Of Fish

Almost three Forth's surface covered with water. This water is home to more than 20,000 species of fish. The earliest fossils of fish from more than 400 million years.

There are different types of fish - from the goby that less than half centimeters long, with the whale sharks, which can be more than 60 meters.

Most fish breathe through gills. Gill gas exchange between water and fish blood. They allow the fish to breathe oxygen in the water.
Fish

Fish are vertebrate animals that have a skeleton made of bone or cartilage. About 95% of the fish have skeletons made of bone. These bony fish have swim bladders, pockets full of gas that can inflate or air so that they float in the water, not swim though. Fish with cartilaginous skeletons are usually heavier than water and sink. You have to swim to stay afloat. Chondrichthyes (cartilage) of fish, including rays and sharks.