Rhinogobius brunneus, the common freshwater or the Amur goby, is a complex of several species in the family Oxudercidae.

The first dorsal fin is tall and triangular shaped while the second is shorter, rounded, and begins at the midbody.

For instance, this contrasts with a similar species, R. mizunoi, which has 13-18 predorsal scales and does not have vertical dark lines or spots on the caudal fin.

R. brunneus fry will drift downstream to the ocean and ascend back up streams as three-month-old juveniles.

Males build nests under rocks in the freshwater rapids and runs but return to the pools to look for females.

Male gobies of some species in this complex will perform courtship displays to attract females.

Females prefer males that court in faster currents, as it is an honest sign of good physical ability.

Female choice of males was not affected by sexually dimorphic traits such as body size[11].

[7] Rhinogobius brunneus abundance has decreased significantly and is classified as an endangered species in the Fukui Prefecture of Japan.

The species live in short rivers, which are threatened by riverbank management work, dams, etc.