A shark is a rather frightening image, just think of the many horror movies where these toothy creatures act as the main villains. But everything is far from being so unambiguous! Not all sharks are dangerous to humans, and in general, the variety of their species is amazing.
Fact number one.
Most shark species are characterized by a torpedo-shaped body and oval-conical head. This body shape allows this sea creature to move easily and with great speed in the water column. The fish moves due to the wave-like motion of the body, as well as due to the work of all fins, especially the tail fin. The tail fin also serves as a steering device and consists of two blades — the upper and lower, with the upper part goes to the spine. Thanks to the lateral fins, the shark maneuvers both horizontally and vertically. Thanks to the work of the paired fins, the shark maintains its balance in the water, and thanks to this complex system of movement, the shark is able to perform unique tricks. The only disadvantage is that the shark cannot move backwards, although it does not need to. Some shark species walk along the bottom on their pectoral and pelvic fins as if they were standing on their feet.
Fact number two.
Sharks, due to their physiological structure, are simply condemned to constant movement. Naturally, all living creatures need oxygen, but sharks do not have gill covers that allow water to pass through them. Therefore, a shark has to swim with its mouth ajar to capture water, otherwise oxygen will not reach all of its organs. As the fish passes water through its mouth, it removes it through its gill holes. Some sharks manage to slow down, especially when they move against the current or pass water through their gills by pulling it into their mouths. Some shark species that live near the bottom are thought to be able to breathe through their skin. Studies have found an increased concentration of myoglobin in the muscle tissues of sharks, which allows these fish to overcome the constant stress associated with constant movement. The cerebellum and forebrain are responsible for coordination in the water column and complex movements that are associated with more advanced parts of the brain.
Fact number three.
The anatomy of the shark’s jaw is unique — its upper part is not connected in any way to the bones of the skull itself, and therefore it moves quite freely. At the moment of biting, the lower jaw grips the victim firmly, and the upper jaw powerfully chops it horizontally and vertically.
Fact number four.
To fall asleep, the shark has two options. It can do this while moving, since movements are controlled by the spinal cord, or alternately disconnect the left and right hemispheres of the brain. This, by the way, is what dolphins do as well.
Fact number five.
It is believed that the sharks have rather poor eyesight; they can distinguish only the contours of objects and cannot distinguish colors. There are cases where sharks literally do not notice a stationary live object, but when it begins to move, the sharks immediately react to it. Despite this, the eyes of predators have protective elements in the form of skin folds or membranes. A feature of the inner and middle ear structure is that sharks are able to hear low-frequency vibrations inaccessible to the human ear. Thanks to this feature, the shark picks up the movements of the layers of water. If the predator is completely blinded, it has no trouble finding food. It smells blood even if a drop of it is dissolved in the volume of water of a standard swimming pool. Scientists have discovered that some shark species are able to recognize odors that spread not only in the water but also in the air.
Fact number six.
A shark’s lifespan depends on a constant change of teeth. Over its lifetime, a predator changes a total of up to 50,000 teeth. If a predator loses teeth in its mouth, it will starve to death. A shark’s dental system is a kind of conveyor belt: as soon as one tooth falls out, a new one appears in its place. Each species has its own tooth and jaw structure, which is related to its diet. Plankton-eating species have the smallest teeth, while carnivorous species have large, powerful and sharp teeth that easily enter the flesh of potential prey. Sharks that live on the very bottom are armed with flat and ribbed teeth, which sharks use to crush shells.
Fact number seven.
Sharks have a fairly extensive diet, as does the vast food base of the world’s oceans. The stomach of sharks is designed so that by stretching it, it can not only digest food, but also store it. The main component of gastric juice is hydrochloric acid, which dissolves even metal. Therefore, it is well known that sharks do not limit themselves in eating and are able to swallow everything they meet on their way. Having caught its prey, the shark easily gets rid of it due to its sharp teeth and highly mobile jaws. The lower jaw serves as a kind of support, and with the upper jaw it crushes its prey like an axe. Sometimes sharks use their mouth, a cheek pump.
Fact number eight.
Sharks reproduce using the process of internal fertilization, where the male inserts his sexual products inside the female. This process is quite brutal, as the male holds his partner so tightly that she has to heal her wounds afterwards. There have been cases of parthenogenesis in captive sharks where offspring are born without males. Scientists believe that this is a protective mechanism that ensures the survival of the species in the wild.
Fact number nine.
Shark fins are practically a cure-all for all diseases, including cancer. At present, scientists have not yet been able to prove that this is true. This opinion is due to the fact that many believed that sharks do not get cancer. Currently, they managed to prove that this is not true, since individuals were caught in which malignant neoplasms were noted. And this also applies to those individuals who were kept in artificial conditions. Oddly enough, but shark fins are valued more than shark meat, and dishes cooked from shark fins cost crazy money in restaurants.
Fact number ten.
Sharks live in all oceans and seas. Cartilaginous fish prefer coastal waters, reef areas, equatorial and near-equatorial waters. Some shark species are equally comfortable in both salt and fresh water. Therefore, they can swim in rivers. Rare cases are also known when predatory species of sharks have swum into the waters of the Black Sea. Some sharks may temporarily swim into the southern part of the Crimean coast and the western territories of Krasnodar Krai.