Babka gymnotrachelus
The racer goby (*Babka gymnotrachelus*) is a Ponto-Caspian species adapted almost exclusively to the fluvial environment. It is a discreet benthic fish that prefers the beds of large rivers. Although less known to the general public than the round goby, it plays an important role in the Danube River ecosystem, being a good indicator of substrate quality and a food source for large freshwater predators.
It has an elongated body with a relatively small head and rounded snout. The general colour is greyish-yellow, marked by a series of irregular dark oblique stripes running from the back towards the flanks. A distinctive feature is the nuchal zone (nape) and upper part of the back, which lack scales or have very small scales, unlike the round goby which is fully covered in scales.
It is present in rivers flowing into the Black Sea and Caspian Sea. In Romania it occupies the entire lower course of the Danube, Delta arms and the lower reaches of major tributaries (Siret, Prut). It prefers areas with moderate current and mixed substrate (sand, gravel, shells), generally avoiding areas with very deep mud or extremely dense vegetation.
It is an active benthic fish that feeds by exploring the substrate. Its diet consists of various invertebrates: amphipod crustaceans, aquatic insect larvae and small molluscs. It is capable of preying on the fry of other fish when the opportunity arises. Although a bottom fish, it is a better swimmer than other gobies, capable of rapid movements over short distances.
Reproduction occurs between April and June. The male chooses a sheltered site under stones or inside large mussel shells (*Anodonta*). The female lays the eggs, which are guarded and cared for by the male until hatching. Juveniles remain in shallow, quiet waters near the bank until they reach a size that allows them to venture into the main river current.
The species is classified as Least Concern (LC). Danube populations are stable and appear to be expanding upstream as a result of fluvial habitat changes. The main risk to the species is chemical pollution of sediments and morphological alteration of riverbeds through hydraulic engineering works.
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