While there is no way to know how many fish are in the sea, the number of fish species in the world's oceans, seas and other bodies of water is estimated to be between 27,300 and 32,000 total as of 2014. This number includes both freshwater and saltwater fish.
There are more species of fish than all groups of vertebrates combined. An animal is classified as a fish if it possesses a cranium, fin-shaped limbs, and gills in both juvenile and adult forms. The bony fish, or Osteichthyes, are the largest taxonomic class of vertebrates in existence, containing more than 28,000 known species as of 2014.