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Erromyzon sp. 'ER02'


Erromyzon: from the Latin erro, meaning ‘to wander, err, go the wrong way, make an error’, and Greek μύζω (myzo), meaning ‘to suckle’.


Order: Cypriniformes Family: Gastromyzontidae


It’s range is unclear but this fish is native to southern China and tends to be imported alongside Beaufortia, Pseudogastromyzon or Rhinogobius spp. from that region.


Erromyzon spp. are obligate dwellers of shallow, fast-flowing, highly-oxygenated headwaters and minor tributaries characterised by stretches of riffles and runs broken up by pools or cascades in some cases.

Substrates are normally composed of smaller rocks, sand and gravel with jumbles of boulders, and while riparian vegetation and patches of submerged leaf litter are common features aquatic plants aren’t usually present.

The most favourable habitats contain clear, oxygen-saturated water which, allied with the sun, facilitates the development of a rich biofilm carpeting submerged surfaces.

During periods of high rainfall some streams may be temporarily turbid due to suspended material dislodged by increased (sometimes torrential) flow rate and water depth.

Maximum Standard Length

45 – 50 mm.

Aquarium SizeTop ↑

An aquarium with base dimensions of 60 ∗ 30 cm should be the smallest considered.


Most importantly the water must be clean and well-oxygenated so we suggest the use of an over-sized filter as a minimum requirement.

Turnover should ideally be 10-15 times per hour so additional powerheads, airstones, etc. should also be employed as necessary.

Base substrate can either be of gravelsand or a mixture of both to which should be added a layer of water-worn rocks and pebbles of varying sizes.

Aged driftwood can also be used but avoid new pieces since these usually leach tannins that discolour the water and reduce the effectiveness of artificial lighting, an unwanted side-effect since the latter should be strong to promote the growth of algae and associated microorganisms.

Exposed filter sponges will also be grazed can represent a useful additional food source.

Although rarely a feature of the natural habitat aquatic plants can be used with adaptable genera such as MicrosorumCrinum and Anubias spp. likely to fare best. The latter are particularly useful as their leaves tend to attract algal growth and provide additional cover.

Since it needs stable water conditions and feeds on biofilm this species should never be added to a biologically immature set-up, and a tightly-fitting cover is necessary since it can literally climb glass.

While regular partial water changes are essential aufwuchs can be allowed to grow on all surfaces except perhaps the viewing pane.

Water Conditions

Temperature18 – 24 °C

pH6.5 – 8.0

Hardness36 – 268 ppm


Much of the natural diet is likely to be composed of benthic algae plus associated micro-organisms which are rasped from solid surfaces.

In captivity it will accept good-quality dried foods and meatier items like live or frozen bloodworm but may suffer internal problems if the diet contains excessive protein.

Home-made foods using a mixture of natural ingredients bound with gelatin are very useful since they can be tailored to contain a high proportion of fresh vegetables, Spirulina and similar ingredients.

For long-term success it’s best to provide a mature aquarium with a plentiful supply of algae-covered rocks and other surfaces.

If unable to grow sufficient algae in the main tank or you have a community containing numerous herbivorous fishes which consume what’s available quickly it may be necessary to maintain a separate tank in which to grow algae on rocks and switch them with those in the main tank on a cyclical basis.

Such a ‘nursery‘ doesn’t have to be very large, requires only strong lighting and in sunny climates can be kept outdoors. Algal type is also important with diatoms and softer, green varieties preferred to tougher types such as rhodophytic ‘black brush’ algae.

Gastromyzontids are often seen on sale in an emaciated state which can be difficult to correct. A good dealer will have done something about this prior to sale but if you decide to take a chance with severely weakened specimens they’ll initially require a constant source of suitable foods in the absence of competitors if they’re to recover.

Behaviour and CompatibilityTop ↑

Largely peaceful although its environmental requirements limit the choice of suitable tankmates somewhat, so research your choices before purchase in order to be sure.

Species inhabiting similar natural waters include Barilius, Garra, Devario, some Rasbora, Rhinogobius, Sicyopterus and Stiphodon gobies plus catfishes like Glyptothorax, Akysis and Oreoglanis.

Many loaches from the family Nemacheilidae, Balitoridae and Gastromyzontidae are also suitable although harmless squabbles may occur with the latter group in particular.

Like many loaches it’s loosely territorial towards conspecifics but seems to require their presence to truly thrive. A group of four or more specimens should be the smallest considered.

Sexual Dimorphism

Undocumented as far as we’re aware but larger, heavier-bodied specimens are likely to be female.


This species has been bred in captivity by German aquarist Gerhard Ott although it was identified as E. sinensis at the time.

Nuptial males were observed to select a particular spot, usually a vertically-inclined rock face, which was then defended against rivals.

When a receptive female entered this temporary territory a complex series of communicative movements was observed with the pair ending in a ‘T’ shaped position whereby one fish was seen to stimulate the genital area of the other using the mouthparts.

