Taxonomy & naming
Gyrinocheilus pustulosus was described by the French ichthyologist Léon Vaillant in 1902. It belongs to the family Gyrinocheilidae — a small, ancient lineage with a single genus, Gyrinocheilus, and only three recognised species: G. aymonieri, G. pennocki, and G. pustulosus. The family has no close relatives among the mainstream loach families (Cobitidae, Botiidae, Nemacheilidae) and occupies its own position within the broader superfamily Cobitoidea.
In the aquarium trade, all three Gyrinocheilus species are sold interchangeably as "Chinese algae eater" or "Siamese algae eater," with little commercial effort to distinguish them. G. aymonieri is by far the most commonly traded species, but G. pustulosus and G. pennocki enter the trade from the same range and are regularly misidentified at point of sale. The golden or albino colour form sold as "golden algae eater" is a selectively bred or leucistic variant of G. aymonieri but is sometimes mislabelled as other species.
The Catalog of Fishes (Eschmeyer, California Academy of Sciences) lists Gyrinocheilus pustulosus as the valid combination. No major synonyms are recorded.
Morphology
Gyrinocheilus pustulosus is a robust, cylindrical loach with a slightly depressed underside and an arched dorsal profile. Adults reach approximately 10–11 in in total length — substantially larger than the juvenile fish sold in the trade. The body is covered in small, embedded scales that give the skin a smooth, near-scaleless feel, and the coloration is typically a warm brown or olive-gold with a lateral dark stripe or mottled patterning across the flanks, though this varies with light and mood.
The most anatomically distinctive feature is the sucker-like mouth: fleshy, ventrally positioned lips form a disc adapted for clamping to rock surfaces and rasping algae and biofilm in fast current. Crucially, the gills have separate inhalant and exhalant openings — unique among freshwater fishes — allowing the fish to breathe through a divided gill cover while its mouth remains clamped to a substrate. This adaptation is what makes Gyrinocheilus a genuine specialist for high-current environments, not merely a sucker-mouthed generalist.
Unlike the botiid loaches, Gyrinocheilus does not carry an erectile suborbital spine. The pectoral and pelvic fins are well developed for anchoring in flow.
Habitat
Gyrinocheilus pustulosus is native to the river systems of Southeast Asia, including the Mekong and Chao Phraya drainages across Thailand, Laos, Cambodia, and Vietnam. It inhabits fast-flowing, highly oxygenated rivers and hill streams where the current is strong enough to keep substrate surfaces clean and biofilm productive. The typical environment is rocky or gravelly, with well-lit patches promoting aufwuchs growth and water that remains clear and well-oxygenated even in warmer months.
Water conditions across its range are warm (approximately 72–79 °F), close to neutral to slightly acidic (pH 6.5–7.5), and frequently of moderate hardness. This is fundamentally a river fish of turbulent, oxygen-rich water — not a pond, swamp, or still-water species. In aquarium terms it requires strong flow and high dissolved oxygen; still, warm, oxygen-depleted setups are unsuitable and will slowly compromise the fish's health and behaviour.
Feeding
Juvenile Gyrinocheilus pustulosus are genuinely effective aufwuchs grazers. The sucker mouth scrapes algae, diatoms, biofilm and small invertebrates from hard surfaces, and young fish kept in well-lit, mature tanks with an established algae layer will work methodically across glass, slate, and wood. This is the feeding behaviour the trade name sells, and for juveniles under about 4–4.5 in it is broadly accurate.
As the fish grows, the diet shifts. Larger Gyrinocheilus require more protein — sinking pellets, sinking wafers, blanched vegetables, and occasional meaty foods such as bloodworm. More seriously, adult fish may begin to rasp the slime coat of slow-moving, flat-bodied tankmates: corydoras, plecos, discus, angelfish, and other fish that hover or rest are at risk. This behaviour is not aberrant; it is a predictable expression of the opportunistic omnivory the adult fish is built for. The algae-eating role that justified buying the fish diminishes; the aggression-and-injury risk to other fish grows. Any keeper who buys a Gyrinocheilus for algae control should understand they are acquiring a fish that will, in time, largely abandon that role.
