Taiwan

The genus Acrossocheilus is restricted to southern China, northern Vietnam and northern Laos. It can be distinguished from related genera by the following combination of characters: rostral fold present; lips fleshy and continuous around corners of mouth; lower lip with a median interruption; mouth inferior; horny sheath on lower jaw; two pairs of barbels; last simple ray of dorsal fin osseous with a serrated or smooth posterior margin.

This species is also known by the alternative names 'green' or 'Chinese' barb. The natural 'green' form is an infrequent find in the aquarium trade whereas the selectively-bred 'golden' variant is farmed in huge numbers and is among the most popular of freshwater aquarium fish. The latter was first produced in the 1960s and is now so ubiquitous that many hobbyists are initially unaware that it is not the natural form.

Butis spp. are largely nocturnal ambush predators with cryptic patterning to help them blend in with their surroundings. They can also lighten and darken their body colouration to an extent, have a habit of aligning themselves with solid surfaces whether horizontal, vertical, or inverted, and often swim in an upside-down position. The genus is usually included in the family Eleotridae of which members are often referred to...

An obligate dwellers of swiftly-flowing streams and headwaters containing clear, oxygen-saturated water. It inhabits riffles and runs and according to studies shows a preference for shallower zones. Substrates are generally composed of gravel, rocks, boulders or bedrock carpeted with a rich biofilm formed by algae and other micro-organisms. Aquatic plants are uncommon and while riparian/streamside vegetation may be present...

Current knowledge suggests that H. formosanus is the most widely-distributed and following Chen and Fang (2009) it can be distinguished by the following suite of characters: 3+7 dorsal-fin rays; 10-12 pectoral-fin rays (modally 11) +9-11 (modally 10)...

M. opercularis is a classic aquarium fish, having been introduced to the hobby by a French soldier named Gerault in 1869. Of the initial 100 specimens shipped, 22 survived and were successfully bred later that same year by another Frenchman, the Parisian Pierre Carbonnier. This gives the species the distinction of being one of the very first ornamental fish imported to Europe. It is also known as 'Chinese fighting fish', 'paradise gourami', and 'blue paradise fish'.

It's actually sold in the aquarium hobby on a regular basis but almost always labelled as or mixed in with Misgurnus anguillicaudatus and is thus poorly documented. Although quite simi...

Commonly known as 'Japanese rice fish' or simply 'rice fish', O. latipes is well-known to science having been widely used as a model organism in genomic and experimental biology for well over a century and was the first vertebrate animal to mate in space during the mid-1990s. It's also been a popular aquarium fish for many years, though is less widely-available than it once was, with the ornamental 'gold' vari...

This species is almost identical to the wild form of 'P.' semifasciolatus which is best known as the 'golden barb' in the aquarium hobby due to the popularity of a yellowish ornamental strain. The natural colour pattern is greenish in both species, however, and in terms of external characters they're only reliably distinguished by the fact that 'P.' semifasciolatus possesses a pair of prominent maxillary barbels wherea...

This species is normally imported alongside a smaller-growing, near-identical congener currently listed as R. cf. nantaiensis with both traded as R. candidianus. They can be separated by snout length, which is noticeably longer in R. candidianus, and adult size with R. cf. nantaiensis reaching just 50-55 mm. R. candidianus can be distinguished from other congeners by a combination of cha...

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.

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...

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 to avoid confusion we list all together here.

Presumably inhabits small rivers, tributaries and streams with substrates of gravel, rocks, boulders, and exposed bedrock which undergo seasonal variations in water flow rate, depth and turbidity. Lanyu Island is volcanic, measures just 45 km² and has no major rivers or large settlements with a permanent human population of around 4000, although there is a large nuclear waste storage facility at its southern end.

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.

This fish is normally imported alongside the congener R. candidianus and is actually the commoner of the two in the aquarium trade. It looks very similar to R. candidianus but does not grow as large and possesses a more rounded snout. Most specimens also have spot-like markings on the sides of the head which has led to them being identified as R. nantaiensis, but the fish do no...

This species occurs in a couple of colour forms with fish from northern and central Taiwan possessing a greyish base body colour and those from the Linbian river, southern Taiwan having a dark marking in the anterior portion of the first dorsal fin and larger, more intense red spots on the body. The latter form is also smaller in size, lays smaller eggs, does not exhibit extreme sexual dimorphism and has been refe...

