FISH Fish Fossil range: Ordovician–Recent PreЄ Є O S D C P T J K Pg N A giant grouper at the Georgia Aquarium , seen swimming among schools of other fish The ornate red lionfish as seen from a head-on view Scientific classification Kingdom: Animalia Phylum: Chordata (unranked) Craniata Included groups Jawless fish † Armoured fish Cartilaginous fish Ray-finned fish Lobe-finned fishes Excluded groups Tetrapods Fish are a paraphyletic group of organisms that consist of all gill -bearing aquatic vertebrate (or craniate ) animals t...