The fish family includes a wide variety of vertebrate animals that live in the water. Although there are over 31,500 different types of fish, with many diverse characteristics, the one thing that fish have in common is that they breathe oxygen from the water through gills. Fins are also a common characteristic of fish, although not all fish have fins. A fish uses fins to propel itself through the water. Some fish can swim at very fast speeds through the water.
Fish vary in size from the goby fish at less than one inch, to the whale shark at over 50 feet. Most fish are cold blooded, meaning their body temperature is not internally regulated. Their body temperature fluctuates with the changing temperature of the water surrounding them. Unlike humans, who have skin covering their body, most fish have scales covering their body.
Fish are an important source of food for humans. For this reason, humans are becoming quite concerned about polluting the ocean, and the effect that ocean pollution is having on fish.