Siamese Algae Eater

The Siamese algae eater (Crossocheilus siamensis) is a slender freshwater fish in the carp family Cyprinidae, native to fast-flowing rivers and streams of mainland Southeast Asia, including Thailand, Malaysia, and parts of Indonesia. It is frequently confused in the aquarium trade with several similar-looking relatives, most notably the flying fox (Epalzeorhynchos kalopterus), leading to widespread mislabeling. True Siamese algae eaters are valued for actively grazing on a wider variety of algae types than most other algae-eating aquarium fish. The species belongs to a broader group of small Southeast Asian cyprinids adapted to fast-flowing, well-oxygenated stream habitats.

Siamese algae eaters are identified by their slim body and bold lateral stripe.

• Slender, torpedo-shaped body, silvery-tan to olive above, paler below
• A single, well-defined dark horizontal stripe running from the snout through the eye to the base of the tail
• Small barbels at the corners of the mouth
• Clear to faintly yellow-tinged fins, without dark markings
• Grows to 10-16 cm

Distinguished from the commonly confused flying fox by its clear, unmarked fins and less pronounced barbels, and from false 'siamensis' relatives by a straighter, more consistent stripe that does not zigzag or fade toward the tail.

Siamese algae eaters inhabit moderately to fast-flowing freshwater rivers and streams across mainland Southeast Asia, particularly in Thailand's Chao Phraya and Mekong basins. They favor clear, well-oxygenated water over rocky, gravel, or sandy substrates with exposed surfaces for grazing algae, generally in water temperatures around 24-28C. They are often found in areas with moderate current and some vegetation or submerged wood offering cover. Populations can also occupy calmer tributary streams and flooded seasonal habitats during wetter months, though they generally prefer more oxygenated, flowing water than many other small Southeast Asian cyprinids.

Siamese algae eaters are active, mid-to-bottom dwelling fish that spend much of the day grazing algae and biofilm off rocks, wood, and plant surfaces, using a specialized mouth structure to rasp food from hard surfaces. They are generally peaceful and can be loosely social, sometimes forming small groups, though individuals may show mild territoriality over favored grazing spots as they mature. They are most active during daylight hours, becoming still at night. Beyond algae, they will also take small invertebrates and organic debris opportunistically. Wild reproductive behavior is not well documented, though spawning is believed to be associated with seasonal high-flow periods in their native rivers.