How are fish classified?

Answer 1

Fish are classified in the kingdom Animalia, and within that they are nested into the phylum Chordata, subphylum vertebrata. Beyond that, extant(modern day) fish are grouped into several classes; Agnatha (jawless fish-hagfish, lamprey, ~100 species), Chondrichthyes(cartilagenous fish - sharks, rays, skates, chimeras, ~950 species), and the vast majority of modern fish (30 000 species) are in the class Osteichthyes(bony fish), of which most in that group are in the subclass Actinopterygii, the ray finned fishes. The only other extant group is a small sister group of the Actinopterygii, the Sarcopterygii, which consists of only the ancient Coelacanth, Latimeria chalumnae, and a few (6) species of Lung Fish.
There are a great number of ways to classify fish. Fish can be classified by environment, size, coloring, and diet.

Answer 2

Fish are classified as aquatic vertebrates that breathe through gills and have fins for swimming. They are further classified into three main groups: jawless fish (like lampreys), cartilaginous fish (like sharks and rays), and bony fish (like salmon and tuna). These groups are then divided into various classes, orders, families, and species based on their characteristics and evolutionary relationships.