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Fish are aquatic vertebrates that have skin covered with scales, two sets of paired fins, some unpaired fins, and a set of gills. Fish do not represent a single clade but are instead paraphyletic. They include hagfishes, lampreys, lobe-finned fishes, cartilaginous fishes and ray-finned fishes.
Cartilaginous Fish
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Cartilaginous fish are so named because instead of bony skeletons, their body frame consists of cartilage. Tough and flexible, cartilage provides enough structural support to enable these fish to grow to incredible sizes. Cartilaginous fish include sharks, rays, skates and chimaeras.
Ray-Finned Fish
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Ray-finned fish are the most diverse of the three groups of fish. The group includes mor than 23,000 species such as salmon, trout, lanternfish, cavefish, cods, anglerfish, tarpon, herrings, electric eels and many others. In contrast to cartilaginous fish, the skeleton of ray-finned fish is composed of true bone.
