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Algae Eating Cyprinids from Thailand and Neighboring Areas

Neil Frank and Liisa Sarakontu
Photographs by Neil Frank
Illustrations by Liisa Sarakontu

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This article talks about five fishes from Thailand and neighboring areas, including the elusive Siamese Algae Eater (Crossocheilus siamensis) which is the only known fish to effectively eat red beard/brush algae (Audouinella). The other four fishes are (1) a very similar fish which we call the false siamensis, (2) a more colorful relative - the Flying Fox (Epalzeorhynchus kalopterus), (3) another Crossocheilus species and (4) the Chinese algae eater (Gyrinocheilus aymonieri). To the casual observer, all fish may look the same at first. Even some reputable aquarium texts have confused the real and false siamensis. A summary table is included at the end to compare the distinguishing features among these interesting fishes. Information is also presented on the availability of the Siamese Algae Eater in Europe and America and on ways to purchase this fish.

Siamese Algae Eater

Siamese Algae Eater
Siamese Algae Eater, Crossocheilus siamensis (Smith, 1931).

This slender algae eating barb is the only known fish that eats red algae. It comes from the flowing waters of Thailand and the Malay peninsula. It was first brought to Europe in 1962, but became popular in the 1970's when its ability to eat red algae was noticed. The fish is also known as Siamese Flying Fox, and Siamese Fox. It previous scientific name was Epalzeorhynchus siamensis. To those interested in the fine, but admittedly boring details of taxonomy, the genus Crossocheilus differs from Epalzeorhynchus by rhynal lobes (nasal lobes).

Description: It is a slender, grayish-brown fish with a distinctive black horizontal stripe. Maximum length is 15 cm (6 inches) and might be obtained in two years, if the conditions are optimal. Normally they grow slower and don't always reach that size in captivity. They can live over 10 years. All the fins are transparent or slightly milky without any yellow or reddish sheen. The black band goes from nose to the fork of the tail and its edges are zig-zagged. When a fish is stressed or fighting the black color fades significantly. Underparts are silvery white and there is no light stripe over the black, but the whole upper body is brownish and every scale has a dark edge, which make the top look reticular. Some dark scale edges might be seen under the black stripe. It has two pairs of thin, forward-pointing barbels but they might be pressed against the cheeks when fish is swimming or resting. The long black stripe is also easy to see in young fishes, but the scale edge pattern and zig-zag edges are not clearly visible until the fish reaches the length of 5-7 cm (2-3 inch); the ones that are normally seen in European shops are about 3-5 cm (1-2 inch) long. Adult females are often slightly fatter than males, no other sexual differences are known.

Behavior: It is an active and fast swimmer, which thrives best in schools but can also be kept alone or in pairs. It is a strong jumper and should not be left unattended in small uncovered containers. Siamese Algae Eaters often chase one another, but they never get hurt in these fights. It doesn't bother any of its tankmates.

C. siamensis has a peculiar resting position: it doesn't lie flat on its belly but keeps its body propped up with its tail, pelvic and pectoral fins. Young fish sometimes rest on broad leaves, adult specimens prefer resting on bottom or dense, low plants like Cryptocorynes. The swim bladder is not very developed, so the fish can't stay in midwater but it must be in constant motion or it sinks.

Needs: Siamese Algae Eater is not very demanding. Suitable temperature is 24-26 C (75-79F). They can tolerate pH from 5.5 to 8.0, but 6.5-7.0 is ideal. Hardness should be less than 20 dH. Water should be clean and oxygenated, because they come from bright and fast-flowing streams. They eat algae, including red algae and all kind of live and prepared foods. It is very rare that they harm plants in their tank if they are given enough green food. They also eat algae when they are mature, but seem to prefer flake food. Liisa's fish eat Duckweed (Lemna minor) but have never touched any other plants. They haven't yet been bred in captivity, so all the specimens are caught from nature. It appears that the fish are seasonal and are not always available in the shops. Minimum tank size for a pair of adult Siamese Algae Eaters is 100 liters (25 gallons). The aquarium should be long and have lots of living plants.

Compatibility: As they are not aggressive, they can be kept in any community tank big enough. Their active behavior might stress some sensitive species like dwarf cichlids and prevent them from spawning. They should not be kept with Red-tailed Sharks (Epalzeorhynchus bicolor) unless the aquarium is large and well planted, because that species is very aggressive towards all its relatives.

