Otocinclus Care Guide
The otocinclus, or "oto," is one of the most effective and peaceful algae eaters in the hobby. These tiny catfish spend their days grazing soft green and brown algae off glass, plants, and decor, making them a favorite for planted and nano aquariums. They are gentle, plant-safe, and small enough for setups where a pleco would be far too big. You can find them in our freshwater fish collection, including the standard Otocinclus and the unusual dwarf Nannoptopoma otocinclus. One important note up front: otos are sensitive fish that need an established tank, so they are not a good first-week addition.
Meet the Otocinclus
Otocinclus (Otocinclus spp.) are small suckermouth catfish from South America, reaching only about 1.5 to 2 inches. They are true algae specialists, peaceful to the point of being shy, and best kept in groups. Unlike many plecos, they will not damage live plants and will not outgrow a small tank. Their biggest challenge is that they often arrive at stores underfed after a long supply chain, which is why buying healthy, well-acclimated stock and feeding them properly from day one matters so much.
Tank Size and Setup
A group of six or more otos does well in a 20 gallon tank, though a mature 10 gallon can work for a small group. Crucially, the tank should be established and growing some algae before otos arrive, so they have a natural food source. A rimless nano aquarium or any tank from our glass aquariums collection works well. They thrive in a planted tank, so add plenty of live plants and some easy low-light plants that build up the biofilm and algae otos graze on. A gentle filter keeps water clean while leaving surfaces for grazing. For setup help, see our planted aquarium beginners guide.
Water Parameters and the Cycled Tank
Otos are sensitive to poor water quality, so stability is everything. Aim for a temperature of 72 to 79°F, a pH of 6.5 to 7.5, and soft to moderately hard water. Most importantly, never add otos to an uncycled tank: ammonia and nitrite spikes are often fatal to them. Read our nitrogen cycle guide and make sure your tank is fully cycled and mature first. Treat tap water with a quality dechlorinator, keep a test kit on hand, and use an adjustable heater for stable temperatures. Consistent weekly water changes and basic tank maintenance keep otos thriving.
Feeding: Algae Alone Is Not Enough
This is the most important part of oto care. Otos eat soft green and brown algae and biofilm, but a clean, well-maintained tank rarely grows enough to sustain a group long-term. You must supplement. Offer blanched vegetables like zucchini, cucumber, and spinach, plus algae wafers made for bottom feeders. A varied diet from our fish food collection, including the occasional frozen treat, keeps them in good condition. A healthy oto has a gently rounded belly; a sunken, pinched belly is a warning sign of starvation. For more options, see our best algae eaters guide and algae types guide.
Tankmates
Otocinclus are about as peaceful as fish get and make superb community members. They pair beautifully with dwarf shrimp (they will not bother shrimp or fry), corydoras, small tetras, and other gentle nano fish, plus snails for extra cleanup. Avoid large, aggressive, or fast fish that will outcompete them for food or stress them. Because they are shy, otos feel safest in a group and in a tank with plenty of plant cover. Browse compatible companions in our shrimp collection and beginner fish collection.
Schooling, Behavior, and Health
Otos are social and should be kept in groups of at least six; in larger numbers they are more active and graze out in the open during the day. The most common cause of oto loss is starvation in the first few weeks, so watch bellies closely and supplement feeding generously. The second is being added to an immature or unstable tank. Get those two things right and otos are long-lived, hardy little workers. Breeding in the home aquarium is uncommon but does happen in well-fed, planted tanks. For broader stocking ideas, see our guide to the best fish for beginner aquariums.
Is an Otocinclus Right for You?
Otos are ideal if you have an established, planted tank and want a peaceful, plant-safe algae eater that stays small. They are not the right choice for a brand-new tank or for someone who will not supplement their diet. If your tank is still cycling, hold off and start with hardier beginner fish first, then add a group of otos once the tank has matured.
Frequently Asked Questions
Can I add otocinclus to a new tank? No. Otos need a mature, fully cycled tank with some established algae. Adding them too early is the most common reason they fail.
How many otocinclus should I keep? Keep at least six. They are social and far more active and confident in a group.
Do I need to feed otocinclus if my tank has algae? Yes. A clean tank rarely grows enough algae to sustain a group, so supplement with blanched vegetables and algae wafers.