Simple key to species denoted as Crossocheilus siamensis,
often called Red Algae Eater or Siamese Algae Eater

By Josef Niederle
Images by Josef Niederle if not stated otherwise

My article on Crossocheilus siamensis appeared in the September 2007 issue of the Czech Akvárium terárium.
The purpose was to demonstrate the differences between the Red Algae Eater and Crossocheilus siamensis.
Fin colour shade is visible at suitable angle and illumination.
Maxillary barbels are not visible without a magnifying device.
Length means always standard length, without caudal fin.
Lateral stripe becomes paler on the head in adults.

species	obscurus added 2009	genuine oblongus	continental oblongus	langei sensu amplo	atrilimes	citripinnis nom. provis.	siamensis
lateral stripe begins at the
	apparently opercle	probably opercle	snout	snout	snout	snout	opercle
lateral line position in the lateral stripe
	straight, moved downwards	straight, central	straight, central	straight, central	convex	convex	convex
vent positioned at percent of the distance of ventral fin to anal fin bases
	70		70	70	90	90
height/length ratio
	0.24	0.2	0.2	0.2	0.25	0.25	0.2
fin colour shade
		yellow	red	brown	sandy yellow	lemon yellow ventral sometimes orange	green
eye
				honey-coloured above white below black stripe in the middle	beige above white below black stripe in the middle	beige above white below black stripe in the middle	honey-coloured without black stripe
maxillary barbels present
	no			yes	no	yes	no
black ventral blotch
	no		no	yes	no	no

To sum up, neither the Red Algae Eater nor the Lemon-finned Crossocheilus can be Epalzeorhynchos siamensis because of the presence of small maxillary barbels. Indeed, Epalzeorhynchos siamensis has no vestige of maxillary barbels according to the original description.
There are additional fundamental differences distinguishing Epalzeorhynchos siamensis alias Crossocheilus siamensis and other species.
Adult lemon-finned Crossocheilus citripinnis nom. provis. is twice as large as Crossocheilus atrilimes, about 15 cm, and pretty showy. I wonder why ichthyologists forgot to describe it. Eventually, it could be described as belonging to another genus, nevertheless it joins Crossocheilus atrilimes in aquarium.
No Crossocheilus siamensis occurs in the hobby. It is replaced by Crossocheilus langei sensu amplo, Crossocheilus atrilimes, Crossocheilus citripinnis nom. provis. and by the completely different representatives of Garra cambodgiensis alias Garra taeniata group. The latter possess broad blackish and yellowish bands in the dorsal fin. Maxillary barbels are vestigial in Garra taeniata.
The three Crossocheilus species mentioned above and Garra are marketed in large quantities, Crossocheilus langei usually in the spring. Admixtures of other species are negligible but interesting.
Comments and additional information are welcome. Use my surname followed by @math.muni.cz as the address.

Crossocheilus pseudobagroides is not identical to Crossocheilus cobitis as suggested by Bănărescu nor identical to Crossocheilus langei as suggested by Alfred. Blotches described by Duncker are still present on the holotype.
Notice added 2009 Tan & Kottelat (2009) recognize it as a separate species, and publish images of it.
See original specimens.

The colour pattern can be different in living fishes and after death as shown in Crossocheilus langei sensu amplo below.

Crossocheilus langei sensu amplo

Living and the day after
Crossocheilus langei sensu amplo is the genuine Red Algae Eater.

Crossocheilus atrilimes

Crossocheilus atrilimes is a Java Moss Eater.

Crossocheilus citripinnis nom. provis.

The Lemon-finned Crossocheilus is similar to Crossocheilus atrilimes but possesses maxillary barbels.

In Crossocheilus atrilimes and the Lemon-finned Crossocheilus the ventral region is uniformly white.

Superficially similar are other algae-eating characids and cyprinids, for example

Notropis mekistocholas

Image and identification courtesy Gerald Pottern

Apareiodon spp., sometimes as Parodon

No image available.

Crossocheilus langei sensu amplo

Black-brown lateral stripe begins at the tip of the snout and ends at the end of caudal fin. It is three scales broad, it precisely follows scale rows. Nearly straight lateral line is positioned in the centre of the stripe. During fighting the lateral stripe turns paler brown, but it doesn't change its width. Dorsal region is greyish cinnamon-coloured, the belly is white with an elongate blackish blotch around the vent. The blotch is characteristic of Crossocheilus langei. Dorsal fin is without markings. Vent is situated inside the blackish blotch approximately in the middle between the tips of ventral fins and anal fin, from which it is separated by at least two scales. A weak bronze to golden lustre on the dorsal region and occasionally a golden lustrous blotch on the head are apparent. The eye is reddish honey-coloured above and in a narrow circle around the pupil, anteriorly and posteriorly black pigmented. Its lower third is whitish. Two fleshy rostral barbels and two minute filiform maxillary barbels are present. In some specimens the maxillary barbels are visible using a magnifying glass, in others a preparation microscope is necessary. It is an excellent red-algae eater.
Notice added 2009 Confer the new remark below.

