Movement of Fish in Water
Fish are vertebrates. All vertebrates have an internal skeleton made up of bones; a tough, elastic substance called cartilage; or both.
Most fish have a streamlined body – the head and the tail are narrow; the middle portion of the body is broader. This kind of shape offers least resistance to the flow of water and makes it easier for them to swim through water. Aeroplane, ship, and boat also have streamlined shapes to reduce resistance to the flow of air and water.
Fish have fins and a flexible backbone that help them to swim. Most fish have a special structure called swim bladder that can be filled with air or emptied to help them