Gasterosteus is a genus of Perciform fish that belongs to the family Gasterosteidae (sticklebacks). These fishes can be found in the Holarctic region with a circumpolar distribution being found to inhabit freshwater, brackish water and marine habitats.

The oldest known members of this genus belongs to G. aculeatus being found in the Monterey Formation of California, USA probably from the Alta Mira Shale of the Palos Verdes Peninsula. These fossils essentially resemble modern G. aculeatus. It’s fossils are dated to be around 13.0 to 13.3 million years old placing it within the Serravallian age of the Middle-Late Miocene epoch.

There are currently five recognized species in this genus that are extant and another five that are extinct. According to fish species lists by William N. Eschmeyer, an American ichthyologist and founder of the Catalog of Fishes, there were only two species with three subspecies in the genus; G. wheatlandi and G. aculeatus with its three subspecies G. aculeatus aculeatus, G. aculeatus microcephalus and G. aculeatus williamsoni. The species complex of G. aculeatus is well-known and has been extensively studied for this complex exhibiting a wide array of morphological, physiological, ethological, reproductive and genetic variations.

The list of species are found below: