Siamese Algae Eater Care Guide - Aquarium Setup, Diet & Breeding

The Siamese Algae Eater is a slender, energetic freshwater fish with a silver to grey body and a strong black stripe running from the snout through the eye and along the side to the tail. The stripe is usually sharply defined, while the fins are mostly transparent and the body has a streamlined shape suited to life in running water.

Crossocheilus oblongus is an active bottom and midwater swimmer that spends much of its time exploring surfaces, grazing and searching for edible scraps. Younger fish are especially valued by aquarists for their willingness to consume certain types of filamentous algae, although their appetite and habits change as they mature.

In the wild, these fish are associated with clear, oxygen-rich streams and rivers with gravel, sand, submerged wood and stones. Their underslung mouth and scraping lips help them feed from solid surfaces, while their powerful swimming style allows them to hold position in current.

Siamese Algae Eaters are generally peaceful community fish, but adults can become assertive with one another, particularly when kept in cramped conditions. They are often confused with the Flying Fox and Chinese Algae Eater; the continuous dark stripe and transparent fins help distinguish the true Siamese Algae Eater from these lookalikes.

Siamese Algae Eaters are native to mainland Southeast Asia, including parts of Thailand, Cambodia, Laos and the Malay Peninsula. They inhabit flowing rivers and streams connected with the Mekong, Chao Phraya and nearby drainage systems.

A group of Siamese Algae Eaters should have at least 100 litres, with a tank measuring around 120 cm long by 40 cm wide providing a better adult footprint. Use a fine sand or smooth gravel substrate, strong filtration and good oxygenation, with open swimming space alongside rounded stones, driftwood and robust plants for grazing. Moderate water movement, shaded areas and a secure lid are beneficial, as these active fish may jump when startled.

Up to 15 cm (6 in) in total length. Females are usually slightly larger and noticeably deeper-bodied than males, while males tend to remain slimmer.

Offer a varied omnivorous diet built around algae wafers, sinking foods and vegetable matter, supplemented with blanched courgette, spinach, cucumber or shelled peas. They also eat biofilm, soft algae and small aquatic invertebrates, and will accept quality flakes or pellets. Do not rely on natural algae alone, particularly in a mature aquarium where their demand may exceed the available food.

Siamese Algae Eaters suit peaceful community aquariums containing fish such as rasboras, danios, tetras, peaceful barbs, gouramis, dwarf cichlids and other non-aggressive bottom dwellers. Avoid housing them with large predatory or highly aggressive species, and take care when combining them with territorial bottom fish or similarly shaped algae grazers. They should not be confused with the more aggressive Chinese Algae Eater, which is a poor substitute for a peaceful community setup.

Siamese Algae Eaters are egg-scattering spawners, but successful aquarium breeding is uncommon. In nature, adults migrate and spawn in flowing water, while captive production generally relies on commercial hormone treatments. A mature group may occasionally spawn after changes in water flow and conditions, but the eggs and fry require specialised care and are rarely raised in ordinary community aquariums.

Females are generally fuller through the abdomen and slightly larger when mature. Males are more slender, with less body depth; outside of this difference, the sexes are difficult to distinguish reliably.