Siamese Algae Eater (Crossocheilus oblongus)

The Siamese Algae Eater (Crossocheilus oblongus), also commonly sold as Crossocheilus siamensis, is one of the most sought-after algae-eating fish in the planted aquarium hobby. Native to rivers and streams of Thailand and Malaysia, it is notable for its willingness to consume black beard algae (Audouinella/Compsopogon species) — one of the most persistent and difficult algae problems in planted tanks — which very few other fish will eat.

It features a streamlined silver body with a distinctive brown-black stripe running from the tip of the snout to the base of the caudal fin. The stripe extends into the tail fin (unlike similar species such as the Flying Fox and False Siamese Algae Eater, where the stripe stops at the caudal peduncle), which helps with correct identification.

Siamese Algae Eaters are active, fast-moving fish that spend significant time grazing on plant surfaces, rocks, driftwood, and substrate. They grow to about 12–14 cm and are peaceful toward other species, though adults may become territorial with their own kind. Juveniles under 5 cm are the most efficient algae eaters; adults tend to eat more prepared food.

They are hardy and adaptable to a range of water conditions. Good water quality, moderate lighting, and a varied diet including algae are important for their long-term health in the planted aquarium.

Water Parameters: pH 6.5–7.5, temperature 24–28°C, GH 5–20. Adaptable and hardy. Good filtration and moderate water flow are appreciated. Stable water parameters support long-term health. Weekly water changes of 25–30%.

Tank Setup: Minimum 100 liters. They are active, fast-moving fish that need open swimming space alongside planted areas. Provide driftwood and flat rocks for resting and grazing. Strong filtration is beneficial. A tight-fitting lid is important as they can jump when startled.

Feeding: Primary algae grazers but will eat sinking pellets, algae wafers, flake food, and frozen foods as they mature. Feed algae wafers, blanched vegetables, and spirulina flakes. Do not overfeed prepared foods or they will ignore algae. Rotate diet to ensure adequate algae grazing.

Tankmates: Peaceful toward other species. May show territorial behavior toward other Siamese Algae Eaters in small tanks — either keep singly or in larger groups (3+) in spacious aquariums to distribute aggression. Compatible with most peaceful community fish.

Health: Robust and generally disease-resistant. Ensure good water quality and varied diet for longevity. Avoid overcrowding. Adults can live 8–10 years with proper care.