Sharks are one of the most formidable inhabitants of the ocean. The lack of bone tissue and Gill covers, especially the structure of scales, and many other features of the structure speak of their ancient origin, as confirmed by paleontological data the age of the first fossil remains of sharks is determined approximately 350 million years. Despite the primitiveness of the organization, shark — one of the most perfect predatory fish of the ocean.
Over a long period of existence they managed to adapt perfectly to life in the water column and now successfully compete with bony fish and marine mammals. Unlike bony fish sharks and rays don’t spawn and lay their large, covered with a Horny shell eggs or give birth to live young.
The highest values reach whale (up to 20 meters) and the so-called giant shark (up to 15 meters). Both these and others, like baleen whales, they feed on planktonic organisms. Wide and gaping jaws, these sharks move slowly in the midst of clusters of plankton and filter the water through Gill openings covered by a network of special outgrowths of surrounding tissue. Giant shark profiltruyte an hour to one and a half thousand cubic meters of water and remove all organisms larger than 1-2 millimeters.
On the reproduction of plankton sharks very little information. Eggs and embryos of giant sharks are generally unknown. The smallest specimens of this species are 1.5 meters in length. The whale shark lays eggs. It’s safe to say that these are the largest eggs in the world, the length of almost 70 inches, width — 40. Planktivorous sharks are slow-moving and quite aggressive.
Some kinds of sharks live near the bottom and feed on benthic mollusks and crustaceans. These are small (not more than a meter in length) leopard sharks. They live near the coast, often forming large shoals. The barbed catches sharks in the Atlantic ocean, sometimes reaches 20 thousand pieces one noticeable takenaga of the Seine.
In the open ocean are found the shark other species, and they do not form shoals, and roam singly or in small groups. Sometimes, these sharks come to the coast, and most attacks on swimmers people do they. Among these predators are the most dangerous white, blue-gray, brindle, blue, long-armed shark and hammerhead shark.
The largest representative of this group of fishes — the whale shark, is not threatening people’s lives; it feeds on small fish and crustaceans. Although statistics show that deaths from sharks is much less than is commonly believed, still to be feared of all sharks, the length of which exceed 1 — 1.2 metres, especially when the water is the blood or the food. Sharks have a phenomenal ability to detect at a great distance an injured or helpless animal in his convulsive movements or fall into the water blood.
Physiologists are still not installed, which senses the shark is guided in search of food. It is believed that she discovers the victim with a highly developed sense of smell, and lateral line system that senses the slightest vibration of low frequency. A significant role, apparently, also play a special hearing and taste organs. One way or another, but as soon as the water reddened with blood, there are sharks, which was nowhere to be seen. An ominous shadow quickly slips into the clear water, headed and accompanied by an escort of fish-pilots.
Shark hunting alone, slowly and quietly. It usually does not attack immediately and its victim often exhibits some caution. When fishing for sharks on special gear from the boat you can see how the long predator circling around the bait until they finally decide to grab it. She attacked swiftly and suddenly. Especially dangerous sharks become when in the water a lot of blood and food. Crazy how they pop up vertically from depth to the surface, popping up from the water and violently grab everything that comes their way, including their relatives. At such moments, they weren’t able to scare away or ward off. Only when the food runs out, vanish and sharks.
Various species of sharks are different lifestyle and are quite different from each other in body structure and behavior. Together with stingrays sharks belong to the most primitive group of fish called cartilaginous because their skeleton consists of cartilage and is completely devoid of bone. If you “pet” a shark or manta ray in the direction from head to tail, their skin seems slightly rough, but the hand movement in the opposite direction will be felt sharp teeth on a coarse-grained emery paper. This is because each lamella cartilaginous fishes supplied by a small spine, tip facing back. Slim on the outside covered with a layer of tough enamel, and the base in the form of widening plates embedded in the skin of the fish. Inside each of the scales consists of blood vessels and nerve. At the edges of the mouth is larger scales, and the mouth of the shark, the spines of the scales reach a considerable value, and serve not as cover but as the teeth.
Thus, the teeth of sharks is nothing like modified scales. It is easy to see that the structure of the scales (and teeth) of sharks in its main features corresponds to the structure of the teeth of mammals. Maybe this discovery not everyone will like, but the fact remains: we inherit our teeth from very remote ancestors, family structure and lifestyle to modern sharks.
The teeth of sharks, and how their scales are arranged in a staggered manner and sit in rows. As it wears out one set of teeth to replace them, a new older, located in the back of the mouth. The shark does not chew food, but only holds tears and tearing her apart, swallowing chunks of a size that can go through its wide throat.
The cartilaginous fish do not have Gill covers, so each side of the body of the shark behind the head can be seen 5 — 7 Gill slits. This external sign of sharks can be easily and accurately distinguished from other fish. Gill slits of manta ray are located on the ventral side and are hidden from the observer’s eye.
It should be noted that these animals, despite experience to the disgust of the people, are of great commercial importance. Used their meat, skin and fat of the liver, containing ten times more vitamin A than cod liver oil. Salted, smoked and specially prepared fresh meat of many shark species is characterized by high taste qualities. One of these fishes, fins which are used to prepare soup (pride, Chinese food), was named the soupfin shark.