Otocinclus affinis is the most frequently encountered member of a diverse genus of miniature loricariid catfishes native to South America. Commonly known as the dwarf suckermouth or Otto cat, this small species rarely exceeds 4 cm and is instantly recognisable by its torpedo-shaped body, armoured scutes, and prominent ventral sucking disc used to rasp algae and biofilm from hard surfaces.
In the wild, O. affinis inhabits shallow, clear to slightly turbid streams and river margins across a broad range of Brazil, where it forages in schools over algae-coated rocks, plant leaves, and submerged wood. It is a strictly herbivorous grazer, subsisting almost entirely on periphyton — the complex community of algae, bacteria, and organic matter that colonises submerged surfaces. This dietary specialisation means it is uniquely effective at controlling soft green algae in the planted aquarium without disturbing plants or other inhabitants.
In the aquarium, Common Otocinclus are peaceful, active, and highly social. They must be kept in groups of at least six, as solitary individuals often waste away from stress. They are sensitive to poor water quality and do not adapt easily from wild conditions, making acclimatisation critical. Once established, however, they are hardy and long-lived, patrolling every surface of the aquarium in constant search of algae and biofilm.