Type locality is given as 'Boleling, northern Bali, Indonesia' which appears to correspond to modern-day Buleleng, but this species is currently understood to have a patchy but wide distribution with a range stretching westwards from the Marquesas Islands (French Polynesia), throughout much of Vanuatu, New Caledonia, the Solomon Islands, Papua New Guinea, Palau, Fiji, Indonesia, the Philippines, Japan, Taiwan, and most recently, southern mainland China...

This species is a relatively recent addition to the hobby but considering the number of specimens allowed to be collected for scientific research is highly restricted by the Taiwanese Council for Agriculture it seems odd that it's become available at all. Indeed it appears that those in the trade are collected and exported on an illegal basis (T-Y Liao, pers. comm.)...

This species is available occasionally, though not always under the correct name. We've seen it on sale as S. elegans on numerous occasions, for example, and other trade names include 'Sumatran blue neon goby' (it's not found on Sumatra), 'cobalt blue goby' and 'freshwater neon goby'. Further...

This species is rare in the aquarium trade and normally expensive when available. It's one of the most easily-identifiable in the genus by the combination of usually 14 pectoral-fin rays, 10 segmented second dorsal-fin rays, relatively small adult size, unique colouration in males and the shape of the first dorsal-fin in males in which the fourth and fifth spines are...

Wild swordtails are a fairly basic green colur. However the vast majority of swordtails available in the hobby today are hybrids of X.helleri with X.maculatus or X.variatus. There are a huge number of selectively-bred varieties available, including wagtail, lyretail, tuxedo, albino, neon, red, green and hi-fin. Swordtails may undergo what appears to be a change in sex. In young fish this may simply be late development. However some adult females develop male characteristics which is thought ...

Despite being a wholly unsuitable aquarium subject, C. idella is often traded as such, with an albino form having been developed specifically for the ornamental market. Individuals which have outgrown their aquarium or pond should never be released into natural waters, either, since this species has proven capable of causing serious environmental damage under a wide range of climatic conditions.

Members of the genus are characterised by possessing a particular number of dark vertical bar on each flank, and A. parallens belongs to a group of species with five or six such bars, each of which is two scales in width. Congeners sharing this pattern include A. fasciatus, A. hemispinus (in juveniles only), A. jishouensis, A. kreyenbergii, A. paradoxus, A. spinifer, A. wenchowensis, and A. wuyiensis.

This species is frequently confused with C. argus but can be distinguished by the following characters: dorsal-fin rays 38-45 (vs. 47-50 in C. argus); anal fin rays 26-29 (vs. 31-36); lateral line scales 50-56 (vs. 60-66); 2-3 rounded blotches on caudal peduncle (vs. no blotches on caudal peduncle). It is widely-distributed in Pacific coastal drainages of southeastern China (e.g. the Yangtze, Minjiang, Hangjiang River, and Pearl (Nanjiu...

This species can be distinguished from other members of the genus by the following combination of characters: absence of dark spots on body in adults; body elongate with slightly convex dorsal profile; head longer than body is deep; snout much longer than postorbital head length; lips well developed, lateral lobes of lower lip broad and thick with folds, median process small; barbel thickness shorter or equal to eye diameter; dorsal spine strong, ⅔ of HL; dorsal-fin origin closer to tip of snout than caudal-fin base base; 15+ gill rakers; 6½ branched anal-fin rays; posterior simple dorsal-fin rays ossified and spinous.

Widepread in eastern Asia between the Yangtze and Amur river basins, including China (mainland and islands of Taiwan and Hainan), Korea, Mongolia, Russia, and Japan. It probably been introduced to Vietnam and Laos, or records from these countries represent another species.

Although it is included in the genus Metzia this grouping remains somewhat unresolved in terms of taxonomy and it may contain more than a single genetic lineage. For example, members share a number of characters with the genera Ischikauia Jordan and Snyder 1900, Hemiculterella Warpachowski 1887, and several species of Anabarilius Cockerell 1923, including a bipartite gas bladder, a non-spinous dorsal-fin ray, and a sharp ventral keel between the pelvic-fin insertion and anus.