Rhinogobius formosanus OSHIMA, 1919

SynonymsTop ↑

Rhinogobius nagoyae formosanus Oshima, 1919

Etymology

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

formosanus: named for ‘Formosa’, a historic name for the island of Taiwan.

Classification

Order: Perciformes Family: Gobiidae

Distribution

This species is endemic to river systems of northern and northeastern Taiwan.

Type locality is ‘Shinchiku, Taiwan’, Shinchiku referring to a prefecture (administrative division) of the island when it was under Japanese rule and corresponding to the modern day counties of Taoyuan, Hsinchu, and Miaoli.

Maximum Standard Length

90 – 100 mm.

Aquarium SizeTop ↑

An aquarium with base dimensions of 80 ∗ 30 cm is large enough to house a small group.

Maintenance

Not difficult to maintain under the correct conditions; 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.

Water Conditions

Temperature: 18 – 28 °C

pH: 6.0 – 8.0

Hardness: 36 – 268 ppm

Diet

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.

Behaviour and CompatibilityTop ↑

This is a robust species and can be aggressive at times but it can be kept in a community provided tankmates are chosen with care.

Peaceful, pelagic species which inhabit similar environments in nature such as Tanichthys or Danio species are perhaps the best choices for the upper levels, but we’ve also seen Rhinogobius spp. being maintained alongside barbs, small characins, poeciliid livebearers, etc.

Less suitable are freshwater shrimp from genera such as Caridina and Neocaridina as these are likely to be predated upon.

Balitorid and nemacheilid loaches may prove suitable in larger tanks but in smaller set-ups R. formosanus should ideally be the only benthic species included.

It should not be mixed with congeners, especially closely-related ones, since it’s not yet clear if they’re capable of hybridisation.

Larger fishes are best omitted although in very large set-ups it may be possible to add a few non-predatory, surface-dwelling ones, while the majority of cichlids and other territorial fishes inhabiting the lower reaches should be avoided entirely.

While males are territorial with one another to an extent serious damage is unlikely provided the tank contains sufficient cover, and in fact they appear to actively require the presence of conspecifics.

Aim to purchase at least two males and as many or more females or the fish may become listless and inactive.

Sexual Dimorphism

Adult males possess more extended dorsal and anal fins, a more intensive colour pattern, and grow larger than females.

In gravid females the eggs are visible as a bluish mass through the abdomen.

Reproduction

Some wild populations of this species 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 moving into freshwater tributaries and others remaining in lower, tidally-influenced habitats.

Those exported for the aquarium trade to date appear to be entirely freshwater, however, or it may be that this species is able to reproduce in such conditions if necessary.

In nature the fish are reproductively active from summer to early autumn and during this period males begin to defend territories which tend to be centred around a flattish rock or stone beneath which the eggs are deposited, so it’s essential to provide such rocks in the breeding tank.

The eggs are very small compared with many congeners and up to 3000 or so may be deposited by a single female.

Post-spawning the female is ejected and the male assumes responsibility for brood care and guarding.

Incubation is normally 3-4 days and the larvae drift in the water column for 24 hours or so post-hatching, after which they begin to move with a greater sense of direction.

Initial food needs to be very small with freshwater rotifers or similar required until they’re able to accept Artemia nauplii and suchlike.

NotesTop ↑

R. formosanus 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 Taiwanese Rhinogobius spp. by presence of irregular, worm-like, wavy, reddish-brown lines on the cheek and opercle, and from the closely-related R. nagoyae by possessing three (vs. four) pairs of red stripes on the snout and 32-34 (vs. 34-37) longitudinal (lateral) scales.

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.

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‘ which is itself an invalid synonym of R. duospilus.
– likely trade of undescribed species without locality data.
– mixing of species at export facilities.

References

1. Oshima, M., 1919 - Annals of the Carnegie Museum v. 12 (nos 2-4): 169-328
   Contributions to the study of the fresh water fishes of the island of Formosa.
2. Chen, I-S. and K.-T. Shao, 1996 - Zoological Studies 35(3): 200-214
   A taxonomic review of the gobiid fish genus Rhinogobius Gill, 1859, from Taiwan, with description of three new species.
3. Ho, H.-C. and K.-T. Shao, 2011 - Zootaxa 2957: 1-74
   Annotated checklist and type catalog of fish genera and species described from Taiwan.