Otocinclus Catfish Care Guide - Aquarium Setup, Diet & Breeding

Otocinclus Catfish are small, delicately built loricariid catfish with a flattened body, underslung sucker mouth and a dark lateral stripe running from the snout towards the tail. Their mottled brown, grey and golden colouring helps them disappear against leaves, wood and the dappled surfaces of their natural streams.

These peaceful fish spend much of their time clinging to glass, plant leaves, rocks and driftwood while grazing. They are active without being disruptive, and their gentle nature makes them a popular choice for calm community aquariums.

In the wild, Otocinclus affinis inhabits shallow, flowing waters where sunlight encourages the growth of algae and microorganisms. It uses its sucker-like mouth to scrape food from submerged surfaces, while its flattened shape helps it remain attached in moving water.

Otocinclus Catfish are social and usually appear more confident when kept in a group. Although often described simply as algae eaters, they are specialised grazers with delicate feeding requirements, and their long-term success depends on access to varied natural and prepared foods.

Otocinclus affinis is native to southeastern Brazil in South America, where it occurs in clear, shallow streams and river margins with abundant vegetation, algae and biofilm. The name is also widely used in the aquarium trade for several closely related Otocinclus species.

A group of Otocinclus Catfish should be kept in an established aquarium of at least 40 litres, with a practical footprint of around 60 × 30 cm or larger. Use gentle to moderate circulation, excellent oxygenation and stable, clean water. Provide live plants, driftwood, smooth stones and broad leaves for grazing, along with shaded areas and hiding places. A soft sand or fine, smooth-grained substrate is ideal and helps prevent damage to their sensitive underside and mouth.

Up to about 5 cm (2 in) in total length. Females are generally broader-bodied and slightly larger than males, which usually reach around 3.5–4.5 cm (1.4–1.8 in).

Their natural diet consists mainly of soft algae, aufwuchs and biofilm gathered from plant surfaces, wood and rocks. Offer a varied supplement of algae wafers, sinking herbivore foods and blanched vegetables such as courgette, cucumber, spinach or kale. They may also accept Repashy-style foods and other soft foods, but should not be expected to survive on naturally occurring aquarium algae alone.

Otocinclus Catfish are peaceful community fish and suit small tetras, rasboras, danios, peaceful livebearers, small gouramis and other non-aggressive species. They can also be kept with calm shrimp and compatible snails. Avoid large, boisterous or predatory fish, fin-nippers and aggressive cichlids, as Otocinclus are easily outcompeted, stressed or injured.

Otocinclus Catfish are egg scatterers that may spawn naturally in a mature, well-planted aquarium. A conditioned group can be encouraged with excellent water quality, plentiful vegetable foods and a slight change to cooler, softer, well-oxygenated water. Females scatter small adhesive eggs among plants, on leaves or on aquarium surfaces, and the adults should be separated if a significant number of fry are desired. The tiny young need infusoria, algae and other microscopic foods before progressing to powdered or finely crushed foods.

Females are typically larger and noticeably wider through the abdomen when viewed from above. Males are usually smaller and slimmer, although sexing young Otocinclus Catfish can be difficult.