Availability in the Aquarium Trade: The Siamese Algae Eater, Crossocheilus siamensis is quite common in Europe. In fact, it is one of the top ten fish sold in Finland. Although it became known to the American hobbyist in the 1980's through the translation of European literature, most notably The Optimum Aquarium, the fish has been virtually absent from the American aquarium scene. This might be attributed to several factors. First, some English language books did not publish the correct picture of the true SAE. These include the English edition of the Baensch Atlas, Volume I (same as the first German edition of this Volume) and the early editions of the Axelrod Atlas. In these books, the illustrated fish is the false siamensis, Garra taeniata or another Epalzeorhynchus species. Secondly, the true SAE is thought to be less colorful than several of its relatives. In fact, in some countries of Asia (e.g. Taiwan), this fish is known as one like flying fox; the fish we call false siamensis is known as colorful flying fox.

Now, we know about at least 2 suppliers of this fish in the U.S. -- The Albany Aquarium, an aquarium store in Albany, CA, imports them directly from Southeast Asia. They were willing to ship Overnight Federal Express directly to hobbyists.

Contact: Albany Aquarium, 818 San Pablo Ave., Albany, CA 94706, (510) 525-1166

Southern Tropical Fish, a tropical fish wholesaler in Lakeland, Florida is currently importing them from Bangkok. The fish first showed up on the wholesale listing as small flying fox. After we discussed the differences among the related species with this firm, the identity crisis is no longer a problem. The true SAE are now regularly appearing in North Carolina and elsewhere in the Eastern U.S. Ask your local aquarium store to contact Southern Tropicals to see if they can acquire this red algae eating fish for your area.

False Siamese Algae Eater

False Siamensis
False siamensis (Epalzeorhynchus sp. or Garra taeniata)

This algae eating barb strongly resembles the Siamese Algae Eater. It comes from the same region and at least young specimens can school together. These fish are often mistaken for real Siamese Algae Eater. In Finland, it is common to see some specimens among a tankful of Siamese Algae Eaters. Up until now, it seems that the real Siamese Algae Eater has been a rarity in U.S., and the false siamensis is often sold as Siamese Algae Eater. More confusing is that many respected Aquarium books (e.g. Baensch Atlas, Volume 1, english edition) present this fish as the Siamese Algae Eater (Crossocheilus siamensis). This fish has also been sold as the Thailand Flying Fox. There is still some uncertainty regarding the true identity of this fish. Markku Varjo states that it is the Siamese Stone Lapping Fish (Garra taeniata Smith 1931), but other very knowledgeable aquarists (including Heiko Bleher and Fumitoshi Mori) believe it is some species of Epalzeorhynchus.

Description: At first sight this fish is just like the Siamese Algae Eater, but they are easy to tell apart when you know what to look. The black horizontal band does not go to the fork of the tail but stops at the base of the tail and its edges are rather smooth. When the fish is frightened the black stripe fades to light grey. All fins except pectoral are yellowish and there are dark markings on the dorsal fin. The rays near the base of the dorsal fin are black and there is another dark band in the upper part of dorsal. There is a distinctive narrow light stripe over the black horizontal band and the dorsal region is solid grayish brown without dark scale edges. The top area is also slightly darker than Siamese Algae Eater. Sometimes bright red or pink is seen around the mouth but it might disappear if the fish is stressed. It has two pairs of barbels (like the Siamese Algae Eater). Maximum length is reported to be 15 cm (6 inch). No sexual differences are known, but the amount of red might depend on the sex of the fish. In the orient, these fish are called colorful flying fox. Ironically, Crossocheilus siamensis is called the one like flying fox. Behavior. Adult specimens are aggressive towards each other, otherwise like Siamese Algae Eater.

Needs: False siamensis is more demanding on water quality than Siamese Algae Eater. It needs very clear and oxygenated water, ideal temperature is 24-26 C (75-79F) and the pH shouldn't get much under 7. They eat some algae, but in nature they probably seek small animals from algae growths. In aquarium they eat all kinds of live and artificial foods. They have not been bred in captivity. Minimum tank size for it is 80 liters (20 gallons).

Compatibility: Can be kept in any community tank. Adult specimens often get aggressive toward each other, so there shouldn't be more than one false siamensis in a tank. They might also harass related species and other small bottom-dwellers like loaches, if the tank is not big enough.

Flying Fox

Flying Fox
Flying Fox, Epalzeorhynchus kalopterus (Bleeker, 1850)

The Flying Fox is the most colorful of this fish group. For this reason, it has gained popularity in the U.S. over Crossocheilus siamensis and false siamensis. It comes from the flowing waters of Thailand, Sumatra and Borneo. Wholesalers sometimes deliver this species as Siamese Algae Eater in Finland. This fish is also known as Trunk Barb.

Description: Body and fin shape like two previous species. Thin specimens are often pictured in the aquarium literature. The overall color is warmer brown or even goldish and the black horizontal stripe goes from nose to the fork of the tail like on Siamese Algae Eater, but the part going through the tail fin in darker and broader. There is a narrow golden stripe over the black. Dorsal, anal and pelvic fins have indistinctive dark bands and bright white tips. It has 2 pairs of barbels. Maximum length is reported to be 15 cm (6 inch). No sexual differences are known.

