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

The Siamese algae eater is a slender cyprinid from mainland Southeast Asia, found in the Chao Phraya and Mekong basins and the Malay Peninsula, in flowing streams and rivers and seasonally flooded forest. Its naming is a tangle: fish sold under the label are most often Crossocheilus oblongus, with the closely similar C. langei, the red algae eater, and C. atrilimes also traded, while the old name C. siamensis is invalid; the truly barbel-less, fringe-lipped species is rarely seen. They are prized in planted tanks as possibly the only aquarium fish that willingly eats black brush, or beard, algae, a red algae most fish refuse, though that appetite is strongest in young fish and fades as they grow and take easier food. Being a carp-family fish it is fully scaled, not scaleless, with a tan-grey back, pale belly, and a bold black stripe running from snout into the tail; the jagged edge of that stripe and the clear fins help separate it from the often-confused flying fox and the suckermouthed Chinese algae eater. It grows to around 15 to 16 cm, is an active swimmer needing room and flow, and IUCN lists C. oblongus as Least Concern.

Breeding

It is rarely if ever bred in home aquariums, and the natural reproduction is poorly known. Commercial stock is thought to come from large outdoor ponds with hormone-induced spawning, and spontaneous tank spawnings are very rarely reported. For practical purposes there is almost no home-breeding information for the species.

Common problems

Misidentification is the headline problem: Chinese algae eaters and flying foxes are constantly sold as Siamese algae eaters and neither tackles black beard algae, so it pays to learn the markings before buying. The fish jumps, so a tight lid is needed. As it grows past about 10 cm it tends to lose interest in algae and gets pushier in the tank, large and constantly active rather than truly aggressive, which can crowd a smaller setup, and some keepers move adults on at that point. It is otherwise hardy and surprisingly long-lived for an algae eater, often reaching eight to ten years, well past what many buyers expect.

Bioload

Further reading

• Algae: what kind you have and how to fix it