The classification of the 28,000 living fish species varies from one to the next; however, all are part of the Animal Kingdom, the phylum Chordata and the sub-phylum Vertebrata.
Within this sub-phylum, four different classes contain fish, including the Myxini, Cephalspidmomorphi, the Chondrichthyes and the Osteichthyes. These four classes are divided further into numerous families, genera, species and subspecies.