''Neogobius bathybius'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of goby

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to the

Caspian Sea The Caspian Sea is the world's largest inland body of water, often described as the world's largest lake or a full-fledged sea. An endorheic basin, it lies between Europe and Asia; east of the Caucasus, west of the broad steppe of Central Asia ...

, where it occurs in depths down to . It is strictly confined to the brackish-water basin and does not enter

fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

s. It can grow up to a length of TL. The species was transferred to the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

Ponticola ''Ponticola'' is a genus of gobies native mostly to fresh waters of the Black Sea - Caspian Sea region in Eurasia. Some species occur in the brackish-water Black and Caspian seas themselves. It was considered to be part of the broader goby subfam ...

'' from ''

Neogobius ''Neogobius'' is a genus of goby native to Black Sea and the Caspian Sea basins. It is part of the broader Benthophilinae subfamily which is also endemic to the same region. Nevertheless, two ''Neogobius'' species have recently turned out to be h ...

'' on the basis of relationship revealed in molecular investigations.Neilson M.E., Stepien C.A. (2009) Escape from the Ponto-Caspian: Evolution and biogeography of an endemic goby species flock (

Benthophilinae The Benthophilinae are a subfamily of gobies endemic to the Ponto-Caspian region (including the Marmara, Black, Azov, Caspian, and Aral Seas). The subfamily includes about 50 species. The representatives of the subfamily have fused pelvic fins a ...

: Gobiidae:

Teleostei Teleostei (; Ancient Greek, Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest class (biology), infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of a ...

). Molecular Phylogenetics and Evolution, 52(1): 84-10

/ref> On the other hand, recent molecular studies have proven that this species belongs entirely to the genus ''

''.

References

Neogobius Fish of the Caspian Sea Fish of Western Asia Taxa named by Karl Kessler Fish described in 1877 Endemic fauna of the Caspian Sea {{Gobiidae-stub