The following outline is provided as an overview of and topical guide to fish:
Fish – any member of a paraphyletic group of organisms that consist of all gill-bearing aquatic craniate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups. Most fish are ectothermic ("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers like white shark and tuna can hold a higher core temperature. Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams (e.g., char and gudgeon) to the abyssal and even hadal depths of the deepest oceans (e.g., cusk-eel and snailfish). At 32,000 species, fish exhibit greater species diversity than any other group of vertebrates.
What type of things are fish?
Fish can be described as all of the following:
Types of fish
History of fish
Fish as a resource
People influential in relation to fish