Some wild populations have evolved a complex amphidromous breeding strategy in which adults live and spawn in freshwater or brackish streams and the pelagic post-hatch larvae are washed downstream to the sea where the post-larval fry spend the first part of their life developing in estuarine nursery zones under brackish to full marine conditions.

Once they reach a certain stage of development they begin to migrate upstream with some mov…

There are a number of unidentified species within the grouping of which several are referred to using a two-letter code based on their respective colour pattern for ease of reference, with ‘CB’ shorthand for ‘cross band’, for example.

R. sp. ‘CB’ is the commonest member of the grouping in Japan but has not yet entered the international aquarium trade as far as we know.

As is typical for the genus eggs are deposited on the ceiling of a cave or crevice and guarded by the male until hatching.

Several potential sites should be offered in the form of rocks (flat slate tends to be easiest to handle, see below), terracotta pipes, plant pots, etc.

A nuptial male will select a site and defend it agai…

Known from various parts of the middle and upper Mekong river basins with record existing from the Nam Tha, Nam Ou, Nam Khan, Nam Lik, Nam Ngum and Nam Mang tributary systems in Laos, the Nam Noeua (a tributary of Nam Ou) in Vietnam, and the Mae Nam Kok in Thailand.

Occurrences in the Chao Phraya drainage in central Thailand most likely refer to the congener R. chiengmaiensis.

This species has been exported for the ornamental trade but often labelled as the congener R. mekongianus.

Although the two do appear relatively similar R. chiengmaiensis can be identified by a combination of external characters including: presence of 5 irregular dark markings on the body (vs. 7-8 i…

This species’ name has appeared quite regularly on ornamental fish trade lists since the mid-00’s but it’s unclear whether the species itself has ever been exported since fish labelled as such do not appear to fully match the most recent key (see below).

That said, its natural habitats lie in the same region as the loach Yaoshania pachychilus so it’s reasonable to assume that some specimens may have been collected, and the fish in our images were ca…

This species was previously considered to be a subspecies of R. nagoyae but has generally been accepted as distinct since 2008.

It can be told apart from other Rhinogobius spp. from Taiwan by presence of irregular, wavy, reddish brown lines on the cheek and opercle.

This species may not yet have appeared in the ornamental trade but it has been collected by a few individuals.

It can be told apart from related species from Taiwan by possessing 30-32 longitudinal (lateral) scales vs. 32-39 in other species, and 6-8 scale rows between the origin of the first dorsal-fin and upper pectoral-fin base vs. 9-15 in other species.

It’s unlikely that this species has been in the aquarium hobby given its natural range and the lack of commercial fishing for the ornamental trade in that area.

Among congeners it’s most similar to R. davidi but can be told apart by presence of 8 (vs. always 9 in R. davidi) soft dorsal-fin rays, 10 (vs. 11-12) transverse scale rows, and 6-7 (vs. 8-10) scales between the first dorsal-fin origin and upper pectoral-fin base.

This species appears to exist in a number of different forms which exhibit differences in colour pattern, morphology, or both, and it’s currently unclear whether all of them are truly conspecific or not although those in the aquarium trade all appear similar to one another.

We’ve been unable to obtain a copy of the original description so it’s not currently possible to provide a detailed diagnosis either, with most recent studi…