Fish
| Fish Temporal range: Middle Cambrian – Recent | |
|---|---|
| A cichlid fish, Sciaenochromis fryeri | |
| Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Olfactores |
| Subphylum: | Vertebrata |
| Groups included | |
| Cladistically included but traditionally excluded taxa | |
A fish (pl.: fish or fishes) is an aquatic, gill-bearing animal with a hard skull that lacks limbs with digits. This includes hagfish, lampreys, and both cartilaginous and bony fishes. Some 96% of living fish species are teleosts, bony fishes able to protrude their jaws. The bony fishes or Osteichthyes include the tetrapods, which evolved from lobe-finned fishes; major features such as having jaws and an adaptive immune system evolved in the Osteichthyes.
The earliest fishes appeared during the Cambrian period. Fish continued to evolve through the Paleozoic era, diversifying into a wide variety of forms. Some such as the Placodermi had heavy bony plates that protected them from predators. The first fish with jaws appeared in the Silurian; they greatly diversified during the Devonian, dubbed the "age of fishes".
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 can acoustically communicate with each other, such as during courtship.
Fish are an important resource for humans worldwide, especially as food. Commercial and subsistence fishers hunt fish in wild fisheries or farm them in ponds or in cages in the ocean. They are also caught in recreational fishing, raised by fishkeepers, and exhibited in public aquariums. Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies.