Siamese Algae Eater: The One Fish That Actually Eats the Worst Algae

In this guide

Overview

The true Siamese algae eater, Crossocheilus oblongus, holds a genuinely unique position in the aquarium hobby: it is one of the very few fish that reliably eats black beard algae, a stubborn, difficult red algae that most other algae eaters simply ignore. It comes from Southeast Asia and can reach up to fifteen centimetres, though most aquarium specimens stay smaller.

Complicating matters, the true Siamese algae eater is one of the most commonly mislabelled fish in the trade. It is routinely confused with, and sold as, the flying fox, which looks similar as a juvenile but is more territorial, less effective at eating algae, and a poorer choice for serious algae control.

Telling it apart and tank requirements

A true Siamese algae eater has a clean, straight black stripe running from nose to the very tip of the tail with no red or yellow fin colouration, while a flying fox shows a stripe that stops before the tail and often carries reddish or yellow tinges on the fins. A group of five or six does well in a tank of eighty litres or more, with a secure lid, since this species is a notable jumper.

It is hardy and tolerant of a wide range of water conditions, including typical Indian tap water, and does not require particularly soft or acidic water to thrive.

Diet and behaviour

Algae, particularly black beard algae, forms a valuable part of its diet, supplemented with algae wafers and blanched vegetables once established. Unlike the more solitary, aggressive flying fox, the true Siamese algae eater is genuinely peaceful and can be kept in a small group.

It mixes well with most calm community fish and rarely causes any trouble beyond an occasional nibble at plants if underfed.

Buying tips

• Priced around sixty to one hundred fifty rupees per fish, with true stock sometimes commanding a premium from specialist shops that can guarantee the species
• Check the tail stripe carefully before buying, since flying fox is routinely sold under the Siamese algae eater name
• A worthwhile investment specifically for a planted tank struggling with black beard algae, which almost nothing else in the hobby reliably eats

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