Why are some fish endangered?

Many species of fish are endangered and fresh water fish are the most at risk.  There are a number of threats to fish and at the top of the list is overfishing.  Commercial fishing operations often fish out an area faster than the fish can replace those that have been taken.  This is taking its toll on the fish population.  Loss of habitat is another major threat to fish populations around the world, along with pollution.  The introduction of exotic species into an environment has taken out resident fish populations many times.  Finally, the capture of fish for the pet trade so that fish can be put into tanks has had an impact as well.