All fish / Loricariidae

Arnold's Otocinclus

Otocinclus arnoldi

Also known as otocinclus, oto, dwarf sucker, oto cat, arnoldi oto, golden oto, otocinclus catfish, dwarf suckermouth catfish, オトシンクルス・アーノルディ, オトシン, 小精灵, 阿诺德耳斑鲶

A small suckermouth catfish with a pale belly, a brownish back with mottling, and a dark stripe running along its side to the tail. Keepers like it as a gentle, sociable grazer that cleans soft algae and biofilm off plants and glass in planted community tanks.

Care at a glance

Care level

Moderate

Temperament

Peaceful

Adult size

4 cm

Temperature

18 to 25 °C

pH

6 to 7.5

Smallest tank

60 litres

Keep as

Group of 6 or more

Diet

Herbivore: biofilm and soft algae, plus algae wafers, blanched courgette and spinach, and the odd small frozen food

Swims

Bottom of the tank

Lifespan

3 to 5 years

Water

Freshwater

Wild range

Lower Paraná and Uruguay river basins and coastal drainages of southern Brazil, Uruguay and Argentina

Breeding

It spawns in planted tanks, with females sticking single eggs to leaves and glass after courtship that resembles Corydoras behaviour. Breeding happens now and then in well-fed groups kept in mature tanks, but raising the tiny fry is difficult because they need plenty of fine algae and biofilm.

Good to know

Wild-caught fish often arrive underfed and are prone to losses in their first weeks, so pick plump specimens and only add them to mature tanks that have algae growing. It suits slightly cooler water than most otos and is often sold mixed with similar Otocinclus species.