Chinese Algae Eater

The Chinese algae eater (Gyrinocheilus aymonieri) is a freshwater fish native to fast-flowing rivers and streams of mainland Southeast Asia, including Thailand, Laos, Cambodia, and Vietnam, and the sole widely kept representative of the family Gyrinocheilidae. Despite the common name, it is not native to China. Its most distinctive feature is a modified sucker-mouth adapted for both feeding on algae and for respiration, allowing water to pass over the gills while the mouth remains attached to a surface. Chinese algae eaters are widely sold in the aquarium trade while young for algae control, though they can grow considerably larger and more territorial as adults than many keepers anticipate.

The Chinese algae eater is identified by its elongated shape and unusual sucker-mouth.

• Slender, torpedo-shaped body, olive-brown to golden-tan
• A dark horizontal stripe or line of connected blotches runs along the midline in younger fish, often fading in adults
• Large, round, ventral sucker-disc mouth ringed with fine rasping structures
• Single dorsal fin set forward on the body; forked tail fin
• No barbels, unlike many superficially similar bottom-dwelling loaches
• Grows to 15-28 cm

Its modified sucker mouth, used both for feeding and respiration, along with the absence of barbels, distinguishes it from true loaches and other algae-grazing catfish.

Chinese algae eaters are native to fast-flowing, well-oxygenated rivers and streams across mainland Southeast Asia, including the Mekong and Chao Phraya basins. They favor rocky or gravel substrates in areas with moderate to strong current, where algae growth is abundant on submerged surfaces. Preferred water temperatures range roughly from 22-28C. Juveniles are often found in shallower, calmer margins, while adults move into faster, more open sections of river. Outside their native range, released aquarium specimens have established populations in some warm freshwater systems, where they can compete with native algae-grazing species for food and habitat.

Chinese algae eaters spend much of their time attached to rocks and submerged surfaces by their sucker-mouth, rasping algae and biofilm while also using the mouth attachment to help maintain position in strong current. Juveniles are relatively peaceful and often found loosely grouped, but individuals become increasingly solitary and territorial with age, aggressively defending favored grazing areas from other fish, including their own species. They are most active during the day, resting motionless attached to surfaces at night. As algae supplies dwindle with maturity, adults shift toward a broader diet including small invertebrates and organic debris. Wild spawning behavior is not well documented but is thought to occur during warmer, high-flow periods.