remain in the mother's oviduct for some time, being born developed and perfectly adapted to independent living. Information on the timing of gestation of offspring in the egg-breeding species requires clarification. According to some data, this period ranges from several months to two years, like that of a barbed shark, which is a record among all vertebrates.
In the womb of viviparous individuals up to 30-80 embryos can develop simultaneously. Regardless of the type of shark and mode of reproduction, all are distinguished by the reproduction of small but capable of independent offspring.
Most of these fish are common in the oceans and seas, inhabiting the water column from the surface to a depth of two kilometers, and are classified as true predators. But there are exceptions in this family: the bigmouth, giant, whale and some other shark species are filter feeders, feeding on plankton, small fish and squid.
The whale and giant sharks are considered the largest, reaching a length of 20 and 15 meters respectively. Being planktonic fishes, they slowly move, having opened a mouth, in the center of clusters of plankton, driving water through the gill openings with special outgrowths-plates, filtering out a huge amount of water and extracting from it all living organisms larger than 2 mm.
There is very little information about the reproduction of plankton species. Thus, the life of a giant shark is completely unknown. Whale - egg-laying. The eggs laid by her reach quite impressive sizes: the length can be 0.7 m, width - 0.4 m. Despite the enormous size, the planktonic shark fish, the photo of which is presented in this article, is completely non-aggressive and very slow.
The world of sharks is amazing and diverse. Some of them are benthic and feed on crustaceans and invertebrates, such as small cats, no larger than 1 meter in length. The object of the trade is the prickly quark shark, the photo of which is also presented in the article.
Katran, having a wide distribution, is the only species living in the Black Sea. This sea shark is extremely cold-loving and does not enjoy the warm waters. Perhaps this explains the fact that the Black Sea quatane rarely reaches 1 meter in length, although in the North Sea the size of this fish is 1.5-2 m. Thorny sharks practically do not rise to the surface of the water and do not approach the shore. They live at a sufficient depth, falling into large shoals. Katrans feed on bottom invertebrates and bottom fish - flounder, whiting, successfully hunt shoals of Hamsa.
It is striking that the Katran is an egg-bearing fish, the pregnancy of which lasts an incredibly long time - up to 2 years. Sharklets are born absolutely ready for the predator's adult life. Inaccessible to humans, protected and cautious, they grow to adulthood without any problems. These sharks in the sea are safe for humans. They never swim close to the swimmers. The incredible system of highly developed sense of smell and the feeling of the slightest frequency oscillations helps the katran to avoid encounters with people. Flocks of this fish approach the coast in late autumn. Then begins the fishing season. The second name of the shark - prickly - given to the katranam for good reason This fish is able to deliver a lot of trouble when it gets out of the trawl. It possesses not only strong scales, but also sharp spines in front of the dorsal fins, at the base of which are poison glands. In contact with them you can get a portion of the poison, though not fatal, but bringing certain inconveniences. The Atlantic Ocean catches most of its catch: sometimes it is possible to catch up to 20 thousand fish in one notice.
The prickly shark is not just a tasty fish, it is very gentle and, of course, healthy. In the skillful hands of a good cook, the meat of the katran turns into magnificent delicacies, wholesome and delicious dishes. An indispensable rule in the preparation of shark meat is the mandatory discharge of blood immediately after the fish are caught. It has a high concentration of ammonia. If you do not get rid of the blood, the product will be hopelessly spoiled. The advantage of these dishes is the fact that there are no bones in their meat, because this fish is cartilaginous.
The skin of Katrans is also appreciated. The abrasive properties of the cuticles are always used by craftsmen in many industries: from carpenters, cabinetmakers and carpenters to furriers.
Fully justifying the reputation of the storm of tropical seas, the tiger shark, yielding white in the number of recorded attacks on humans, significantly exceeds its percentage of deaths after meeting with it. The name of the shark is determined by its external features. The tiger shark (or sea tiger) is so named because of the dark transverse stripes on the gray, brown-gray or greenish background of the body, which eventually turn pale. Preferring shallow waters, these sharks rarely fall below 300 meters, the cold waters do not attract them at all. The outstanding size of the fish - 7-8 meters in length and weight about a ton - put it in a number of the largest species. The streamlined body shape with a large head, a blunt snout and 5 gill slits, as well as a large maw with jaws, equipped with 280-300 flat, scraper-shaped teeth with a notch, and a well-developed upper lobe of the caudal fin — this is an incomplete portrait of this dangerous fish.
Sea tigers are tied to the chosen places, they do not like to leave the limits of their own residence. Being solitary predators, tiger sharks sometimes come together in groups, if there is enough food. But most often they patrol their area one by one.
The diet of these predators is made by pinnipeds mammals, dolphins, fish, waterfowl and even small representatives of their own species. They are so omnivorous that the contents of their stomachs, presenting a set of objects that are far from organic food, surprises researchers. For their exorbitant omnivorous nature, tiger sharks received the mark of “sea scavengers”. But more than relevant for them is the ability to turn the stomach through the mouth for rinsing in water, allowing you to get rid of completely indigestible objects such as banks, bags, various debris.
This dangerous shark belongs to the egg-breeding, bearing its offspring for 14-16 months and giving birth to up to 80 sharks in the litter, each up to half a meter in size.
Great White Shark
An exceptionally large aggressive predator - the white shark or karcharodon, which has long and firmly maintained the sad primacy of the number of attacks on people, is found in the surface waters of all the oceans of the Earth, except the Arctic, preferring a temperate and warm climate. It does not occur in cold waters, and also does not live in light-salted or desalinated seas. For example, in the Black Sea karkharodon does not appear. Most likely to meet with large white sharks on the coast of California, near the Mexican island of Guadeloupe, in the Mediterranean and Adriatic seas, off the coast of New Zealand, where they can swim in small flocks. The areas of the seas, where sea lions or seals are abundant, are especially loved by these predators. For a long time, there was an opinion about the constant coastal existence of white sharks, however, it was proved that fish migrate from the coast of California to African latitudes, swimming more than 20 thousand km in a year.
Being the largest modern predator (some specimens reach a length of more than 10 meters with a body weight of up to 3.5 tons), the white shark does not give the victim any chance of escape. This species owes its name to the color of the abdominal part - light or dirty-white. Its dorsal part is of darker tones: gray, greenish. Like all shark species, the white one does not have an air bubble, which explains the constant movement of the fish.
She treats food more biasedly than her tiger sister. The little shark eats medium-sized fish, mammals. Grown-up carcharodons hunt seals, dolphins, large fish and smaller species of the species. Adults do not avoid young or sick whales, often performing outstanding tactical moves during an attack, which only confirms their intellectual abilities. This dangerous shark has long proved that any prey is in the teeth.
Little information is available on the reproduction of offspring. As well as many species, they are egg-breeding with gestation period of 11 months, at the end of which 1-2 pups adapted for independent life appear. Today, the population of white sharks is rapidly decreasing, and there are no more than 3,500 of them worldwide. View listed in the Red Book.
Акулы в океане – зрелище завораживающее и отпугивающее одновременно. Оно способно и восхитить, и повергнуть в шок. Кто видел не только фото больших акул, но и стаю белых охотников воочию, не забудет этого никогда. Ведь даже картины с изображениями хищных рыб будоражат воображение. Мир акул – удивительный, фантастический и опасный. The most ancient creature and modern cruel predator get along in a unique animal, attracting attention, again and again raising the question: "Is a shark a fish or a mammal?"
Shark business got to the dolphins
Perhaps those who claim are right: the human ancestor is no monkey, but a dolphin. Our bodies are too similar, even the body temperature is almost the same. This is probably why dolphins are of great interest to ichthyologists.
Explore them in their natural habitat and in captivity. Pinnipeds feel good in the pools, of course, if the conditions of detention are normal. In nature, dolphins have no enemies, except sharks. And the dolphin does not expect any bad things from a man. How.
According to advertising, this is not a cheap remedy that can cure even the most severe cases of cancer. In our country, shark cartilage tests were not carried out, somehow, apparently, not before. But similar tests were carried out in 1998 in the United States.
In the November issue of the Journal of Clinical Oncology, American scientists published disappointing test results for cartilage manufacturers.
According to estimates of American physicians, shark cartilage has been used to treat 50,000 Americans already.
Sharks in Vladivostok
In Vladivostok, in the area of Russky Island, a flock of large sharks was found, in the same part of the Sea of Japan, where sharks have recently attacked people twice. On the evening of August 17, the shark attacked the resting man, who lost the hands of both hands. The next day, a shark attacked a 16-year-old, bending his legs. Fortunately, the doctors said that the victim’s legs would be saved.
"The Commission for the Prevention and Elimination of Emergencies of Primorsky Krai strongly recommends that residents and.
Nobody knows why the 200 grind jumped onto the land.
Dolphins are dying on the Australian beach
On the Australian coast again state of emergency. Nearly 200 grind — whales that look more like dolphins — night out on the shore of Tasmania’s King Island. Many of them have already died.
According to Sky News channel, rescuers and volunteers counted 194 grinds and several ordinary dolphins on the shore. Among them, only 54 grinds and seven dolphins were alive, with whom.
Dolphins call each other by name.
