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A fish (pl.: fish or fishes) is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits.Fish can be grouped into the more basal jawless fish and the more common jawed fish, the latter including all living cartilaginous and bony fish, as well as the extinct placoderms and acanthodians.
Fish systematics is the formal description and organisation of fish taxa into systems. It is complex and still evolving. Controversies over "arcane, but important, details of classification are still quietly raging".
Ribbonfish possess all the characteristics of fish living at very great depths. Their fins especially, and the membrane connecting them, are of a very delicate and brittle structure. In young ribbonfish, some of the fin-rays are prolonged to an extraordinary degree, and sometimes provided with appendages.
The anatomy of fish is often shaped by the physical characteristics of water, the medium in which fish live. Water is much denser than fish, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does. The body of a fish is divided into a head, trunk and tail, although the divisions between the three are not always ...
The guppy (Poecilia reticulata), also known as millionfish or the rainbow fish, [3] is one of the world's most widely distributed tropical fish and one of the most popular freshwater aquarium fish species. It is a member of the family Poeciliidae and, like almost all American members of the family, is live-bearing. [4]
Yet only one species, the burbot (Lota lota), is a true freshwater fish. [2] Common characteristics include the positioning of the pelvic fins (if present), below or in front of the pectoral fins. Gadiformes are physoclists, which means their swim bladders do not have a pneumatic duct. The fins are spineless.
Osteichthyes (/ ˌ ɒ s t iː ˈ ɪ k θ iː z / ost-ee-IK-theez), [2] also known as osteichthyans or commonly referred to as the bony fish, is a diverse superclass of vertebrate animals that have endoskeletons primarily composed of bone tissue.
Cod (pl.: cod) is the common name for the demersal fish genus Gadus, belonging to the family Gadidae. [1] Cod is also used as part of the common name for a number of other fish species, and one species that belongs to genus Gadus is commonly not called cod (Alaska pollock, Gadus chalcogrammus).