Fishes are a different and diverse set of living creatures. No wonder it is so hard to group them as one. However, every fish will have a head for protecting the brain, along with the mouth, eyes, and teeth.
The fins are the limbs that help them move in water, and they are present in pairs. Also, instead of lungs, the gills help them with the breathing. Except for hagfish, most fishes have a vertebra protecting their spinal cord.