The Otocinclus, or oto, is a small suckermouth catfish from South America and one of the better genuine algae-grazers for the planted community tank.
It works over leaves and glass, removing soft algae and biofilm too delicate for larger plecos.
Its intermediate rating is well earned: most otos die not because they are hard to keep but because they are sold half-starved, often wild-caught, and rushed into immature tanks before there is enough biofilm to sustain them.
Housing
Keep a shoal in a well-established, fully cycled tank of at least 75 litres (20 gallons) with a stable, mature growth of algae.
Maintain 22-27C (72-81F), pH 6.0-7.5, and clean, well-oxygenated water with low nitrate.
Never add otos to a brand-new tank; they need an aged setup with soft green algae already growing.
Provide plants, driftwood, and gentle flow.
They are highly sensitive to ammonia and nitrite, so the cycle must be solid before they arrive.
Diet
Otocinclus are dedicated herbivores that graze soft green algae and biofilm.
In tanks with insufficient algae they will starve, so always supplement with blanched vegetables such as courgette, cucumber, and spinach, plus quality algae wafers.
Many new otos arrive emaciated and need immediate, reliable feeding to recover; a sunken belly is a danger sign.
Keep a steady supply of grazing food and vegetables.
They cannot subsist on commercial flake intended for other fish.
Health
The biggest killer of otos is starvation, both before purchase and in algae-poor tanks.
Combined with their sensitivity to poor water and shipping stress, this makes the first few weeks critical.
Choose round-bellied, active individuals and acclimatise them slowly.
They tolerate medications, salt, and copper poorly, so treat with care.
Check belly shape daily: flat or sunken means underfeeding.
In a mature, stable, algae-rich tank with clean water they settle well and live several years.
Temperament
Otocinclus are peaceful, gentle shoaling fish that feel secure and graze openly only in groups of six or more.
Singly or in small numbers they hide and stress, so a true shoal is essential for natural behaviour.
They are harmless to tankmates and well suited to nano and planted communities alongside small tetras, rasboras, shrimp, and corydoras.
Keep them away from boisterous or large fish, which intimidate these small grazers.
Intermediate
Intermediate
Intermediate
Intermediate
Intermediate
Intermediate