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.
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Bony fishes (Osteichthyes) are a group of aquatic vertebrates characterized by having a bony skeleton (in contrast to the cartilaginous fishes, a group whose skeleton consists of cartilage, not bone). Bony fishes include two sub groups, the ray-finned fishes and the lobe-finned fishes.
The key characteristics of bony fish include:
- bony skeletons
- swim bladder
- color vision
- lack placoid scales
- posess ganoid, cycloid or cetnoid scales
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