[one] Most Fish belong to The category Actinopterygii, which accounts for approximately 50 percent of all living vertebrates. This makes fish simply essentially the most numerous group of vertebrates by variety of species. "Fish" is just not a formal taxonomic grouping in systematic biology. Amphibians, reptiles, birds and mammals all https://maps.app.goo.gl/9y4LfCmrsyYSbzTo6