Siamese algae eater vs Chinese algae eater: how to tell them apart

Are they the same fish?

No. They're different genera — Crossocheilus for the Siamese algae eater, Gyrinocheilus for the Chinese algae eater — sold under overlapping trade names, displayed side by side in shops at a similar small juvenile size, and genuinely difficult to tell apart at that size without checking specific features. The confusion is well documented in specialist hobbyist literature and runs in one particular direction more often than the other: shops have been documented selling Chinese algae eaters under the Siamese algae eater name to buyers who specifically asked for the calmer, more consistently peaceful species[1].

This isn't a minor identification footnote. As adults, the two diverge in ways that matter for stocking a tank responsibly — size, temperament, group tolerance and whether algae remains a meaningful part of the diet all differ, covered section by section below.

Side-by-side comparison

None of the figures in this table are new research — every one traces back to our Siamese algae eater or Chinese algae eater care guide, where the full sourcing and the "what we deliberately left out" caveats already live. A correction to any underlying fact only needs making once, in the species guide, rather than in two places at once.

Telling them apart: what to look for

Four checkable features do most of the work, and none of them require specialist equipment — just a close look before you buy, or a careful look at a fish you already own[2][3]:

• The stripe. A genuine Siamese algae eater's black stripe runs unbroken from the tip of the snout all the way through the tail fin. If it stops short of the tail, or the fish's pattern doesn't resemble a single continuous stripe at all, you're likely not looking at this species.
• The fins. A genuine Siamese algae eater's fins are plain, without red, orange or black edging. Coloured fin edging points toward a different, related fish (most often a flying fox) rather than either species compared here.
• The mouth. A Chinese algae eater has a distinctive ventral sucker mouth, used to grip surfaces while grazing and, later, to attach to a tankmate during slime-feeding. A Siamese algae eater's mouth doesn't have this pronounced sucker form.
• Body shape and size at a given age. A Chinese algae eater tends toward a more elongated, thicker-bodied adult than the slimmer, torpedo-shaped Siamese algae eater, though this is less reliable on very young juveniles than the stripe and mouth checks above.

If you're checking a fish you already own rather than one you're about to buy, the same four checks apply equally well — there's no special "already in my tank" version of the identification process.

Scientific names and the common-name confusion

The Siamese algae eater's own scientific name has shifted over time: the name most hobbyists grew up with, Crossocheilus siamensis, is now generally treated as a synonym of the earlier-described Crossocheilus oblongus[4], and "Crossocheilus siamensis" has separately been documented as a name misapplied, at various points, to more than one distinct species[2]. The Chinese algae eater's scientific name, Gyrinocheilus aymonieri, is more settled, but the common name "algae eater" applied generically in shops is exactly where the two get conflated — a label reading simply "algae eater" or even "Siamese algae eater" is not a reliable guarantee of which genus is actually in the tank.

Adult size

Both species are commonly sold small and grow considerably larger than their point-of-sale size suggests. The Siamese algae eater is commonly cited around 15cm (6in), with some sources reporting slightly larger under ideal conditions[3]. The Chinese algae eater is commonly cited at 10–15cm (4–6in), occasionally more[1]. The two overlap in raw length more than their reputations suggest — the meaningful difference is less about final size and more about temperament and tank footprint, covered next.

How temperament changes with maturity

This is where the two species genuinely part ways. The Siamese algae eater is generally described as a peaceful community fish throughout its life, gregarious as a juvenile and loosely shoaling as an adult, though specialist sources note it can become somewhat more boisterous or territorial toward its own kind in a smaller, more crowded tank[3].

The Chinese algae eater's temperament shift is more pronounced and better documented: adults are widely described as semi-aggressive and increasingly territorial with age, and the species is specifically reported as intolerant of its own kind[1]. As algae alone becomes nutritionally insufficient, a meaningful proportion of adults are reported to begin feeding on the body slime of slower, broad-sided tankmates — angelfish, discus and goldfish are the most frequently mentioned targets[1]. This isn't bad luck or a training failure; it's a documented, growth-linked pattern, covered in full in our Chinese algae eater guide.

Alone or with their own kind?

A Siamese algae eater tolerates its own species reasonably well, and a small group is sometimes recommended over a single individual, particularly in a larger tank[3]. A Chinese algae eater is a different case entirely: keeping two together is specifically flagged as inviting near-certain conflict, since the species is documented as intolerant of conspecifics regardless of tank size — a larger tank reduces but doesn't reliably eliminate this[1]. If you're planning to keep more than one algae-eating fish of the same kind, that plan only really works with the Siamese algae eater, not the Chinese one.

Tank size and footprint

Both need meaningfully more room than their juvenile sale size implies. Specialist retail sources commonly suggest a minimum of around 114 litres (30 US gallons) for a Siamese algae eater[3]. The Chinese algae eater generally needs more still — commonly cited at 150–280 litres (40–75 US gallons) for one adult kept long-term — reflecting both its larger adult size and the extra space that helps (without fully solving) its territorial behaviour[1]. Neither is a genuinely small-tank fish; see "Alternatives for a smaller tank" below if your setup doesn't reach either figure.

Flow, oxygen and temperature

Both species come from fast-flowing habitats and are reported to do best with moderate to strong water flow and good oxygenation, closer to the current-loving end of typical community-tank guidance than a gentle, slow-flow setup[1][3]. Temperature ranges are broadly similar and overlap comfortably — roughly 20–27°C (68–80°F) for the Siamese algae eater and roughly 22–27°C (72–81°F) for the Chinese algae eater — so temperature isn't the differentiating factor here; current and territorial space are. Our filter turnover calculator can help you check whether your filtration reaches the higher end of what either species is reported to prefer.

Do they keep eating algae as adults?

