Sharks are fish-predators, dangerous and aggressive inhabitants of the ocean, the oldest known animals. So it is commonly believed, and millions of people believe in this knowledge of these unique creatures from Hollywood thriller thrillers. We will understand what we know about these amazing creatures that appeared much earlier than all civilizations of the world and perfectly adapted in modern life. What is a shark? Is it a fish or a mammal?
The Amazing Fish
All scientific and encyclopedic publications claim that sharks are cartilaginous fishes, that is, they have absolutely no bone tissues in their body, which strikingly distinguishes them from their modern counterparts in their habitat. Together with the absence of gill covers and features of the structure of the scales, the cartilaginous Ostyak indicates the primitiveness of the species organization, or rather its ancient origin: it is known that 400 million years ago these fish already sailed 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 constantly changing environment, they perfectly adapted and now perfectly coexist with modern bony fish and marine mammals, not yielding to them in speed, agility, or hunting skills. The list of sharks includes more than 400 species, polar different: from the smallest deep-sea, barely growing to 17-20 cm, to the giant - a whale shark, a huge 20-meter multitone specimen.
An important difference from bony fish are the ways of reproduction. Some species of sharks are viviparous, that is, they give birth to live cubs. Some lay eggs protected by a dense cornea. Far from all the secrets of their life are open: there are species, the secrets of reproduction of the offspring of which are still behind seven seals. Therefore, so often the question arises: "Is the shark a fish or a mammal?"
Features of the view
The cartilaginous skeleton and the absence of bones are the main signs of the relationship of these fish to the group of animals of a primitive organization. But, as mentioned above, this does not prevent the shark from inhabiting practically all the oceans of the planet, having long been known as the most dangerous and aggressive predator. In addition, nature has taken care of protecting this amazing animal. It is difficult to find something more protective than scales that a shark possesses. Located from the head to the tail, to the touch it resembles a satin finish, but it is not worthwhile to hold the hand in the opposite direction - from the tail to the head: sharp teeth will vop'yutsya in the skin. Coarse-grained sandpaper in comparison with this perfect protection is a weak likeness.
Consider the device of scales. Each scaly cartilaginous fish is equipped with a small spine with a rearward pointed point. From above the thorn is covered with a layer of strong enamel, and its expanding base is fused with the skin of the fish. In the cavity of this outgrowth there are blood vessels and nerve branches. The size of the scales over the body of the fish is different: the largest is located on the head, the thorns in the mouth of the shark, somewhat transformed, ceased to be the protection of the skin and turned into an acute and extremely dangerous instrument of attack - gorgeous teeth.
The main weapon
As a modified scales, the teeth of the shark are located in a strictly staggered order, in several rows. Throughout the life of the predator, teeth grow constantly, and when one row of abrasion grows new, located in the depth of the mouth. Do not shark teeth to chew food. She can not do this. Their main purpose is to keep prey, tear it apart, to swallow without interference. Different kinds of sharks have a different shape of teeth, which is dictated by the peculiarities of the way of life. Bottoms that feed on crustaceans in a solid shell have flat teeth with a ribbed surface, capable of breaking lime protection. Predator fish have long sharp teeth to grab moving prey, or wide with a jagged edge, designed to tear the meat of a large victim. In plankton sharks, there is practically no need for teeth, they are small in these species, hardly reaching 3-5 mm.
Another feature of cartilaginous fish is the absence of gill covers. Their role is played by 5-7 gill slits behind the head, the number of which is determined by the species of sharks, and the presence is a distinctive feature. However, like all fish, these predators, getting oxygen from the water, let it through the gills. The presence of a respiratory system, characteristic of waterfowl, gives an exhaustive answer to the question: "Is the shark a fish or a mammal?"
Amazing abilities: the sense of smell, the electroreceptor apparatus and the system of the lateral line
It is impossible to overestimate the possibility of smelling in sharks. This is one of the most perfect 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 uses the sense of smell when searching for prey or breeding partners during the breeding season. In determining the location of the object, in addition to highly developed olfaction, other organs and systems are also involved: ear, taste buds, and also a lateral line located on the surface of the fish body, capable of feeling both negligible mechanical movements and the slightest low-frequency fluctuations in the water , And plays an important role in hunting, communicating with fellows and orienting.
There are still unproven scientific assumptions about the ability of these predators to catch the smells spread by air, which led scientists to the strange behavior of the white shark. She often raises her muzzle over the surface of the watery surface, as if sniffing.
