Crossocheilus langei
The legendary BBA eater. True Crossocheilus oblongus has a single solid black horizontal stripe extending into the tail; lookalikes (false SAEs, flying foxes) have either broken stripes or coloured fins. Buy from a knowledgeable source, misidentification is rampant in chain stores.
Siamese Algae Eater (Crossocheilus langei) reaches 12–15 cm as an adult and needs a minimum tank of 150 L. Native to Mainland Southeast Asia (Thailand, Malaysia, Indonesia), it lives in the bottom (grazes everywhere) water column with a peaceful (becomes mildly territorial as adult) temperament. Aim for 24–28 °C, pH 6.5–7.5, and 5–15 dGH hardness. Lifespan is 8–10 years with good care. Keep siamese algae eater in groups of 4+, loose group schoolers need numbers to display natural behaviour. Diet: omnivore (heavy algae grazer), Algae, biofilm, blanched veg, sinking pellets, occasional protein. Will eat dreaded black beard algae, one of very few fish that do. Plant-safe: Yes. Shrimp-safe: Yes (adults safe with adult shrimp).
Care at a glance
The legendary BBA eater. True Crossocheilus oblongus has a single solid black horizontal stripe extending into the tail; lookalikes (false SAEs, flying foxes) have either broken stripes or coloured fins. Buy from a knowledgeable source, misidentification is rampant in chain stores.
By Mike ElmiraUpdated 2 min read
Part of our complete guide to aquarium fish for the planted tank.
Hero photo by aleander2137 · CC BY-SA 4.0 · Wikipedia
The parameters that decide whether siamese algae eater fits in your tank.
Bottom (grazes everywhere)
No
Small group of 4+
Cyprinidae
Omnivore (heavy algae grazer)
Algae, biofilm, blanched veg, sinking pellets, occasional protein. Will eat dreaded black beard algae, one of very few fish that do.
8–10 yrs
Very hard
Fast-flowing forest streams across mainland Indochina
Mainland Southeast Asia (Thailand, Malaysia, Indonesia)
Tank-mate safety and the species this one is documented to thrive (or fail) alongside.
Most medium-sized community fish. Tetras, rasboras, gouramis, peaceful cichlids. They become mildly territorial with their own kind as adults — keep 4+ in a large tank to dilute aggression.
Other 'algae eater' species (territorial overlap), very small nano fish (SAEs can be boisterous adults), shrimp colonies (they'll eat shrimplets and may chase adults).
Hard-won lessons from the tank.
The ONLY common community fish that reliably eats black beard algae. Add 1–2 young SAEs to a BBA-affected tank and within weeks the BBA is consumed. Once the tank is clean, SAEs may stop eating BBA and switch to easier foods — but the existing BBA is gone. Keep them well-fed with sinking veg wafers so they don't develop a taste for plant leaves.
Genus 'Crossocheilus' = 'fringed lip' (referring to the unusual mouth structure). Species 'oblongus' = 'elongated'.
What can go wrong and how to spot it.
Failure modes, in order of how dramatic the fix is.
Robust. Watch for ich during transport.
ID disasters are everywhere in chain stores. The 'false SAE' (Garra cambodgiensis) doesn't eat BBA. The flying fox has red fin tips and a black-edged dorsal. The Chinese algae eater is a different family entirely and becomes aggressive as an adult.
The practical routine, read top to bottom.
150 L+ for adults. Open swimming space (they're active swimmers). Smooth rocks for grazing surfaces. Driftwood. Moderate flow with good oxygenation. They jump — tight-fit lid required.
3 weeks.
Where it comes from, how it behaves, and the variants you'll see at retail.
Where it lived before it came home.
Slow streams and rivers across mainland Southeast Asia. Sandy and rocky substrate with abundant submerged vegetation and biofilm-covered surfaces.
Algae (including hair algae and BBA), biofilm, fallen invertebrates, plant matter.
Habitat loss is a concern in some regions. Captive-bred stock dominates the trade.
How they pair, reproduce, and grow.
Females slightly fuller-bodied when mature; males slimmer. Difficult to sex with confidence outside breeding condition.
Almost never bred in home tanks. Commercial stock is farmed via hormone induction in Southeast Asian fish farms.
The named cultivars and the lookalikes worth flagging.
True wild type only. Frequently confused with the 'false SAE' (Garra cambodgiensis), 'flying fox' (Epalzeorhynchos kalopterus), and 'Chinese algae eater' (Gyrinocheilus aymonieri). True C. oblongus has: a single solid black stripe extending through the caudal fin, transparent fins (no red/yellow tips), and a slightly forked tail.
Direct answers to the questions search engines and AI assistants surface most often about this species.
Siamese Algae Eater (Crossocheilus langei) needs a minimum tank of 150 L. They live in the bottom (grazes everywhere) water column and should be kept in groups of 4+, so a longer footprint matters more than depth.
Target 24–28 °C, pH 6.5–7.5, and 5–15 dGH hardness. Acclimate slowly when moving them between water sources.
Shrimp safety: Yes (adults safe with adult shrimp). Plant safety: Yes.
Siamese Algae Eater are omnivore (heavy algae grazer). Algae, biofilm, blanched veg, sinking pellets, occasional protein. Will eat dreaded black beard algae, one of very few fish that do.
On Fin & Stem's 1–5 difficulty scale this species rates 2/5. Forgiving, beginner-friendly once the tank is cycled. Breeding difficulty: very hard.
Typical lifespan in a well-maintained tank is 8–10 years.
A planted tank is a system. Pair this fish with one entry from each other pillar to plan the whole scape.
