Common Otocinclus

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.

Water: Maintain soft to moderately hard water (GH 2–12, KH 1–8) at pH 6.0–7.5 and temperature 20–26°C; pristine quality is essential — zero tolerance for ammonia or nitrite and nitrates below 20 ppm. Tank: A minimum 40-litre aquarium with dense planting, smooth stones, and driftwood provides grazing surfaces and security; gentle flow from a sponge filter is ideal. Feeding: Supplement natural biofilm with blanched courgette, cucumber, spinach, and high-quality algae wafers; newly imported fish are fragile and may refuse prepared foods initially. Breeding: Egg scatterers that deposit adhesive eggs on plant leaves; soft, slightly acidic water and conditioning with live foods encourages spawning; fry require fine green algae or infusoria. Compatibility: Excellent with all small peaceful fish, shrimp, and snails; avoid large, predatory, or aggressive species; ideal companions include small tetras, rasboras, and dwarf cichlids.