Crossocheilus atrilimes

It is a chameleon among Crossocheilus species. A black stripe begins at the tip of the snout and ends at the end of the caudal fin. It is according to the mood of the fish one to two scales broad. Its upper margin follows scale rows, but its lower margin don't. The bent lateral line reaches the lower margin of the lateral stripe at its first third. During fighting the lateral stripe turns silver-grey and broadens downwards to four scale rows so that the appearance changes substantially. It is bordered by a paler stripe above, which has a copper-coloured lustre. Dorsal region is grey-brown, sometimes darker reticulated. Belly is white. Dorsal fin is without markings. All fins are weakly sandy yellow. In classical photography they are ochre-coloured, which is confusing. Vent is positioned closely before the anal fin, from which it is separated by at most one scale. A weak copper lustre is apparent. The eye is ochre-coloured above and in a narrow circle around the pupil, anteriorly and posteriorly black pigmented. Its lower third is whitish. Two rostral barbels and no visible maxillary barbels are present. It eats red algae, but Java moss is preferred by it.

Crossocheilus citripinnis nom. provis.

Similarly shaped as Crossocheilus atrilimes. A black lateral stripe begins at the tip of the snout and ends at the end of the caudal fin. It is anteriorly two and posteriorly up to three scales broad. Its upper margin follows scale rows, but its lower margin don't. The bent lateral line reaches the lower margin of the lateral stripe at its first third. During fighting the lateral stripe doesn't change its colour or width, which is a difference to Crossocheilus atrilimes. It is bordered by a paler stripe above. Dorsal region is grey-brown. Belly is white. Dorsal fin is without markings. All fins are weakly lemon-coloured. The fin colour becomes visible with aging, ventral fins are orange in some specimens. Vent is positioned similarly as in Crossocheilus atrilimes. A weak silvery, never copper-coloured, lustre is apparent. The eye is ochre-coloured above and in a narrow circle around the pupil, anteriorly and posteriorly black pigmented. Its lower third is whitish. Two rostral barbels and two minute but distinct maxillary barbels are present. It is a further difference to Crossocheilus atrilimes. It joins Crossocheilus atrilimes in aquarium. About 150 mm SL as adult, twice as large as Crossocheilus atrilimes and pretty showy.

Inedited beginning of my original manuscript for the Aquarium Gazette which was changed by the Editors prior its publication.

Taxonomic remarks

I am not going to become an ichthyologist. But professional ichthyologists systematically publish incorrect and contradictory ad hoc views presented as scientific results. Two examples follow.

Crossocheilus oblongus and Epalzeorhynchos siamensis alias Crossocheilus siamensis are enigmatic. The names are misapplied to different species in literature. Rather recently, Kottelat first applied the latter to the taller species in Mekong basin. Later in 2000 he changed his opinion, described the species previously called Crossocheilus siamensis by him as Crossocheilus atrilimes, and considered Crossocheilus siamensis as a synonym of Crossocheilus oblongus which it of course is not. His approach is rather confusing.

The information in Bănărescu (1986) concerning Crossocheilus langei belongs to the kingdom of fairy tales. Whereas Bleeker (1860) wrote

fascia lata plusminusve diffusa fusca cephalo-caudali ...

... breeden zwarten kopstaartband

Bănărescu claimed

there is no longitudinal stripe.

It is horrible.

I would appreciate if a professional ichthyologist would publish a serious treatment of the genus. I of course provide no solutions but merely important unavoidable information which should be considered in any serious treatment.

Rostral cap margin is deeply fringed and its entire basis deeply arcuate in Epalzeorhynchos siamensis. It is negligibly fringed and shallowly arcuate in Crossocheilus langei. There are three conspicuous large pores arranged in a transversal row between the eye and the mouth in Epalzeorhynchos siamensis. No similar pores are visible in the holotype/syntype of Crossocheilus oblongus. It might be an artefact I admit. However, Bleeker (1853): 526 wrote

poris conspicuis nullis

It would be one of the fundamental differences between Crossocheilus and Epalzeorhynchos siamensis if really correct. A recollection of the latter in Tadi river in peninsular Thailand is highly desirable. It should be mentioned that, besides Epalzeorhynchos siamensis, Smith (1945): 269 collected a Crossocheilus species in Tadi river too, which he called Crossocheilus oblongus. The fishes had different vernacular names, namely pla lab mue nang being applied solely to Epalzeorhynchos siamensis. Hence not every Crossocheilus occurring in Tadi river is Epalzeorhynchos siamensis. The mouth shape of the red algae eater coincides with the mouth shape of the holotype of Crossocheilus langei.

