Written by DSkidmore
New Otos from the pet store have a high mortality rate but after they settled in, though, they are a joy to have. They have very interesting social behaviors, moving around the tank in groups
Synonyms: Otocinclus mariae and O. affinis
Common Names: Oto, Otocat, Dwarf Sucker Catfish
Origin: Tropical South America
Main Ecosystem: Bank side or floating brush islands in large tropical streams.
Care: Best kept in heavily planted aquariums with a decent amount of wood to hide under and harvest algae from. Some suggest a “leaf litter” covering over a sandy substrate, and others recommend a large rounded stone substrate.
Temperament: Docile, somewhat timid. Playful with others of same species. Best kept in groups of six or more. Sometimes observed latching on to slow-moving fish — this may be a sign of starvation rather than aggression.
Diet: Herbivore. Some sources will claim they need wood in their diet, but this is not scientifically supported.
Care: Healthy Otos should have chubby bellies and should be pooping constantly. Once acclimated to the community tank, supplement the algae/surface film diet with veggies whenever necessary to keep them chubby. Any large filter inputs should be screened to keep them out, as they love areas of high current.
pH: 5.5 – 7.5
Temperature: 21 – 26°C / 70-79°F
Hardness: Low to high — Native waters are mineral rich, but they are tolerant of softer waters.
Potential size: 2”
Water Region: Vertical surfaces, plant leaves, mid to lower region of the tank.
Activity: Varies by situation. In a busy tank, they will turn nocturnal and come out of hiding when they feel most comfortable.
Lifespan: 5 years, although this is a challenging fish to keep for a full normal lifespan.
Color: Brown, Black stripes, Silver belly.
Mouth: Suckermouth – Downturned
Sexing: Females are larger than males of the same age, which have the same diet. (Since most Otos are wild caught, this is not a very helpful method of sexing.) Sometimes eggs can be seen in the stomach of the female. Mostly sex is only obvious by behavior during mating.
Acclimation: When you bring this fish home, be sure to fatten him up well in the QT before subjecting him to the busy chaos of a community tank. Use an algae culture and/or a sinking herbivore diet. He is likely to be famished from his time in the LFS. He should also receive a pre-emptive anti-parasitic treatment in QT.
Breeding: There has not been a great amount of success breeding these fish. They will lay eggs on the leaves of plants in out-of-the way areas. Often the first indication that breeding has occurred is when surviving fry appear in the tank. Feed the fry algae culture and infusoria until they are able to accept vegetables. Some have reported that a high current is helpful in getting Otos to breed.
Comments: I had a few Otos in my old 10 gallon tank. New Otos from the pet store have a high mortality rate, and I had to take advantage of the guarantee right off the bat. After they settled in, though, they were a joy to have. They have very interesting social behaviors, moving around the tank in groups. My batch did not turn nocturnal as some do, but liked to lie out in the open on my crypt leaves, almost appearing to sunbathe. They were excellent at carefully peeling the algae off of the plant leaves without harming the plants. Their fragility came back into play when I swapped out my old filter in order to conduct a repair. I suspect I had an undetected ammonia spike as a result. All my Otos died within a week of switching the filter. I hope to try again now that my 75 gallon planted aquarium is maturing enough to have a healthy crop of algae.