thumb Atlantic herring, Clupea harengus,one of the most abundant species in the world - Photo
A fish is a poikilothermic (cold-blooded) * water-dwelling vertebrate with gills. There are over 27,000 species of fish, making them the most diverse group of vertebrates. Taxonomically, fish are a paraphyletic group whose exact relationships are much debated; a common division is into the jawless fish es (class Agnatha, 75 species including lampreys and hagfish), the cartilaginous fishes (class Chondrichthyes, 800 species including sharks and rays), with the remainder classed as bony fishes (class Osteichthyes).
Fishes come in different sizes, from the 14-meter (45 ft) whale sharkThe whale shark Rhincodon typus is a large, distinctively marked member of the subclass Elasmobranchii of the class Chondrichthyes. It is the largest shark and also the largest fish. The greatest size accurately recorded was 14 m long, but lengths up to 2 to a 7-mm (just over 1/4 of an inch) long stout infantfish. Many types of aquatic animals named "fish", such as jellyfishThis article is about jellyfish, the sea creatures. For the pop band, see Jellyfish (band). Stauromedusae Coronatae Semaeostomae Disc jellyfish Rhizostomae Jellyfishes (also called jellies or sea jellies as they are not true fish) are animals that belong and cuttlefishSepiadariidae Sepiidae Cuttlefish are animals of the order Sepiida and are marine cephalopods, small relatives of squids and nautilus. Description Cuttlefish have an internal shell, large eyes, and ten arms furnished with denticulated suckers, by means of, are not true fish.
* Certain species of tunaThunnus alalunga Thunnus albacares Thunnus atlanticus Thunnus maccoyii Thunnus obesus Thunnus orientalis Thunnus thynnus Thunnus tonggol Tuna are several species of ocean-dwelling fish in the family Scombridae, mostly in the genus Thunnus . Tuna are fast maintain an elevated core temperatureCore temperature refers to the operating temperature of an organism, specifically in deep structures of the body such as the liver, in comparison to temperatures of peripheral tissues. Temperature is part of a homeostatic mechanism designed to keep the or, so they are not, strictly speaking, poikilothermic. The Great White SharkThe Great White Shark Carcharodon carcharias , also known as White Pointer White Shark or Amaletz is an exceptionally large lamniform shark found in coastal surface waters in all major oceans. Reaching lengths of 7. 2 metres (23 ft 7 in) and weights of 3, is the only known truly endothermicAn endotherm is an animal that can control its body temperature by the regulation of its metabolic rate. Endotherms include birds, mammals, and insects. The advantages of endothermy are increased enzyme activity and a constant body temperature, allowing t (warm-blooded) fish.
1 Note on usage: "fish" vs. "fishes"
"Fishes" is the proper English plural form of "fish" that biologists use when speaking about two or more fish species, as in "There are over 25,000 fishes in the world" (meaning that there are over 25,000 fish species in the world). When speaking of two or more individual fish organisms, then the word "fish" is used, as in "There are several million fish in the species Gadus morhua" (meaning that G. morhua comprises several million individuals). To see both in action, consider the statement "There are twelve fish in this aquarium, representing five fishes" (meaning that the aquarium contains twelve individuals, some of the same species and some of different species, for a total of five species).