Scientifically proven the unique ability of sharks to detect a victim by the movements of the respiratory and cardiac muscles created by it, to electric fields with negligible stress. Long-term observation of the migration of some species over sufficiently long distances along a straight line made it possible to identify the possibility of their orientation along the magnetic field of the Earth.
The uniqueness of this representative of the fauna once again emphasizes 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 a shark consist in the presence of a blinking century, which closes the eye at the moment of attack on the victim, thereby protecting it from damage. For the sake of justice, it should be noted that not all species have eyelids. These individuals roll their eyes when attacking the victim.
Moreover, the eye of the shark has a special reflective layer located behind the retina, which helps to increase the sensitivity of this organ and significantly increases visual acuity even in low light conditions. Today, the circumstance that the sight of some species of these fish repeatedly exceeds the human one no longer requires proof.
Reproduction of sharks
Unlike most bony fishes producing millions of eggs, the reproduction of their kind in sharks is aimed at quality rather than quantity. The characteristic features of cartilaginous fishes - internal fertilization, widespread egg production and live birth, significantly reduce the mortality of offspring, allowing for a high survival rate and lower fertility.
Depending on the species, sharks can be oviparous, viviparous and ovovivorous. Oviparous is almost one third of all species. After internal fertilization, the female lays eggs covered with proteinaceous gelatinous layer, protected over it with a hard shell, protecting the contents from dehydration and external damage. The stock of nutrients in the egg is colossal, 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 is deposited simultaneously: from 1 to 12. The only exception is a polar shark, laying up to 500 eggs up to 8 cm long. Slow embryo development pays off a hundredfold - a hatched small shark is perfectly adapted to life and differs from an adult only in size.
A distinctive feature of egg-planting is that, hatching from fertilized eggs, the young remain in the mother's oviduct for some time, being born advanced and perfectly adapted to independent existence. Information on the timing of gestation of offspring in egg-living species requires clarification. According to some reports, this period ranges from a few months to two years, like a barbed shark, which is a record among all vertebrates.
Up to 30-80 embryos can develop simultaneously in the womb of viviparous individuals. Regardless of the type of shark and the method of reproduction, everyone is distinguished by the reproduction of a small but capable offspring of an independent life.
Most of these fish are distributed in the oceans and seas, inhabited in the thickness of water from the surface to a depth of 2 km, and are classified as true predators. But in this family there are exceptions: the giant, giant, whale and some other kinds of sharks are filterers, feeding on plankton, small fishes and squid.
The largest are the whale and giant sharks, reaching a length of 20 and 15 meters, respectively. Being plankton fish, they slowly move, opening the mouth, in the center of the plankton accumulations, driving water through the gill openings with special outgrowths-plates, filtering out a huge volume of water and extracting from it all living organisms larger than 2 mm.
It is about the reproduction of plankton species that very little is known. So, absolutely unknown yet is the life of a giant shark. Whale - oviparous. The eggs laid by her reach very impressive sizes: the length can be 0.7 m, width - 0.4 m. Despite the huge size, the plankton-fish shark, the photo of which is presented in this article, is absolutely not aggressive and very slow.
The world of sharks is amazing and diverse. Some of them lead a bottom way of life and eat crustaceans and invertebrates, such as small felines, no more than 1 meter in length. The object of the fishery is the prickly shark-katran, a photo of which is also presented in the article.
Katran, being widely distributed, is the only species inhabiting the Black Sea. This sea shark is extremely cold-loving and does not favor warm water. Perhaps this explains the fact that the Black Sea Katran seldom reaches 1 meter in length, although in the North Sea the size of this fish is 1.5-2 m. The spiny sharks practically do not rise to the surface of the water and do not approach the shore. They live at a sufficient depth, straying into large jambs. The cathars feed on bottom invertebrates and bottom fish - flounder, marmalade, successfully hunt for anchovies of anchovy.
It's amazing that Katran is an egg-eating fish, whose pregnancy lasts incredibly long - up to 2 years. Sharks are born absolutely ready for adult life predator. Inaccessible to humans, protected and cautious, they grow to an adult state without any problems. These sharks in the sea are safe for humans. They never swim close to the bathing. An incredible system of highly developed sense of smell and a sense of the slightest frequency fluctuations helps the katran to avoid meeting people.
