Siamese algae eater

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Feeding

Eats black beard algae, hair algae, and other filamentous algae that most fish ignore. This is the main reason people buy them. However: SAEs become lazier about eating algae as they age and grow, especially if they have access to easier food. An SAE that's fed sinking pellets every day will stop bothering with tough BBA. Some keepers recommend underfeeding to maintain algae-eating motivation, but this should be done carefully. Supplement with blanched vegetables and algae wafers. SAEs also eat flatworms (planaria) and hydra, which is a useful bonus.

Compatibility

• Generally peaceful but becomes more boisterous with age. Juveniles are calm; adults can be pushy toward slow-moving bottom-dwellers.
• Fast swimmer that may stress timid tankmates with constant activity.
• Occasionally chases other SAEs and similarly-shaped fish. Territorial behavior increases with size.
• Works well in planted tanks with robust tankmates: tetras, barbs, rainbowfish, corydoras.
• May eat moss (java moss, christmas moss) if hungry. Not reliably plant-safe in all situations.

Origin and habitat

Native to mainland Southeast Asia. Found in the Chao Phraya and Mekong basins as well as the Malay Peninsula; also reported from Cambodia, Laos, and possibly the Indonesian islands of Sumatra and Borneo. Inhabits flowing streams and rivers, and flooded forests during the rainy season. The taxonomy of "Siamese algae eaters" in the trade is complicated: fish sold under this label are most often Crossocheilus oblongus (described by Kuhl and van Hasselt, 1823), though C. langei and C. atrilimes also appear; all behave similarly as algae eaters. The true C. siamensis, which lacks maxillary barbels and has a deeply fringed V-shaped upper lip, is rarely encountered in the trade. Valued in planted aquariums because it is one of the few fish that willingly eats brush/beard algae, though this appetite is strongest in younger fish and diminishes with age as they increasingly prefer other foods. Often confused with the flying fox (Epalzeorhynchos kalopterus); the SAE can be distinguished by its jagged-edged lateral stripe (vs straight on the flying fox) and stockier body. Grows to about 15–16 cm. An active swimmer that needs a tank of at least 100 liters, with good water flow and oxygenation. IUCN Least Concern for C. oblongus.

Breeding

Not bred in captivity. All SAEs in the trade are wild-caught. No successful hobby breeding has been documented. The reproductive biology in the wild is poorly understood. This is one of the few popular aquarium fish with zero breeding information available.

Common problems

Misidentification is the biggest issue. Chinese algae eaters and flying foxes are frequently sold as SAEs, and they don't eat BBA. Learn the visual differences before buying. SAEs jump; a tight lid is mandatory. As SAEs grow past 10 cm, they become less interested in algae and more disruptive in the tank. Some keepers rehome them at this point. They're not aggressive enough to cause damage but their constant swimming and size can dominate a smaller tank. Lifespan is 8-10 years, which is longer than most people expect from an "algae eater" purchase.

Bioload

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size