Sharks are predatory fish, dangerous and aggressive inhabitants of the ocean, the oldest known animals. So it is believed, and millions of people believe in this, drawing knowledge about these unique creatures from Hollywood horror thrillers. We will figure out what we know about these amazing creatures, which appeared much earlier than all civilizations in the world and perfectly adapted in modern life. What is a shark? Is it a fish or a mammal?
Amazing fish
All scientific and encyclopedic publications claim that sharks are cartilaginous fish, i.e., they have absolutely no bone tissue in their bodies, which makes them strikingly different from their modern counterparts in terms of habitat. Together with the absence of gill covers and structural features of the scales, the cartilaginous ostyak indicates the primitive organization of the species, or rather its ancient origin: it is known that 400 million years ago these fish swam in the oceans. Despite this, sharks are one of the most advanced species of predatory ocean fish. Adapting to a constantly changing environment for a long time, they perfectly adapted and now get on well with modern bony fishes and marine mammals, not inferior to them in speed, dexterity, or hunting skills. The list of sharks includes more than 400 species, polarly different: from the smallest deep-sea, barely growing to 17-20 cm, to the giant - a whale shark, a huge 20-meter multi-ton individual.
An important difference from bony fish are reproduction methods. Some species of sharks are viviparous, i.e., give birth to live cubs. Some lay eggs protected by a dense cornea. Not all the secrets of their life are open: there are species whose secrets of the reproduction of posterity are still sealed with seven seals. Therefore, the question so often arises: "Is a shark a fish or a mammal?"
View Features
The cartilaginous skeleton and the absence of bones are the main signs of the relationship 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 the glory of the most dangerous and aggressive predator. In addition, nature has taken care of protecting this amazing animal. It is difficult to find something that is more protective than the scales that the shark possesses. Located from head to tail, it resembles a satin finish to the touch, but you should not run your hand in the opposite direction - from tail to head: sharp teeth bite into the skin. Coarse sandpaper compared to this perfect protection is a faint resemblance.
Consider the device scales. Each flake of cartilaginous fish is equipped with a small spike with a pointed backward tip. On top of the spike 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 are blood vessels and nerve branches. The size of the scales on the body of the fish is different: the largest is located on the head, the spikes in the shark's mouth, having somewhat transformed, ceased to be protection of the skin and turned into a sharp and extremely dangerous weapon of attack - magnificent teeth.
Main weapon
Being a modified scale, the shark's teeth are arranged in a staggered order, in several rows. Throughout the life of a predator, teeth grow constantly, and when one row is abraded, new ones grow, located in the depth of the mouth. 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 to pieces, to swallow without interference. Different types of sharks have different tooth shapes, which is dictated by lifestyle features. Benthic, feeding on crustacean organisms in hard shells have teeth that are flat with a ribbed surface and can crush the calcareous protection. Predatory fish have long sharp teeth to grab moving prey, or wide with a serrated edge, designed to tear the meat of a large victim. Plankton sharks have practically no need for teeth; these species are small, barely reaching 3-5 mm.
Another feature of cartilaginous fish is the absence of gill covers. Their role is played by 5-7 gill slits located behind the head, the number of which is determined by the type of shark, and the presence is a distinctive feature. However, like all fish, these predators, receiving oxygen from the 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: sense of smell, electro-receptor apparatus and side-line system
It is impossible to overestimate the possibility of smelling in sharks. This is one of the most advanced basic sensor systems. The experiments showed not just a high sensitivity of fish to smells, but truly amazing. The shark can pick up the smell of blood diluted in water in a ratio of 1: 1,000,000, and constantly uses its sense of smell when searching for prey or partners for breeding during the breeding season. In addition to the highly developed sense of smell, other organs and systems are also involved in determining the location of the object: hearing, taste buds, and also a side line located on the surface of the fish’s body, capable of sensing both insignificantly weak mechanical movements and the slightest low-frequency vibrations in water , and which plays an important role in hunting, communicating with brothers and orienteering.
There are still unproven scientific assumptions about the ability of these predators to catch odors spreading through the air, which was prompted by the strange behavior of a 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 heart muscles and the electric fields with insignificant voltage has been scientifically proven. Long-term observation of the migration of some species over fairly large distances in a straight line revealed the possibility of their orientation along the Earth's magnetic field.
Vision
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. The features of the device of the shark's organ of vision are the presence of a blinking eyelid that closes 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 a 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, evidence does not require evidence that the vision of some species of these fish is many times greater than human.
Shark breeding
Unlike most bony fish that produce millions of eggs, reproduction of their own kind in sharks is aimed more at quality than quantity. The characteristic features of cartilaginous fish - internal fertilization, widespread egg production and live births significantly reduce the mortality of offspring, allowing for a high survival rate and lower fecundity.
Depending on the species, sharks can be oviparous, viviparous and ovoviviparous. Oviparous is almost a third of all species. After internal fertilization, the female lays eggs, covered with a proteinaceous gelatinous layer, protected on top of it by a hard shell that 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 is laid simultaneously: 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 little shark is perfectly adapted to life and differs from the adult in size.
A distinctive feature of egg production is that, hatching from fertilized eggs, the cubs remain in the mother's oviduct for some time, being born developed and perfectly adapted to independent existence. Information on the timing of gestation in ovoviviparous species requires clarification. According to some reports, this period is from several months to two years, like a prickly shark, which is a record among all vertebrates.
In the womb of viviparous individuals, up to 30-80 embryos can simultaneously develop. Regardless of the type of shark and the method of reproduction, everyone is distinguished by the reproduction of a small, but capable of independent life offspring.
Plankton sharks
Most of these fish are common in the oceans and seas, living in the water column from the surface to two kilometer depths, and are classified as real predators. But there are exceptions in this family: large-mouthed, giant, whale and some other species of sharks are filtering, feeding on plankton, small fish and squid.
