Sharks are a separate class of vertebrates, the so-called cartilaginous fish. They differ in many characteristics from the class of bony fish such as salmon, trout or tuna. Their lines of development separated over 440 million years ago.
Since sharks are hunters and top hunters, they reproduce very slowly. Nevertheless they are hunted like bony fish, which reproduce much faster.
Sharks can be found almost everywhere. They populate the high and deep sea, but most sharks live on the continental shelves. Some species even live in fresh water.
Anatomically there are differences between sharks and bony fish. Sharks have, for example, a light, elastic cartilage skeleton, a large liver for buoyancy and a spiral gut.
Sharks are masters of the senses. They see better in the dark than cats, they can feel the finest differences in pressure, they have an excellent sense of smell and a seventh sense for electric fields.
Some 30 % of sharks lay eggs. But 70 % give birth to live young. Sharks become sexually mature very late and bear few young. This makes them vulnerable to overfishing.
