Otocinclus

Looks how to spot one

Armoured catfish (bony plates)

A tiny, slim catfish clad in rows of bony armour plates instead of ordinary scales, with a sucker-shaped mouth on the underside of the head for clinging to leaves and glass while it grazes. Across the genus adults range from about 2.4 cm to 5.5 cm; the species usually sold measure roughly 3.3-3.5 cm. A dark stripe along the side is typical, and some species, such as O. macrospilus, carry a round black spot at the base of the tail. Seen from above, females look a little broader than males.13546

Personality what they are like

A very peaceful, rather shy little fish that spends its day stuck to leaves and surfaces, quietly grazing. It feels secure only in a group of its own kind and in a well-planted tank, and it gets along with small, calm tankmates such as little tetras and dwarf cichlids.42

Daily activity how busy a day looks

Steadily active during the day, moving from leaf to leaf and across glass and wood as it grazes. It likes clean, well-oxygenated water with a gentle to moderate flow; it will also dart to the surface now and then to take a gulp of air.14

Grooming and care the hands-on bits

Best added to a mature, well-established planted tank where natural algae and biofilm are already growing, with stable water and regular partial water changes. Typical water: about 20-26 C, pH roughly 5.5-7.5, hardness about 1-18 dGH depending on species. Newly imported fish are often thin after transport, so feed them generously while they settle.432

Home where they are happiest

A tank with a footprint of at least 45 x 30 cm (around 40 litres) for a small group, heavily planted with broad-leaved plants, driftwood and a soft sand bottom. Clean, oxygen-rich water with some movement suits its stream-side origins.41

Food basics what goes in the bowl

Mainly a herbivore that rasps algae and the thin film of microlife off plants, stones and wood. Natural growth in the tank should be backed up with algae wafers and blanched vegetables such as courgette, cucumber or spinach; small frozen foods like bloodworm or daphnia can be offered now and then.142

Company who they like around

A schooling fish that should live in a group of at least six; kept alone or in tiny numbers it becomes stressed. Choose calm companions that will not outcompete it at feeding time.421

The story where it all began

The American naturalist Edward Drinker Cope named the genus in 1871, and further species followed through the 20th and 21st centuries, among them O. vittatus (Regan, 1904) and O. macrospilus (Eigenmann & Allen, 1942); about 21 are recognised today. The fish belong to a large group of small South American suckermouth catfishes, the Hypoptopomatinae, whose classification has been revised several times as genetic studies have reshaped the family tree. Otos became popular in the aquarium hobby as living algae cleaners for planted tanks. Because breeding them in captivity is difficult, the trade relies mostly on wild-collected fish, and species are often mixed up and sold under the wrong name.12576

Recognised by the official bits

Taxonomy

Genus Otocinclus Cope, 1871, about 21 valid species; armoured suckermouth catfishes of the family Loricariidae, subfamily Hypoptopomatinae1

IUCN Red List

O. vittatus: Least Concern (assessed 21 October 2020)3

IUCN Red List

O. macrospilus: Least Concern (assessed 23 April 2014)5

Trade naming

Fish sold as O. affinis are usually other species (O. vittatus, O. vestitus, O. macrospilus or O. huaorani); the true O. affinis from south-eastern Brazil is rare in the hobby6