The largest are whale and giant sharks, reaching a length of 20 and 15 meters, respectively. Being planktonic fish, they move slowly, opening their mouth, in the center of plankton accumulations, driving water through gill holes with special outgrowths, filtering out a huge amount of water and extracting from it all living organisms larger than 2 mm.
It is about the reproduction of plankton species that there is very little information. So, the life of a giant shark is completely unknown until now. Whale - ovipositing. The eggs laid by her reach a very impressive size: length can be 0.7 m, width - 0.4 m. Despite the huge 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 lead a benthic lifestyle and feed on crustaceans and invertebrates, such as small cats, no larger than 1 meter in length. The object of fishing is the prickly shark-katran, a photo of which is also presented in the article.
Fishing katran
Katran, having wide distribution, is the only species that lives in the Black Sea. This sea shark is extremely cold-loving and does not favor warm waters. Perhaps this explains the fact that the Black Sea katran rarely reaches 1 meter in length, although in the North Sea the size of this fish is 1.5-2 m. 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 schools. Katrans feed on bottom invertebrates and benthic fish - flounder, merlang, successfully hunt shoals of hamsa.
It is amazing that katran is an ovoviviparous fish, the pregnancy of which lasts incredibly long - up to 2 years. Sharks will be born absolutely ready for the adult life of a predator. Inaccessible to humans, protected and cautious, they grow to adulthood without any problems. These sharks at sea are safe for humans. They never swim close to swimmers. An incredible system of highly developed sense of smell and the sensation of the slightest frequency fluctuations helps the quatran to avoid meeting people.
The schools of this fish approach the shores in late autumn. Then the fishing season begins. The second name of the sharks - prickly - was given to the katrans for a reason. This fish can cause a lot of trouble when it is taken out of the trawl. It possesses not only strong scales, but also sharp spikes in front of the dorsal fins, at the base of which are poisonous glands. In contact with them, you can get a portion of the poison, although not fatal, but bringing certain inconvenience. The Atlantic Ocean is the most generous of catran catches: sometimes it is possible to catch up to 20 thousand fish for one note.
The prickly shark is not just a tasty fish, it is very tender and, of course, useful. In the skillful hands of a good cook, katran meat turns into magnificent delicacies, healthy and delicious dishes. An indispensable rule in the preparation of shark meat is the obligatory discharge of blood immediately after the fish has been caught. It has a high concentration of ammonia. If you do not get rid of blood, the product will be hopelessly spoiled. The advantage of such dishes is the fact that their meat does not have bones, because this fish is cartilage.
The skin of katrans is also appreciated. The abrasive properties of katrana skins have always been used by masters of many industries: from carpenters, cabinet makers and joiners to furriers.
Tiger shark
Fully justifying the reputation of the thunderstorm of tropical seas, the tiger shark, yielding to the 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 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 fade with time. Preferring shallow water, these sharks rarely drop below 300 meters, 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 among the largest species. The streamlined body shape with a large head, a blunt snout and 5 gill slits, as well as a large mouth with jaws equipped with 280-300 flat, scraper-like teeth with serrations, and a well-developed upper tail fin blade are an incomplete portrait of this dangerous fish.
Sea tigers are tied to their favorite places, they do not like to leave the boundaries of their own residence. Being lonely predators, tiger sharks sometimes group in groups if there is enough food. But most often they patrol their area one by one.
The diet of these predators is made up of pinnipeds, 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 far from organic food, surprise researchers. For their exorbitant omnivorous nature, tiger sharks have received the stigma of "marine scavengers." But more than relevant for them is the ability to turn the stomach through the mouth to rinse in water, which allows you to get rid of very indigestible objects, such as cans, bags, various garbage.
This dangerous shark refers to ovoviviparous, bearing their offspring for 14-16 months and giving birth in a litter of up to 80 sharks, each half a meter in size.
Great White Shark
An exceptionally large aggressive predator - the white shark or karkharodon, which has long and firmly held a sad primacy in 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. In cold waters, it does not occur, and also does not live in low-saline or desalinated seas. For example, carcharodon does not appear in the Black Sea. The most likely encounters with great 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 waters of the seas, where sea lions or seals abound, are especially loved by these predators. For a long time there was an opinion about the constant coastal existence of white sharks, but it was proved that fish migrate from the shores of California to African latitudes, swimming 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), the white shark gives the victim no chance of salvation. This species owes its name to the color of the abdominal part - light or off-white. Its back part is of darker tones: gray, greenish. Like all types of sharks, the white one does not have an air bubble, which explains the constant movement of the fish.
She is more biased towards food than her tiger sister. The little shark eats medium-sized fish, mammals. Matured carcharodons prey on seals, dolphins, large fish and smaller representatives of the species. Adult individuals do not bypass young or sick whales, often performing extraordinary tactical moves during an attack, which only confirms their intellectual abilities. This dangerous shark has long proved that it can handle any prey.
Little information is available on the reproduction of offspring. Like many species, it is ovoviviparous with a gestation period of 11 months, at the end of which 1-2 cubs adapted to independent life appear. Today, the population of white sharks is rapidly declining, all over the world there are no more than 3,500 pieces. The species is listed in the Red Book.
Sharks in the ocean - a sight bewitching and frightening at the same time. It is able to delight and plunge into shock. Whoever saw not only photos of large sharks, but also a flock of white hunters with their own eyes, will never forget this. Indeed, even paintings with images of predatory fish excite the imagination. The world of sharks is amazing, fantastic and dangerous. The oldest creature and modern cruel predator coexist in a unique animal, attracting attention, and again and again raising the question: "Is a shark a fish or a mammal?"