What fish can run, run and swim

What are fish

Fish are divided into two large groups: the cartilaginous and the bony fish.

The skeleton of the cartilaginous fish does not consist of bones, but - as the name suggests - of cartilage. In contrast to the bones, the cartilages are elastic. Cartilaginous fish include sharks, rays and sea dragons.

All other fish belong to the bony fish.

Fish from A-Z

As the name suggests, the skeleton of the bony fish consists of bones - just like other vertebrates. Most bony fish have a swim bladder. It emerged from a bulge in the intestine and is filled with air. It ensures that the fish can float in the water. Fish that do not have a swim bladder - for example the cartilaginous fish - must always keep moving so that they do not sink to the bottom.

Fish lay eggs for reproduction. The young, freshly hatched fish usually have to get by themselves. With some fish species, however, the parents take care of their offspring: They build a nest out of aquatic plants or stones, lay their eggs in them and guard them until the young fish hatch. In still other species - such as the dogfish or the hammer shark - the eggs develop in the mother's womb and the young are born alive.

In search of a habitat, fish have settled in different bodies of water over the course of millennia and have adapted accordingly to their surroundings. Two thirds of all fish species live in the sea, i.e. in salt water. The rest live in the fresh water of lakes and rivers.

The smallest fish is the goby; it measures just eleven millimeters. The largest are the whale shark, which is up to 14 meters long, and the giant manta, which is up to seven meters wide.