Mating
Sexual dimorphism in Gyrinocheilus pustulosus is not reliably documented. As with the congener G. aymonieri, ripe females are likely plumper in the belly region, and subtle differences in overall body depth may develop with maturity, but no consistent external character distinguishes the sexes with certainty in aquarium fish.
In the wild, spawning in Gyrinocheilus is believed to be tied to seasonal rainfall and river-level fluctuations, as is typical for riverine fishes of the Mekong and Chao Phraya drainages. Ripe fish are thought to scatter eggs over gravel or rocky substrate in flowing water; no elaborate courtship or pair-bonding behaviour has been documented. The full details of wild reproductive behaviour for G. pustulosus specifically remain poorly described in the scientific literature.
Breeding
Gyrinocheilus pustulosus is not bred in home aquaria. It is an egg-scatterer with no parental care — eggs are released into the water column or over substrate in fast-flowing river conditions, and neither parent guards or attends the spawn. The combination of large adult size, uncertain sexing, likely seasonal hydrological triggers, and the need for strong riverine flow makes home spawning essentially unrealisable with ordinary aquarium infrastructure.
The fish sold in the trade are produced commercially on Southeast Asian farms via hormone induction: brood fish are injected to bring them into spawning condition, stripped or allowed to spawn under farm conditions, and the resulting fry are reared in ponds. This is the honest breeding picture for all Gyrinocheilus in the trade. A keeper should not expect to breed this fish and should buy it with no breeding intentions — the commercial supply is fully farm-based and does not depend on or expect hobbyist reproduction.
In the aquarium
Gyrinocheilus pustulosus is a fish whose care requirements and eventual behaviour are systematically misrepresented at the point of sale, and understanding both honestly is the starting point for keeping it well. A juvenile of 2–3 in is a useful, peaceful community fish that earns its place by grazing algae. An adult of 10–11 in is a large, territorial bottom-dweller that may injure or kill tankmates it once ignored. The keeper who buys the juvenile must be prepared for the adult.
The minimum practical tank for an adult is in the range of 55–80 US gal, with strong filtration producing good flow and high dissolved oxygen — this is a river fish that breathes through gill openings adapted for fast water. Substrate should be smooth gravel or rounded stone; sharp sand can abrade the ventral surface. The tank must have well-established hard surfaces with biofilm and algae for grazing, supplemented with regular offerings of sinking pellets, wafers and blanched vegetables. Meaty foods help once the fish is large.
Because adult Gyrinocheilus become aggressive toward other bottom-dwellers and toward any slow fish large enough to rasp, tankmate selection becomes increasingly restricted with age. Flat-bodied or sedentary fish — corydoras, plecos, discus, angelfish — are at risk from slime-coat rasping once the fish is sub-adult. Robust, active mid-water fish of similar or larger size fare better. Keeping more than one Gyrinocheilus together is generally not recommended; adults are highly intolerant of conspecifics. Unlike most loach groups, Gyrinocheilus is not a social or schooling fish and does not need companions of its own kind.
Conservation
Gyrinocheilus pustulosus has not been formally assessed on the IUCN Red List and carries the status Not Evaluated (NE). No targeted population assessments for this species specifically have been published, and its distribution and abundance across the Mekong and Chao Phraya drainages are not formally documented in conservation literature.
The broader Gyrinocheilus genus, and Southeast Asian river fish generally, face persistent habitat pressures: dam construction on the Mekong and its tributaries, sedimentation from land-use change, agricultural runoff, and the alteration of natural flood-pulse regimes all affect the riverine habitats these fish depend on. The commercial trade in Gyrinocheilus is supplied by hormone-induced farm production, which in principle reduces direct pressure on wild populations; the scale of any continued wild collection for the ornamental trade is not well documented. Until a formal assessment is conducted, no conservation status can honestly be assigned.