The prickly shark is not just a tasty fish, it is very tender and certainly useful. In the skilful hands of a good cook, the meat of katrana turns into magnificent delicacies, useful and delicious dishes. An indispensable rule in the preparation of shark meat is the mandatory draining of blood immediately after the fish was caught. It has a large concentration of ammonia. If you do not get rid of blood, the product will be hopelessly corrupted. The advantage of such dishes is the fact that their meat has no bones, because this fish is cartilaginous.
The skins of cathars are also prized. The abrasive properties of the skins were always used by masters of many industries: from carpenters, cabinetmakers and joiners to furriers.
Fully justifying the reputation of thunderstorms of tropical seas, the tiger shark, yielding to white in the number of recorded attacks on humans, significantly exceeds it in the percentage of deaths after meeting with it. The name of the shark determines its external features. The tiger shark (or sea tiger) is so named because of the dark transverse bands on the gray, brownish-gray or greenish background of the body, which eventually turn pale. Preferring shallow water, these sharks rarely fall below 300 meters, cold waters do not attract them at all. Outstanding fish sizes - 7-8 meters in length and weight about a ton - put it in a row of the largest species. A streamlined body shape with a large head, blunt snout and 5 gill slits, and a large mouth with jaws equipped with 280-300 flat scraped teeth, and a well developed upper lobe of the caudal fin-that's the incomplete portrait of this dangerous fish.
Marine tigers are tied to their favorite places, they do not like to leave their own boundaries. Being lone predators, tiger sharks sometimes get into groups if there is enough food. But most often they patrol their area one by one.
Rats of these predators are pinniped mammals, dolphins, fish, waterfowl and even small representatives of their own species. They are so omnivorous that the contents of their stomachs, representing a set of objects far from organic food, surprises the researchers. For their excessive omnivor, tiger sharks have been branded as "marine scavengers". But more than actual for them is the ability through the mouth to turn the stomach to rinse in water, allowing you to get rid of completely indigestible objects, such as cans, bags, various rubbish.
This dangerous shark refers to egg-living animals, breeding their offspring for 14-16 months and giving birth in a litter to 80 sharks, up to half a meter in size.
Great White Shark
An exceptionally large aggressive predator - a white shark or carcharhodon, long and firmly holding a sad superiority in the number of attacks on humans, occurs in the surface waters of all the oceans of the Earth, except for the Arctic, preferring a temperate and warm climate. In cold waters, it does not occur, nor does it live in salted or freshened seas. For example, in the Black Sea, carcarhodone does not appear. The most likely encounter with large white sharks on the coast of California, near the Mexican island of Guadalupe, in the Mediterranean and Adriatic seas, off the coast of New Zealand, where they can swim in small flocks. The waters of the seas, where there are plenty of sea lions or seals, are especially loved by these predators. For a long time there was an opinion about the permanent coastal existence of white sharks, but it is proved that the fish migrates from the coast of California to the African latitudes, sailing over 20 thousand km per year.
Being the largest modern predator (individual specimens reach a length of more than 10 meters with a body weight of up to 3.5 tons), a white shark does not give the victim any chance of escape. Its name is due to the color of the abdominal part - light or dirty white. The dorsal part of it is darker in color: gray, greenish. Like all kinds of sharks, white has no air bubble, which explains the constant movement of the fish.
She is more partial to food than her tiger sister. A small shark feeds on medium-sized fish, mammals. Adult karharodons prey on seals, dolphins, large fish and smaller species. Adults do not bypass young or sick whales, often performing uncommon tactical moves during the attack, which only confirms their intellectual abilities. This dangerous shark has long proved that she has every prey in her teeth.
Little information is available on the reproduction of the offspring. Like many species, it is ovovivorous with a gestation period of 11 months, at the end of which there appear 1-2 cubs adapted to an independent life. Today, the population of white sharks is rapidly decreasing, there are no more than 3,500 pieces worldwide. The species is listed in the Red Book.
Sharks in the ocean - the spectacle is fascinating and frightening at the same time. It can excite and shock. Who saw not only the photos of big sharks, but also a flock of white hunters with their own eyes, will never forget this. Even pictures with images of predatory fish excite the imagination. The world of sharks is amazing, fantastic and dangerous. The most ancient creature and modern cruel predator get along in a unique animal, attracting attention, again and again generating the question: "Is the shark a fish or a mammal?"