This Fish Ontology is an ontology created as how the author views the fish structure following the book "The Diversity of Fishes: Biology, Evolution and Ecology" as the main reference, which covers one part of view on ichthyology, with an emphasis on diversity and adaptation. This ontology is created with the mindset of categorizing fish automatically based on the attributes and terms mined from the fish specimen. Most of the basic organization from this ontology follows Nelson's research due to its synthetic and broad approach, while recognizing that Nelson's conclusions are one of many alternative interpretations of the literature, which is mostly agreed by our main references, and many fish and fisheries researchers. Most of the classification used in this ontology is in no means completed and just following the recent classification provided by the books For now our work focused more on two group of fish which is early jawless fish, and advanced jawed fishes. The classification from both of this group are structured following the reference.