Otocinclus are tiny catfish with a big appetite for algae. This aquascaper favorite seems ideal as an algae cleaner for nano aquariums, but there’s a little more to its care than that. These small cats need some pretty specific care. If you’re willing to provide them with what they need you’ll have a fascinating addition to your aquarium!
Keep reading for everything you need to know about keeping Otocinclus catfish.
The otocinclus catfish is known by a variety of names, such as oto, oto catfish, otto cat, dwarf oto, dwarf suckermouth, dwarf sucker, and algae scraper.
|Tank size||20 gal (75L) minimum|
|Temperature||72-81 °F/22-27 °C|
The two most common oto catfish species typically found at your local pet stores include Otocinclus macrospilus and Otocinclus vittatus, which look very similar to a beginner’s eyes. Many stores sell/mislabel them as Otocinclus affinis, although this particular species is rare in the hobby.
The most beautiful species is considered to be the zebra Otocinclus, which has dark and light vertical stripes. Given how desirable it is, it’ll also put the biggest dent in your wallet to buy!
Oto catfish are native to and found in South America in small to medium streams with vegetation and moderate flow for oxygenation.
To help your fish feel more at home in your aquarium, the tank should have a sandy substrate, and plenty of plants and woods for hiding in. A powerful filter with lots of media for that sweet beneficial bacteria and a strong flow for aeration is a must.
Otocinclus catfish grow to be about 1 ½ to 2 inches (3.8-5 cm) in size. They have large eyes and are typically olive-brown in color with darker stripes along their bodies and blotches near the caudal fin. Female otos tend to be larger and wider than males of the same age.
Oto catfish are often confused with other similar-looking fish, such as Siamese algae eaters, Chinese algae eaters, and Siamese flying foxes.
Before you think about adding otocinclus catfish to your fish aquarium, which should be at least 20 gal/75L, it’s highly recommended to have a well-established and mature aquarium with plenty of algae, especially soft green algae. Although we all love sparkling aquariums, you’ll have to resist using your algae scrubber since algae makes up much of an oto’s diet. They won’t eat green spot algae (GSA), although some hobbyists have reported that they may graze on diatoms (brown algae) and biofilm.
While many people recommend 10-15 oto catfish for a 20-gallon setup, this particular combination won’t likely result in the consistent algae buildup needed to keep the otos well fed. Although you may be tempted to fill the tank with fast-growing plants to make quick hiding places, you should stick with slow-growing plants, such as Anubias and Java fern, to give algae a chance to grow. Use ceramic tubes such as these as hiding places instead.
Many hobbyists warn about how sensitive Otocinclus catfish are when adding them to an aquarium, even a well-established one. Their high sensitivity is often blamed on how the fish are captured (often using cyanide) and shipped from where they’re caught or bred. While some hobbyists attribute the mass die-offs often experienced to poisoning, overcrowding, and poor water quality, others also think that the fish starve because of how often and much they have to eat.
Even in an adequate setup, the effects of the above may cause losses in the first month of the fish being in their new home. It’s unfortunate, but most people agree that if the otos survive the first month, you should be set.
Because they are small and peaceful fish, Otocinclus catfish are best kept with other peaceful species such as the fish on this list. If you keep dwarf shrimp, they’re an excellent choice since otos have not been reported to eat baby shrimp.
Other fish that may do well with otos include small rasboras and some tetras. As long as the selected species are peaceful and can thrive in similar water parameters, they may do well with otos. Anything that’s large and aggressive should be avoided to prevent the otos from becoming stressed or eaten.
As mentioned above, if you want to keep your oto catfish chunky and happy, you will need to let that delicious (but often hideous) algae build up! Most hobbyists report that their fish will only eat algae, which is a major reason why you should let algae take over your tank before considering buying otos. Even then, they’re very efficient algae cleaners and will make very short work of the mess.
To prevent the fish from going hungry, you can leave the aquarium light on for 12 hours or longer to encourage algae growth. You can also purposely grow algae on other decorations or filter media to help feed oto catfish as needed. For example, leave rocks or ceramic rings in jars with plenty of plant fertilizers and excessive sunlight. Even then, it can take months for enough algae to grow for your oto catfish to happily feed on so make sure you’re prepared.
It seems like many hobbyists don’t have much luck with feeding their oto catfish anything but algae. Some people say their otos will eat vegetables or wafers, but it’s painfully obvious that an oto’s first choice is algae. If you’re not prepared to meet their dietary demands, you may be better off keeping Corydoras instead since they’re less picky.
Oto catfish are known for being active during the day and having lots of personality. They are high-energy fish that can dart quickly around the tank, which is why a larger tank is recommended. They’re also a joy to watch as they graze along the glass, giving you a chance to see their sucker mouths hard at work.
Many new owners make the mistake of only getting one or two oto catfish, but they thrive in larger shoals. The larger numbers make them feel safer, so you’re much more likely to see them out.
While breeding Otocinclus catfish is not impossible, it’s difficult. Those that have enjoyed success often say that they didn’t even know their fish spawned until they saw the new additions!
Most of the spawning process is done out of sight with oto catfish seemingly preferring to lay eggs on the leaves of plants. Interestingly, although otos almost exclusively eat algae, it’s been noted that feeding high-protein live foods such as brine shrimp and grindal worms seems to help with triggering spawning.