I use the alleged holotype/syntype of Crossocheilus oblongus RMNH 2640, the lectotype designated by Alfred RMNH D1755 and RMNH D1756.
The original description of Crossocheilus oblongus by Kuhl & Van Hasselt in Van Hasselt is rather concise.

Crossocheilus Nob. is een aan Leuciscus verwant
genus, onderscheidt zich door eene naar onderen gerig-
te mondopening, in den vorm van een paralelogram; de
teekening draagt den naam van Oblongus Nob.

No details on coloration and upper lip shape are provided. It is by far not clear whether or not the interpretation by Bleeker in his Atlas is correct. The images of the alleged holotype/syntype RMNH 2640 bring little inspiration concerning coloration too. Lateral stripe starting at the opercle and containig lateral line, and a black blotch on caudal peduncle similar to Crossocheilus reticulatus are visible. Nevertheless, detailed head images illustrate fundamental differences between Crossocheilus oblongus and Epalzeorhynchos siamensis. The colour pattern of RMNH D1755 and RMNH D1756 shows lateral stripe ending on the caudal peduncle. No traces of black pigment are visible on caudal fin.
The original drawing mentioned in the description was in the possession of Bleeker and is missing now. The watercolour replica of it by Sophie D. was published in Roberts, 1993. It clearly shows a lateral stripe starting at the snout, contradicting the information in Bleeker, and ending at the caudal base.

Labeo oblongus is usually cited as a synonym of Crossocheilus oblongus. But its description by Valenciennes in Cuvier & Valenciennes is rather surprising.

Le fond général de la couleur est bleu, foncé
sur le dos et s'éclaircissant sous le ventre; la dor-
sale, l'anale et la caudale sont jaunes; les pectorales
sont orangées; les ventrales plus pâles.
J'ai fait une description à Leyde sur un
poisson long de cinq pouces; mais il paraît
que l'espèce atteint à deux pieds.

Nevertheless, it corresponds to the colour drawing by Sophie D. prepared after the original by Keultjes, Kuhl and Van Hasselt. The holotype was 5 French inches long, approximately 135 mm. In contrast, the holotype or syntype of Crossocheilus oblongus designated by Richards has approximately 75 mm SL, in my guess about 100 mm TL. Interestingly, two stuffed original specimens RMNH D1755 and RMNH D1756 are of the length indicated by Valenciennes. Bleeker alleged the following details in 1853.

colore
corpore superne coerulescente, inferne margaritaceo; fascia cephalo-cau-
dali profunde coerulea; pinnis flavescentibus vel roseis.

Habit.	Palembang, in fluviis (Van Leer)
	Buitenzorg, Tjampea, Javae insulae, in flumine Tjidani

Longitudo 4 speciminum 67''' ad 145 '''.

Mijne voorwerpen behooren stellig tot dezelfde soort
als die, welke Van Hasselt Crossocheilos oblongus noemde en
waarvan hij eene fraaije teekening naliet, welke zich in mijn
bezit bevindt en slechts van de juistheid afwijkt door een te
groot aantal schubben op eene overlangsche rei en door het
niet zigtbare van de bovenkaaksdraden.

It is not clear to me why Bleeker spoke about bovenkaaksdraden, maxillary barbels in English, instead of snuitdraden. Indeed, in the diagnosis of the genus he stated Cirri 2 rostrales. To sum up, the genuine Crossocheilus oblongus really was a blue fish with yellow fins and occured in the Cidani-Tjidani river at Ciampea-Tjampea in the vicinity of Bogor, the former Buitenzorg. There is a lot of Ci-Tji flowing from the northern slopes of Gunung Salak mountain. A recollection on Gunung Salak is highly desirable.
The Palembang specimens probably represent a different species.
Millimetre was denoted by ''' in the Netherlands since 1816.

In his original description of Crossocheilus langei Bleeker (1860) wrote

fascia lata plusminusve diffusa fusca cephalo-caudali, operculo incipiente
et basi pinnae caudalis in maculam magnam nigram transiente

In adult Red Algae Eater the stripe is unclear on the head but still detectable. Nevertheless, there are distinct chromatophores on the holotype. The problem should be solved. The Red Algae Eater might be an undescribed species too.

