True Siamese Algae Eater (Crossocheilus siamensis)

The True Siamese Algae Eater (Crossocheilus siamensis); synonymous with (Crossocheilus oblongus) is a bottom dwelling member of the carp family found in the Chao Phraya and Mekong river basins in Southeast Asia and in the Malay Peninsula.

Siamese Algae Eater (Crossocheilus siamensis) is one of the most popular algae eaters used to help control nuisance algaes in planted aquariums.

True Siamese Algae Eaters are native to high flow rivers and streams, and during the rainy season, in the flooded forests. They are highly prized by tropical fish keeping enthusiasts for their algae eating abilities and their compatibility with even the most passive community aquarium fish.

The True Siamese Algae Eater has a black horizontal stripe that extends from the tip of its head all the way through the tail of the fish. The upper body of the fish is a brown/green to black/brown color with a silvery white to cream underbelly.  The horizontal stripe can fade to help camouflage the fish against its surroundings.

A True Crossocheilus siamensis has clear see through fins with the black lateral line running right to the end of the tail. They are busy swimmers that cover all levels of the water column.

A closely related species (the Red-algae eater Crossocheilus langei), is widely sold as the Siamese algae eater.   This fish has a bright brownish elongated body with a slightly flat belly and a prominent brown/black horizontal stripe that also extends from nose to the tail.   This fish can grow to over 6″ and length and has small maxillary barbels and an unfringed shallowly arcuate upper lip.

Two other similar species traded as Siamese algae eaters add to the confusion with identification, namely Crossocheilus atrilimes, a species that prefers Java Moss than red algae, and an another undescribed species of Crossocheilus.   True Siamese algae eaters are also sometimes confused with the Flying fox (Epalzeorhynchos kalopterus), the False siamensis (Garra cambodgiensis), and the Chinese Algae Eater (Gyrinocheilus aymonieri) which are all commonly sold as merely Algae Eaters.

True Siamese Algae Eaters (Crossocheilus siamensis) need a steady current and high oxygen levels to thrive in an aquarium environment.  They do not tolerate inferior water conditions with high nitrate and dissolved organics, so pristine water parameters must be maintained with regular water changes and good filtration.

They are a great fish for the community aquarium and do best in a tank with rocks, some driftwood, and that is  densely planted with broad leaved plants where the fish can rest their bodies on.  This is needed because their swim bladders are not very developed, and the fish must be in constant motion or they will sink.

True Siamese Algae Eater - Crossocheilus siamensis

True Siamese Algae Eater – Crossocheilus siamensis

True Siamese Algae Eaters (Crossocheilus siamensis) don’t lie flat on their bellies but keep their bodies propped up with their tail, pelvic, and pectoral fins.  They are occasionally found sleeping upside down.

They are strong jumpers and should not be kept in uncovered tanks because they will eventually jump out.

These fish are true algae eaters that will graze on the surface of the substrate, plants, and other aquarium decor. They are one of the few fish that feed on the nuisance “Black Beard Algae” that is a bane to some systems.

True Siamese Algae Eaters can be kept with a variety of tank mates including many of the more passive community fish.  They can be kept in a small group or preferably as a pair. Keeping them alone is an option but they prefer the company of their own kind and can be quite timid when housed alone. Do not keep them with Redtail Black Sharks as constant fighting will ensue.

The True Siamese Algae eater is one of the few fish that will tackle hair algae and even red algae.   In addition to the algae growing in the aquarium, their diet can be augmented with Spirulina flakes or algae wafers, and fresh veggies like zucchini, peas, cucumber, etc.  Although they are opportunistic feeders and will eat other foods like flakes and pellet foods; high protein diets should be avoided. They will quickly get too fat if they eat too many meaty proteins and will get lazy with the algae eating when spoiled with too much commercial food. But since they have a very high metabolism, keeping them from high protein commercial foods for 2 to 3 days will get them back to a straight algae diet.

Because sexing is only possible in mature specimens, True Siamese Algae Eaters are extremely difficult to accurately sex. Generally the gravid females will have a rounder belly than the males but when well fed, males also have round bellies, which is probably why no breeding has yet been documented in an aquarium environment.   In addition, gravid females have the ability to reabsorb their eggs when not fertilized.

Because of the similarity to others in its genus,  considerable confusion exists with many tropical fish shop proprietors with their identification however, a true Siamese Algae Eater has clear see through fins and a black serrated stripe that runs all the way to the tip of the tail.   Although the “true” Crossocheilus siamensis is not often available to tropical fish keeping enthusiasts, when they are available their approximate purchase size is between 1-1/4″ to 2-1/2″.

True Siamese Algae Eater - Crossocheilus siamensis

True Siamese Algae Eater – Crossocheilus siamensis








Minimum Tank Size: 30 gallons
Care Level: Easy
Temperament: Peaceful
Aquarium Hardiness: Hardy
Water Conditions: 72-82° F, KH 5-15, pH 6.5 – 8.0
Max. Size: 6.2 ”
Color Form: Black, White
Diet: Omnivore
Compatibility: Good community tanks
Origin: Asia, Thailand, Indonesia
Family: Cyprinidae
Life Span: 10 years
Aquarist Experience Level: Beginner

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