Rhinogobius flumineus

Rhinogobius: from the Greek rhinos, meaning 'nose', and the generic name Gobius.

flumineus: from the Latin flumen, meaning 'river' with the full name meaning 'riverine', probably in reference to the fact that this species is not amphidromous.

Endemic to Japan where it's distributed throughout central and western regions of Honshu, the nation's largest island, plus the smaller islands of Kyushu and Shikoku, with the prefectures of Toyama and Shizuoka appearing to represent it's eastern limit in northern and southern parts of the country, respectively.

Type locality is 'Sôshagawa River at Oshita, Ochigun District, Ehime Prefecture, Shikoku, Japan'.

Inhabits smaller rivers, tributaries and streams with substrates of gravel, rocks, boulders, and exposed bedrock which undergo seasonal variations in water flow rate, depth and turbidity.

It's entire life cycle takes place in freshwater although it does occur sympatrically with amphidromous congeners at some localities.

An aquarium with base dimensions of 75 ∗ 30 cm30 ∗ 12 in should be large enough to house a small group.

Should not prove difficult to maintain under the correct conditions; as per other Rhinogobius spp. we strongly recommend keeping it in a tank designed to simulate a flowing stream with a substrate of variably-sized rocks, sand, fine gravel, and some water-worn boulders.

This can be further furnished with driftwood branches, terracotta pipes, plant pots, etc., arranged to form a network of nooks, crannies, and shaded spots, thus providing broken lines of sight.

While the majority of aquatic plants will fail to thrive in such surroundings hardy types such as Microsorum, Bolbitis, or Anubias spp. can be grown attached to the décor.

Like many fishes that naturally inhabit running water it's intolerant to accumulation of organic pollutants and requires spotless water in order to thrive, thus weekly water changes of 30-50% tank volume should also be considered routine.

Though torrent-like conditions are unnecessary it does best if there is a high proportion of dissolved oxygen and some water movement in the tank meaning power filter(s), additional powerhead(s), or airstone(s) should be employed as necessary.

Rhinogobius spp. tend to be opportunistic carnivores feeding on a range of small invertebrates, crustaceans and similar in nature.

In the aquarium they should be offered small live or frozen foods such as chironomid (bloodworm) or mosquito larvae, Artemia, Daphnia, Mysis, etc.

Dried foods may be accepted following a period of acclimatisation but should not be used regularly.

This species may not yet have appeared in the ornamental trade although its name is sometimes applied to other species.

Following the key in Chen et al. (2008) it can be told apart from similar congeners by the following combination of characters: preopercular canal and posterior oculoscapular canal present; postorbital region with paired pore ω; preopercular canal always with 3 pores; 9-11 scales between origins of first dorsal and pectoral fin; caudal-fin with a large, basal <-shaped brownish black marking occupying around ⅔ of its depth in all females.

In addition, there appear to exist two colour forms based on male dorsal-fin morphology and patterning; one in which the 4th ray of the first dorsal-fin is longest with a square bluish-black blotch on the anterior ⅔ of the fin, and a second in which the 2nd and 3rd rays of the first dorsal-fin are longest with the fin itself paler and lacking dark markings.

Please note that at the present time we do not have any images of the 'blotched dorsal' form with all those attached to this profile depicting the 'pale dorsal' form.

It's included in the R. brunneus group of closely-related species within the genus of which members share the following combination of characters: predorsal naked, or with small cycloid scales, the scaled area never extending beyond the vertical of the posterior margin of the preoperculum; cheek with 2 mainly horizontal rows of sensory papillae.

It belongs to an assemblage of fluvial, land-locked, non-diadromous Rhinogobius spp. which have relatively large eggs and 27-29 vertebrae.

The Gobiidae is the most speciose vertebrate family and notoriously problematic in terms of identifying fishes down to species level.

Within this sizeable assemblage Rhinogobius is often included in the subfamily Gobionellinae alongside genera such as Brachygobius, Chlamydogobius, Mugilogobius, Pseudogobiopsis, Schismatogobius, and Stigmatogobius.

Members can be told apart from these and all other gobiid genera by the following combination of characters: head with four simple, longitudinal infraorbital sensory papilla rows a, b, c, and d, single cp papilla, and paired papillae in mental row f; head canal variable from complete loss to normal development of anterior and posterior oculoscapular canals, and preopercular canals, and always with double interorbital pores λ if the pore is present; body mostly covered with ctenoid scales; longitudinal scale series 25–42; head including cheek, snout, opercle, anterior part of nape as well as pre-pectoral region all naked; D1 usually VI; D2 I, 6–11; A I, 5–11; P 14–23; and V I, 5 + I, 5, forming a rounded disc with frenum present, performing two pointed spinous lobes, the spinous ray usually longer than the first branched ray; dorsal pterygiophore formulae modally 3–22 1 101; vertebrae 25–29, usually 26 for most landlocked species.

The genus is widely-distributed throughout much of continental Asia in Russia, Korea, China, Vietnam, Laos, Cambodia, and Thailand, plus numerous islands of the Western Pacific including Japan, Taiwan, Hainan, and the Philippines.

There currently exist over 60 recognised species with many more awaiting formal description, and a number of the described ones are only considered nominal taxa pending additional study.

Those exhibiting similarities in appearance, morphology and behaviour are therefore often aggregated in nominal species groups, e.g., the R. brunneus group, R. duospilus group, etc., for ease of reference.

The fused pelvic fins form a structure normally referred to as the 'pelvic disc', a common feature among gobiids which is used to adhere to rocks and other submerged surfaces.

Rhinogobius spp. also exhibit different reproductive strategies depending on environment, with those inhabiting rivers connected directly to the sea typically amphidromous, and those landlocked in upper reaches of rivers or lakes non-diadromous.

Many of those appearing in the aquarium trade have proven difficult to identify for a number of reasons including:

- taxonomic confusion.
- lack of aquarium literature.
- incorrect labelling by exporters and subsequently shops.
- historical over-use of some names, e.g., 'Rhinogobius wui', long treated as a synonym of R. duospilus and now recognised as a valid species.
- likely trade of undescribed species without locality data.
- mixing of species at export facilities.