At present, about 400 species of sharks are known: from the smallest (15 cm in length) to giants (18 m in length). They have their own characteristics, but there are common features inherent in almost all types:
- Sharks are not intelligent animals, the ratio of their brain to body weight reaches the performance of some mammals.
- Life expectancy is 30 years.
- Sharks have a strong sense of smell and hearing, and there is also an unusual sensory organ, Lorenzini's electroreceptors.
- They pick up electromagnetic waves.
- The skeleton of sharks is cartilaginous.
However, there are a number of features that distinguish sharks from other animals and add great mystery: for example, how the shark sleeps, how it eats, moves and hunts.
Jaw structure
Huge teeth 5 cm long inspire horror. On average, a predator has 4-6 rows of teeth, but some individuals can have up to 20. When the front tooth falls out, the tooth from the back row moves to replace it. By the way, losing teeth for a shark is a common thing. For 10 years, an individual tiger shark is able to change up to 24 thousand teeth. The change process occurs at such a frequency due to the structural features of the jaw: the teeth are attached directly to the gum.
Lack of a swimming bladder
Unlike other fish, sharks lack a bubble. Therefore, the animal is constantly in motion. If you stop working with the tail, the shark will sink to the bottom. Despite the absence of a bubble in all individuals, there is a species of predator that can be afloat without additional effort. This is a sand shark: it is able to swallow air and keep it in itself for several hours.
How the shark sleeps
Answering the question about how the shark sleeps, you need to understand that she does not have sleep as such. Rather, the process can be called a vacation. Predators living near the shore or in smaller reservoirs provide a place for "sleep" in underwater caves. There, the shark is as if sleeping - it lies at the bottom without movement.
And how do sharks sleep in the oceans? Sharks that live in deep waters almost never sleep, because, having ceased to work with their tails and fins, they will plunge to a greater depth, not intended for them. It’s easier for those individuals who live permanently at depths — they can find time to “sleep”. Speaking about whether sharks sleep, one can safely give a negative answer.
Hunting for prey
Sharks are very bloodthirsty. Feeling the slightest smell of blood, they immediately go in search of a victim. Developed sense of smell helps them in hunting. Only 1 gram of fish blood per 1 million grams of water is enough to feel the victim. However, if you close the nostrils to the predator, then there will be no reaction to the victim, and the shark will swim by.
When the shark has already sensed its prey, it may begin to "hungry rabies." At this moment, the predator shows a special rage, he destroys and swallows everything in the way. In the end, in the stomach, which is able to expand several times, there may be many unusual things.
As for sharks who prefer plankton and small fish, these species pass more than one hundred liters of water through themselves to enjoy their favorite food. They are not dangerous to humans and are peaceful.
Interesting facts about sharks
Sharks are rather unusual creatures that can be talked about endlessly. They exist for millions of years and at the same time perfectly adapt to any living conditions. Predators survived dinosaurs and are clearly not going to die out. Here are some more interesting facts about sharks:
- Shark cubs have teeth at birth.
- Sharks can distinguish colors.
- The main food of the Polar sharks are polar bears and deer.
- Some species can jump to a height of 10 m.
- To saturate the body, an animal needs 3-14% of its own body weight per week.
- There are long-lived sharks, whose life expectancy reaches 100 years.
Having learned how sharks sleep, how they feed and exist, we can understand that this is a unique species of fish that has a long history.