Otocinclus

Otocinclus are small armored catfish native to South America, found across a wide range of countries from Venezuela down through Argentina. Most specimens in the hobby are wild-caught, which matters more than people expect. They come from slow, warm, heavily vegetated streams where biofilm and algae grow thick on every surface.

In a tank they rarely exceed 4 cm and have a neat striped pattern running from snout to tail, which varies a bit between the several species sold under the same common name. They're genuinely peaceful and spend most of their time methodically grazing on glass, leaves, driftwood, and hardscape. Diatoms are their specialty, and a new tank going through a brown algae phase will look spotless within days if you've got a group working it over. Soft green algae is also on the menu, but don't expect them to touch hair algae or cyanobacteria.

Water quality is where most people struggle. Otos are notoriously sensitive and don't handle ammonia or nitrite at all. Soft, slightly acidic water replicating their natural habitat suits them best, but they'll tolerate neutral pH fine. Temperature-wise, they're comfortable in the cooler end of tropical ranges and actually do better if you don't push the heat too high.

You'll need to supplement their diet with zucchini, blanched spinach, or algae wafers, especially in a clean tank where natural food runs low. A group that's getting enough food will be noticeably active and chunky-bellied. Thin, lethargic otos are usually starving. Browse real community setups featuring these guys to see how other hobbyists keep them well-fed and thriving alongside plants.