Ottos playing in the flow
The otocinclus catfish is a fantastic addition to a freshwater tank, particularly a smaller sized one. As one of the smallest catfish available, they don’t take up much space and are an essential component of an aquarium “cleanup crew” along with snails and amano shrimp they do a nice job of keeping plant leaves free from algae buildup. They don’t come in any splashy bright colours, but they have piles of personality!
Ottos are incredibly peaceful and shrimp-safe
Ottos eat algae and biofilm and are completely non-carnivorous. This means they are perhaps the only fish that is 100% safe to freshwater shrimp of all sizes. With any other fish if you have shrimp, particularly smaller ones such as juvenile neocaridinas (cherry shrimp) you are taking an awful chance having them in the same tank with fish other than ottos.
Otocinclus are semi-social
Ottos have a reputation as a social fish that prefer to be kept in groups of at least six. Whilst they don’t “school” or “shoal” as such, I have noticed that during the day, when they rest, they do tend to loosely hang out together. In the evenings when they become more active they mostly do their own thing by themselves.
I suspect that schooling represents mostly a stress response. Ottos are thought to be “delicate” and prone to stress from a variety of sources, particularly from rapidly changing environmental conditions.
What do you feed them?
In the general case, nothing at all. They seem to survive just fine on the algae/biofilm component of a highly planted aquarium without requiring dedicated supplemental feeding. Of occasion I add an “Algae Wafer“, but I’m not sure the catfish ever actually eat these. Mostly they spend their time scarfing along the aquarium glass, or on the plants.