A poikilothermic (‘cold-blooded’), legless, aquatic vertebrate that possesses a series of gills on either side of the pharynx, no internal nostrils, and at least one mid-body fin as well as a tail fin. Fish do not form a single taxonomic group (they are paraphyletic) and the old term Pisces is no longer used, but lampreys and hagfish (Agnatha), sharks and rays (Chondrichthyes) in which the skeleton is made from cartilage, and bony fish (Osteichthyes) are described as fish.