Behavior: Same as previous species. Adult specimen is territorial and aggressive towards its own kind.

Needs: Ideal pH is near 7, temperature 24-26C (75-79F). It eats all kinds of live, prepared and plant foods. It has not been bred in captivity. Minimum tank size 80 liters (20 gallons).

Compatibility: Flying Fox can be kept in a community tank, but it might chase other fish viciously from its territory. There shouldn't be more than one adult Flying Fox in a tank.

Crossocheilus oblongus(Cuvier and Valenciennes, 1842)

This is a close relative to Siamese Algae Eater, and it is possible that specimens of this fish are sometimes found in schools of Siamese Algae Eater or false siamensis.

Description: Body shape and color are basically same as Siamese Algae Eater and false siamensis. All the fins are transparent and the black horizontal stripe does not extend to the tail fin. The stripe has smooth edges and the back is solid, not reticulated like on Siamese Algae Eater. It has two pairs of barbels like Flying Fox. Maximum length is 10 cm (4 inch).

Behavior, needs and compatibility: Probably same as previous three species.

Chinese Algae Eater, Gyrinocheilus aymonieri (Tirant, 1883)

This Algae Eater belongs to family Gyrinocheilidae, although it resembles both loaches and Algae Eating barbs. Its English name isn't very accurate, because it comes from Northern India and Thailand, not China. It is also called the Indian Algae Eater. There are still some unclear points in the systematic classification of this genus and it is possible that the species most often imported isn't G. aymonieri but G. kaznakovi. There are also two other species (G. pustulosus and G. pennocki).

Description: Chinese Algae Eater is a bottom-dweller. The most prominent feature is a big suckermouth, which it uses for scraping algae and clinging to objects. There is a special opening on the upper part of the gill cover for the water intake so the fish can breath without using its mouth. This same feature is seen on Suckermouth Catfishes. The fish is light brown and there is a dark grey or brown horizontal pattern on its side, which can be either a zig-zag edged solid stripe or a row of separate spots or anything between these two. Young specimens are more colorful. There are some dark patches at the back and small brown spots at the tail. All the other fins are transparent or slightly brownish. Maximum length is 27 cm (11 inch) but normally it doesn't exceed 15 cm (6 inch) in an aquarium. Females are larger and fuller, adult males might show spawning tubercles on the head.

Behavior: It moves along all the surfaces of the tank scraping green algae with its suckermouth. Older specimens prefer artificial foods and are rather aggressive.

Needs: Chinese Algae Eater is not very demanding on water conditions: pH may vary from 6.0 to 7.5 and the temperature from 22C (72F) to 28C (82F). Water should be well oxygenated, as it comes from streams. It eats all kinds of foods, but must get enough algae or plant food. It is reported that it will stop eating algae if the temperature drops below 69 degrees F (20 deg. C). It has not been bred in captivity. Minimum tank size 100 liters (25 gallons).

Compatibility: Young Chinese Algae Eaters can be kept in community, but adult specimens can be aggressive to other fish. They most often attack slow-swimming, flat-bodied fish and shouldn't be kept with them.

Distinguishing Features of Algae Eating Cyprinids

Crossocheilus siamensis False siamensis Epalzeorhynchus kalopterus Crossocheilus oblongus Gyrinocheilus aymonieri
Horizontal stripe
zig-zag smooth smooth smooth uneven
-extend to tail: yes no yes no
light stripe above (sometimes) yes yes ?
Dorsal region: reticulated (black edged scales) solid greyish brown
- dorsal:
transparent dark lower rays & yellowish dark bands & white tips transparent transparent
- anal: yellowish
- pelvic:
Mouth: small, nonclinging suckermouth (maybe with red/pink) clinging suckermouth
Barbels: 2 pairs 2 pairs 2 pairs 2 pairs none

1/2005: Added correction for number of barbels (2 pairs for SAE)—EO. Also note that the row starting with light stripe above reflects the correct data, which was misprinted in TAG.


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Mills, D. et al 1988: Tropical Aquarium Fishes. Tetra Press, NJ.
Petrovicky, I. 1988: Aquarium Fish of the World. Arch Cape Press, New York.
Riehl, R. and Baensch, H.A. 1989: Aquarium Atlas (Volume 1), MERGUS, Germany.
Smith, H.M. 1945: The Fresh-water Fishes of Siam, or Thailand, Bulletin 188. Smithsonian Institute, Washington D.C.
Varjo, M. 1989: Akvaariomaailma. - WSOY. Porvoo.
Varjo, M. 1983: Levabarbi vai mika? Akvaariolehti 3/83:16-19.