Fish, along with reptiles, amphibians, mammals and birds, are vertebrate animals. This means they have a skeleton made of bone or cartilidge and a backbone which is also called the vertebral column.
Fish are different from other vertebrate animals because they have gills. Gills allow fish to breathe underwater. Fish dominate the waters of our planet. There are over 25,000 species of fish in the world which means there as many species of fish as there are of mammals, birds, reptiles and amphibians put together. Fish are cold-blooded and have a body temperature which more or less closely follows that of the water in which they live.
England is abundant with water. It has a huge and varied coastline and inland waterways of streams, rivers, lakes, fens, marshes, ponds, canals and reservoirs. Different types of water encourage different types of fish, like the Spiny Seahorse, the Basking Shark, the Three-spined Stickleback and the Weever Fish and all of them are very different to each other. However, they are all fish and they all have gills. The study of fish is called ‘ichthyology’.