High Quality Content by WIKIPEDIA articles! Fish are very diverse and are categorized in many ways. This article is an overview of some of the more common types of fish. Although most fish species have probably been discovered and described, about 250 new ones are still discovered every year. According to FishBase, 32,100 species of fish had been described by September 2011. That is more than the combined total of all other vertebrates: mammals, amphibians, reptiles and birds.