Stephanie King of the University of St. Andrews (United Kingdom) and her colleagues observed 179 pairs of bottlenose dolphins off the coast of Florida from 1988 to 2004. Ten of them copied each other's characteristic “whistle”, with which the dolphins “presented” to the interlocutor.
This has never been fixed.
They called each other by name (if I may say so) only members of pairs consisting of mother and baby or adult individuals who travel and hunt together.
Amazing sharks stomachs
10 of the most unusual finds in the stomachs of sharks:
1. In 1821, the newspaper told about a sailor who tried unsuccessfully to fish for metal dollars instead of bait. "Four days later, at a distance of 300 miles, his comrades caught a shark and a dolphin, in the stomachs of which three hooks with dollars were discovered," the publication said.
2. One sheep, a head and legs of a lamb, a horse-leg crab and some mysterious "sea owl" - this is an inventory of the contents of the shark's stomach caught in 1823.
Another civilization: dolphins - our brothers in mind?
Perhaps the first person to ignite public interest in "intellectuals of the sea", as marine biologists like to call dolphins, was the American neurophysiologist John Cunningam Lilly. He announced himself in the science of cetaceans as a whole cascade of amazing discoveries.
One of Lilly's books, The Man and the Dolphin, was translated into Russian.
The dolphin addiction of a neurophysiologist was influenced by the size and weight of the brains of these animals: in an adult dolphin a bottle of afalfin the brain weighs 1,700 grams, that is, 350.
Differences sharks from animals - breathing and blood flow
The main similarity of sharks with fish is breathing through the gills. No mammal has gills in adulthood. The blood from the heart goes to the gills, it is enriched with oxygen and is carried by the circulatory system throughout the body.
And here we are confronted with the first difference. What is it?
For the movement of such a huge mass with such a high speed there is not enough two-chamber heart. And muscles come to the aid of these predators. We encounter a similar system, getting acquainted with the venous circulation of a person, for example.
In order to return blood to the heart through the veins, which, unlike arteries, have less developed muscle fibers in the walls, skeletal muscle contractions are necessary. We see the same thing with sharks.
Watch the video - Shark circulatory system:
Here we find another difference between sea predators and other fish. The large muscles of sharks are very densely entwined with a network of blood vessels. These muscles, with their contractions, help the blood to return to the heart, since the pressure created by the heart alone is not enough.
In the process of movement, the muscles of the musculoskeletal system produce heat and give it to the vessels, so that the blood of sharks is warmer than their environment. The temperature difference can reach 10 degrees.
But this is not characteristic of all sharks, but only for the great white, blue shark, mako shark and some others. However, even these sharks are considered cold-blooded.
Watch the video - Shark Breath:
Sharks, again, unlike other fish, do not have a swim bladder. Only sand sharks are happy owners of an air pocket in which there is air. Due to the lack of a swim bladder, the process of lowering to a depth and rising to the surface is governed by movement. Some buoyancy sharks gives a huge liver, filled with fat.
So the movement of the shark is vital, and that is why it almost never sleeps. And if she decides to rest, it is only in a place where there are strong currents providing the gills, and accordingly the whole body, with a constant supply of oxygen.
Reproduction - the difference of sharks from animals and fish
One of the main distinguishing features of sharks, which separate them from fish, is internal fertilization. This type of fertilization can be found only in guppies, swordtails, and of two or three other bony fish.
The posterior part of the ventral fin is modified into two organs, called pterygopodia. According to one of them, at the moment of fertilization, the sperm enters the female's cloaca.
In egg-laying sharks, in the process of formation, the egg passes through special glands that supply it with a protein shell and a hard shell (often with special outgrowths). By the way - the eggs of sharks have a large supply of nutrients necessary for the development of the embryo.
It is a little like animals, rather birds, isn’t it?
Watch the video - Shark Egg:
There are, however, as we have already mentioned, sharks, which are similar in breeding style to animals. These are viviparous sharks. These sharks have an extended portion of the oviduct, a kind of "womb" - the chamber in which fertilized oocytes develop.
Moreover, the development of the embryo occurs first due to its own reserves of nutrients, and over time, between the growing baby and the placenta of the mother there is contact, through which nutrients come directly from the mother's body.
Sharks are smarter than animals
But the main difference between a shark and other fish is its brain. The ratio of body weight to brain mass is the same as in some birds and even mammals. Some scientists believe that sharks are easier to learn than rabbits and cats and remember the information obtained in the process of learning longer.
So do not treat sharks only as primitive "killer cars".
They still have a lot of things to tell us about, and they certainly cannot be called primitive, because they have perfectly adapted themselves to existence in the ecological niche from which the "King of Nature" is trying to oust them.