Fishes are the most diverse group of animals with backbones. Fishes are found virtually anywhere there is water. They are found from the tropics to the poles, in the deepest ocean trenches to the highest lakes, and in water with varying amounts of salt from freshwater to hypersaline lakes. Many fishes live in total darkness deep in the open ocean and in caves. They range in size from a few centimetres to over 10 metres. They range in shape from that of a ball to flatfish or slim eel. Some spend their lives in a few square metres, while others may traverse oceans during their lives. Although the group has diversity of forms and life styles they all possess the following characteristics:

• An elaborate brain and sensory system.
• To swim by contracting segmented blocks of muscles on each side of your body (myomeres).
• A thickened skeleton around your brain.
• Five to nine gill arches.
• A circulation system with a 3 chambered heart.
• A skeleton made of bone and/or cartilage.