This is the single most consequential practical difference, and it's the reason getting the identification right matters beyond curiosity. The Siamese algae eater is widely reported as one of the few aquarium fish that will reliably eat black beard algae (BBA) throughout its life, a tough algae type many other grazers ignore[3]. The Chinese algae eater eats algae enthusiastically as a juvenile, but only partially as an adult — its nutritional needs shift toward more protein as it matures, and algae alone typically becomes insufficient[1]. Buying "an algae eater" without confirming which one you actually got can mean the fish you're relying on for long-term algae control stops doing that job by the time it's grown.

Neither species should be treated as a complete solution to an algae problem on its own — see our guide to algae in aquariums for the lighting and nutrient factors that matter alongside any grazing species, whichever one you choose.

Which suits a peaceful community tank?

This isn't a simple "one is good, one is bad" answer — both can be kept responsibly under the right conditions, and the Chinese algae eater isn't an inherently defective animal, just one whose needs and risks are less often explained at the point of sale. For most peaceful community setups, particularly ones that already include slow, broad-sided fish such as angelfish, discus or goldfish, a confirmed Siamese algae eater is the lower-risk choice: it stays smaller relative to its territorial behaviour, tolerates its own kind, and keeps grazing algae for life.

A Chinese algae eater can work well in narrower circumstances: a spacious tank at or beyond the upper end of its size guidance, stocked with fast-moving, robust fish rather than slow or broad-bodied ones, kept as the only individual of its species, and fed a protein-inclusive diet from a young age rather than left to rely on algae alone. Outside those conditions — a smaller community tank, or one with angelfish, discus or similar tankmates — it's a genuinely poor match regardless of how well it's otherwise cared for.

When a shop mislabels them

This isn't a rare, edge-case problem. Pet shops have been documented selling Chinese algae eaters as Siamese algae eaters to buyers who specifically asked for the calmer species, and the two are genuinely difficult to distinguish as small juveniles even for someone looking carefully[1]. If you suspect you've been sold the wrong one, the identification checklist above applies whether the fish is still in a shop's tank or already settled in yours.

If you've already got a Chinese algae eater you believed was a Siamese algae eater, the practical response is the same as if you'd bought it knowingly: check your other tankmates against the "slow, broad-sided fish" risk profile described above, start supplementing protein now rather than waiting for slime-feeding behaviour to appear, and reassess whether your tank size and stocking genuinely suit this species long-term. Rehoming to a more suitable setup, ideally as the sole individual of its kind in a larger, robust-fish community, is a reasonable option if your current tank doesn't fit that description and can't be adapted to.

Alternatives for a smaller tank

If your tank doesn't reach either species' minimum size guidance, neither is the right choice, and reaching for whichever one happens to be smaller as a juvenile just delays the same problem. Amano shrimp and Nerite snails are both effective, peaceful algae grazers without either species' size or territoriality requirements — see our Amano shrimp and Nerite snail guides, and our broader algae-eating fish and snails comparison for how these and other options stack up against each other.

Common mistakes

• Buying on the strength of a shop's "algae eater" or "Siamese algae eater" label alone, without checking the stripe, fins and mouth yourself.
• Assuming a Chinese algae eater will keep behaving like a juvenile Siamese algae eater once it matures, when the two diverge significantly.
• Keeping two Chinese algae eaters together, expecting the same tolerance a Siamese algae eater shows its own kind.
• Housing either species with a tank too small for its adult size, especially the Chinese algae eater's larger footprint requirement.
• Relying on either species as a complete fix for an existing algae problem without also addressing lighting and nutrients.

Frequently asked questions

How AquaPulse can help

AquaPulse can't identify which species is actually in your tank from a photo, and it won't tell you definitively that a fish is one species rather than the other — that's a physical identification question the checklist above is for, not something water-chemistry tracking can answer. Where it can help is once you've made a decision: keeping a record of which species you've confirmed and added, alongside your water testing, gives you a shared timeline to refer back to if you're later trying to work out whether a tankmate's condition is linked to a specific fish's behaviour.

Logging pH, temperature and core nitrogen-cycle readings in AquaPulse also matters more than usual here, since both species prefer stronger current and good oxygenation than a typical gentle community setup. Get AquaPulse on the App Store or Google Play to try it, or see the Water Check feature page for more detail.

Sources and editorial information

Good to know: This guide provides general informational guidance only. It doesn't replace physically checking a specific fish's features against the identification points above, and it is not a substitute for specialist aquatic advice.

• [1] AquaPulse — "Chinese algae eater care" Our own already-published, separately sourced guide. Used for Chinese algae eater identification, adult size, temperament, tank-size guidance, and the diet/slime-feeding shift — see that guide's own sources list for the underlying taxonomic, government and specialist references.
• [2] Seriously Fish — "Crossocheilus langei" Specialist aquarium-species reference source, already cited on our Siamese algae eater guide. Used here for the documented history of the "Crossocheilus siamensis" name being applied to more than one species.
• [3] AquaPulse — "Siamese algae eater care" Our own already-published, separately sourced guide. Used for Siamese algae eater identification, adult size, temperament, tank-size guidance and its black-beard-algae-eating reputation — see that guide's own sources list for the underlying taxonomic and specialist references.
• [4] FishBase — "Crossocheilus oblongus, Siamese flying fox" Specialist ichthyological reference database, already cited on our Siamese algae eater guide. Used here for the current valid scientific name and its synonymy with the historically used name Crossocheilus siamensis.

What we deliberately left out: a single ranked "better fish" verdict independent of tank conditions, since which species suits a given tank depends on its size, existing stock and the buyer's tolerance for territorial behaviour, not a fixed ranking; and a precise maximum size for either species, since both already-cited guides note genuine disagreement between specialist sources on the exact upper figure.

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