Otocinclus

Otocinclus — "otos" to most aquarium keepers — are among the smallest of the suckermouth catfishes. They spend the day stuck to leaves, stones and glass, grazing a thin film of algae, which has made them the favourite clean-up crew of people with planted tanks.

A genus, not a single fish

Otocinclus is a genus of around twenty species, spread over much of tropical and subtropical South America. They look much alike: small, slim, with a brownish or olive back, a pale belly and a dark stripe along the side. The ones sold most often are O. vittatus, O. affinis and O. macrospilus, and shops frequently mix them up. A few look clearly different, such as the striped zebra oto (O. cocama) from Peru. In the wild, otos live in shoals in shallow, slow, well-planted waters, often among the roots and leaves along the banks.

Built for grazing

Like their larger relatives, the plecos, otos have a mouth shaped like a suction cup, lined with small teeth that scrape algae and the film of microbes that grows on every surface under water. Their bodies are covered in bony plates instead of ordinary scales. They also have an unusual trick: they can gulp air at the surface and take oxygen from it through their gut, which helps them in warm, still water.

Keeping otos

Otos are not hard to keep, but they are hard to keep alive at first. Most are still caught in the wild, and many arrive starved and stressed after the journey. They do best in a mature, planted tank that already has algae and biofilm to graze, with clean, stable water and gentle tank mates. Feed them extra — algae wafers, blanched courgette or spinach — since a single tank rarely grows enough algae for a group. They are social and timid on their own, so keep six or more. They rarely breed in home aquariums, though it does happen: the eggs are laid one by one on leaves and glass.