Remark added 2009 Tan & Kottelat (2009) published a rather serious discussion of the genus Crossocheilus occurring in Sumatra and described a new species Crossocheilus obscurus. Nevertheless, their translation of Dutch and Latin sentences is imprecise. Furthermore, the authors designated the stuffed specimen RMNH D1755 as the lectotype of Labeo oblongus, which is according to their interpretation simultaneously the lectotype of Crossocheilus oblongus designated by Alfred. By the way, RMNH 1755 as written by the authors is a completely different species Clinus cottoides according to information by Ronald de Ruiter. Surprisigly, neither the original material of Crossocheilus oblongus nor topotypes are known to the authors. It is shocking. RMNH D1755 and RMNH D1756 are in my collection of types since December 2008. Java is not a wildness, Gunung Salak is a tourist attraction. In my Czech article I spoke about Crossocheilus langei sensu Alfred. According to the image in Tan & Kottelat (2009), Crossocheilus langei sensu stricto is obviously slightly different and the remark above becomes realistic. Nevertheless, it is still the single described species sharing the features of the Red Algae Eater.

Grammatically correct is Crossocheilus nigrilobus instead of Crossocheilus nigriloba. Origin is Latin niger and Greek lobos Latinized to lobus. Crossocheilus is masculine. Crossocheilus latius is probably correct as latius should be a latinized vernacular substantive and not neutrum to latior.

There is an error in the key to the genus Crossocheilus in Smith, 1945 : 269. Correct wording is

1a Only 2 barbels, either rostral or maxillary
1b Two rostral and 2 maxillary barbels

Literature

Alfred, E. R. 1971; The Malayan cyprinid fishes of the sub-family Garrinae. Fed. Mus. J. 16: 97-103.
Bănărescu, P. 1986: A review of the species of Crossocheilus, Epalzeorhynchos and Paracrossochilus (Pisces, Cyprinidae). Trav. Mus. Hist. Nat. Grigore Antipa 28: 141-161.
Bleeker, P. 1853: Nieuwe tientallen diagnostische beschrijvingen van nieuwe of weinig bekende vischsoorten van Sumatra. Natuurkd. Tijdschr. Neder. Indië 5: 495-534.
Bleeker, P. 1860: De visschen van den Indischen Archipel, Beschreven en Toegelicht. Deel II. [Also: Ichthyologiae Archipelagi Indici Prodromus, Auct., Volumen II. [Cyprini. Ordo Cyprini. Karpers.]]. Verhandelingen der Natuurkundige Vereeniging in Nederlandsch Indië. [Also: Acta Soc. Sci. Indo-Neerl.] 7 (N. S., 2), supplement: 1-492 + i-xiii. [Also as a separate, Lange & Co., 1860.]
Bleeker, P. 1863-64: Atlas ichthyologique des Indes Orientales Néêrlandaises, ... Tome III.: 1-150, Pls. 102-144.
Cuvier, G. and A. Valenciennes 1842: Histoire naturelle des poissons. Tome seizième. Livre dix-huitième. Les Cyprinoïdes. Hist. Nat. Poiss. v. 16: i-xx + 1-472, Pls. 456-487.
Eschmeyer, W. N. 1998: (Editor) Catalog of Fishes. Center for Biodiversity Research and Information, Spec. Publ. 1. California Academy of Sciences 1-3: 1-2905. [On-line version.]
Kottelat, M. 2000: Diagnoses of a new genus and 64 new species of fishes from Laos (Teleostei: Cyprinidae, Balitoridae, Bagridae, Syngnathidae, Chaudhuriidae and Tetraodontidae). J. South Asian Nat. Hist. 5 (no. 1): 37-82.
Niederle, J. 2007: Moje anabáze s parmičkami Crossocheilus siamensis. Akvárium terárium 50 (no. 9-10): 19-23.
Niederle, J. 2009: My anabasis with red-algae eaters known as Crossocheilus siamensis. Aquarium Gazette 8: 19-31, 9: 25.
Roberts, T. R. 1993: The freshwater fishes of Java, as observed by Kuhl and van Hasselt in 1820-23. Zool. Verh. (Leiden) No. 285: 1-94
Smith, H. M. 1931: Descriptions of new genera and species of Siamese fishes. Proc. U. S. Natl. Mus. 79 (no. 2873): 1-48, Pl. 1.
Smith, H. M. 1945: The fresh-water fishes of Siam, or Thailand. Bull. U. S. Natl. Mus. No. 188: i-xi + 1-622, Pls. 1-9.
Su, R.-F., J.-X. Yang and Y.-R. Chen 2000: A review of the Chinese species of Crossocheilus, with description of a new species (Ostariophysi: Cyprinidae). Raffles Bull. Zool. 48 (no. 2): 215-221.
Tan, H.-H. and M. Kottelat 2009: The fishes of the Batang Hari drainage, Sumatra, with description of six new species. Ichthyol. Explor. Freshwaters 20 (no. 1): 13-69.
Van Hasselt, J. C. 1823: Uittreksel uit een' brief van Dr. J. C. van Hasselt, aan den Heer C. J. Temminck. Algem. Konst Letter-bode II Deel (no. 35): 130-133.

Simple key to species denoted as Crossocheilus siamensis, often called Red Algae Eater or Siamese Algae Eater