Genus of fishes
Cottus is a genus of the mainly freshwater ray-finned fishes belonging to the family Cottidae, the typical sculpins. They are often referred to as the "freshwater sculpins", as they are the principal genus of sculpins to be found in fresh water. They are native to the Palearctic and Nearctic.
They are small fish, mostly less than in length, although a few species can reach twice that size.
Taxonomy.
"Cottus" was first proposed as a genus by Carl Linnaeus in the 10th edition of the "Systema Naturae" when he described the European bullhead ("Cottus gobio") and in 1850 this species was designated as the type species of the genus by the French ichthyologist Charles Frédéric Girard. The 5th edition of the "Fishes of the World" classifies this genus within the subfamily Cottinae of the family Cottidae. Other authorities have found that the Cottidae, as delimited in the 5th edition of Fishes of the World, is paraphyletic and that the monophyletic grouping is the freshwater sculpins, including the Baikal sculpins, while most of the marine taxa are classified within the family Psychrolutidae. 
 "Cottus kazika" has been found to be outside of a monophyletic "Cottus" and has been classified in the monospecific genus "Rheopresbe".
Species.
There are currently around 70 recognized species in this genus:
Etymology.
"Cottus" is derived from the Greek "kottos", and is a latinisation that word, the original form of it being "koviós" or "kóthos". This is likely to mean "head" and is the word for a small fish with a large head, and is now used for sculpins.
References.
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