During the spawning event itself both fish inserted the rear portion of the body and caudal fin into the substrate at which point the eggs were released and simultaneously fertilised.

As in some related genera such as Pseudogastromyzon there was no additional broodcare and the fry spent the early part of life concealed within the substrate, exhibiting a strongly photophobic reflex if exposed.

They began to emerge at a size of around 10 mm TL and were fed on sinking tablet foods with daily water changes of 75% tank volume performed during the initial period. Even with these measures in place significant differences in growth rate between individuals was apparent.

The fish spawned three times consecutively but after that no reproductive behaviour was observed until they died one-by-one, possibly due to excessively high water temperatures.

The author also experimented with substrates by placing bowls containing gravel of different grades in the tank and found that a grain size of 1.5 – 3.5 mm was preferred with larger types ignored.

NotesTop ↑

This fish remains in need of identification, and we’ve chosen to list unidentified members of the genus using an ‘ER’ numbering system in the absence of definitive information.

Trade names include Erromyzon sp. ‘red spots’ or ‘Strawberry Spot Sucker Loach’ and it’s also been identified as a Gastromyzon or Pseudogastromyzon sp. on occasion.

It’s quite easy to distinguish from congeners since it’s the only species known to possess a colour pattern comprising a dark base colour and series of thin, paler vertical bars on the body and similarly-coloured spots on the head.

Older individuals also develop a series of red spots along the lateral line, each of which is located within one of the pale vertical bars, a character also observed in the congener E. kalotaenia.

E. sinensis, the type species of the genus, was initially included in the genus Protomyzon where it remained until 2004 when Kottelat found sufficient geographical and morphological differences between members of the group inhabiting the island of Borneo and those from mainland East and South East Asia to warrant their separation.

The genus Erromyzon was erected to accommodate the mainland fishes and there are currently three recognised members with at least one awaiting description (Neely, pers. comm.).

Members are told apart from other balitorids by the following combination of characters: gill opening small and positioned entirely above the base of the pectoral finopercle not distinct being absent or forming an indistinct groove between the gill opening and base of pectoral-fin; possession of 1 simple and 17-20 branched pectoral-fin rays; 1 simple and 6-8 branched pelvic-fin rays; pelvic fins are not fused; upper lip and rostral fold not fused; upper lip runs continuous with lower but there is a small notch just before each corner of the mouth; rostral fold has 4 notches to contain the rostral barbels; lower lip does not extend beyond the corners of the mouth; postlabial groove extensively interrupted with the space inbetween the anterior extremities forming a rectangular-shaped, fleshy pad.

Erromyzon can be told apart from Protomyzon by the fact that the gill opening is reduced to a small slit just above the base of the pectoral fins and it lacks a visible opercle (vs. visible opercle); both upper and lower lips run continuously around the corners of the mouth (vs. interrupted), and don’t “form an arched-blade-like structure” (vs. forming); the lower lip is smooth (vs. papillated).

The family Gastromyzontidae is currently considered valid as per Kottelat (2012).

It contains a number of genera which had formerly been included in several families and subfamilies, most recently Balitoridae, of which the most well-known in the aquarium hobby include Beaufortia, Formosania, Gastromyzon, Pseudogastromyzon, Hypergastromyzon, Liniparhomaloptera, Sewellia and Vanmanenia.


  1. Kottelat, M., 2004 - Ichthyological Exploration of Freshwaters 15(4): 301-310
    On the Bornean and Chinese Protomyzon (Teleostei: Balitoridae), with descriptions of two new genera and two new species from Borneo, Vietnam and China
  2. Kottelat, M., 2012 - Raffles Bulletin of Zoology Supplement 26: 1-199
    Conspectus cobitidum: an inventory of the loaches of the world (Teleostei: Cypriniformes: Cobitoidei).
  3. Neely, D. A., K. W. Conway, and R. L. Mayden, 2007 - Ichthyological Exploration of Freshwaters 18(2): 97-102
    Erromyzon yangi, a new hillstream loach (Teleostei: Balitoridae) from the Pearl River drainage of Guangxi Province, China.
  4. Tan, H. H., 2006 - Natural History Publications (Borneo), Kota Kinabalu: 1-245
    The Borneo suckers. Revision of the Torrent Loaches of Borneo (Balitoridae: Gastromyzon, Neogastromyzon).
  5. Tang, Q., H. Liu, R. Mayden and B. Xiong, 2006 - Molecular Phylogenetics and Evolution 39(2): 347-357
    Comparison of evolutionary rates in the mitochondrial DNA cytochrome b gene and control region and their implications for phylogeny of the Cobitoidea (Teleostei: Cypriniformes).
  6. Šlechtová, V., J. Bohlen and H. H. Tan, 2007 - Molecular Phylogenetics and Evolution 44(3): 1358-1365
    Families of Cobitoidea (Teleostei; Cypriniformes) as revealed from nuclear genetic data and the position of the mysterious genera Barbucca, Psilorhynchus, Serpenticobitis and Vaillantella.

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