Aquarium Fish

Otocinclus Catfish - Otto Cat

The Otocinclus Catfish is a great addition to a peaceful planted tank and a small school of them can form a great algae cleanup crew. These catfish like to hang out under and on plant leaves as well as sucking on the tank glass. However, they can be a little reclusive at times and providing places to hide will help make them feel secure. Because they can be quite shy it's a good idea to avoid keeping them with overly aggressive tank mates or other fish large enough to eat them.

Otto cats are primarily herbivores so you will need to supplement their diet with algae wafers if you think they may not be getting enough algae to eat. Some hobbyists have difficulty in keeping them and it may stem from the tank not having enough algae present for grazing, improper acclimation, lack of hiding places, high nitrates and low oxygen levels. Stay on top of your water changes to prevent nitrates from getting out of hand and provide plenty of surface agitation (air stones or power heads) for gas exchange. For even better results, add your new catfish to an established tank that has already completed the aquarium nitrogen cycle.

Ideally, you should quarantine your fish before introducing them to your main tank so that you can monitor them for disease and also provide them with optimal water conditions and no competition from other tank mates for fish food. They may be stressed from transport when you buy them from your pet shop and quarantining them will help settle them down.

Notes From Fishlore Forum Members: (credit: armadillo and MamaM)

  • They are really poor acclimators. This means that they dislike changes, a lot! Changes in temperature, water parameters, transport, etc. When you've just got them from the shop, there are several critical stages. The first 24 hours are critical, then the first week, then the first month. If you still have them live and kicking after a month, then there's a good chance that the'll live to a ripe old oto age. It's super important when you first get them that you drip acclimate them. This will increase their chances. It basically consists in gradually adding drops of your tank water to their bag (which is floating on top of the water to get them gradually used to the temperature of the tank) over about 2 hours or so. You can use a syringe to slowly drip water water into their bag.

  • They like to be left alone. I don't mess with anything inside the tank aside from once/twice a week cleaning.

  • I recommend you quarantaine them for 2 weeks

  • They like extremely clean water. Please ensure there is not a trace of ammonia or nitrite, and that your nitrates are really low. I clean once/twice a week.

  • They like to school. The more otos you have, the more secure they feel.

Also see the Oto Caresheet on the forum.


Otto Cat Otocinclus


Fish Care Details

Scientific Name : Otocinclus vestitus

Common Names : Otto, Oto Cat, Dwarf Sucking Catfish, Midget Sucker Fish

Care Level : Easy but needs to be slowly acclimated (preferrably drip acclimated) and you must keep them in optimum water conditions by performing frequent partial water changes. Only add them to tanks that have completed the aquarium nitrogen cycle. They love heavily planted tanks!

Size : Up to 2 inches (5 cm)

pH : 6 - 7.5

Temperature : 70°F - 78°F (21°C - 26°C)

Water Hardness : 6° to 15° dH

Lifespan : 3 - 5 years

Origin / Habitat : South America

Temperament / Behavior : This is a very peaceful catfish and does well when kept in small schools.

Breeding : They can be difficult to breed in the home aquarium. They will lay eggs on plant leaves.

More Breeding Info: (credit: Armadillo)

  • They'll kind of 'smell' each other like dogs, and then the female will rest on a surface and the male will intertwine his body with hers. He's fertilising her eggs.

  • She'll lay her eggs all around the tank, not in one big clump. The good eggs are transparent with a bit of dark inside, the bad eggs are fluffy white. Do get rid of the bad eggs with a turkey baster as they're covered in fungus which could be detrimental to the rest of the eggs.

  • The male will defend the eggs, which is really cute. He just kinda stands watch around them.

  • If you want oto fry, you'll need to get rid of any fish in the tank that could potentially eat the eggs of course

  • After a couple of days, the eggs will disappear and you'll see some tiny wrigglers. If your wrigglers make it past a week, you have a good chance that they'll survive. The fry survival rate is really low.

  • A week or so later, she may lay more eggs.

  • The fry will eat the same as the parents (in my experience). I don't give them fry food as they'll not find it and it'll just pollute the tank

Aquarium Size : 20 gallon or larger.

Tank Mates : Many, given their peaceful nature. Avoid keeping with fish large enough to eat them and fish that are overly aggressive.

Disease : Freshwater Fish Disease - Quarantine all new fish before adding them to your aquarium!

Things To Watch For: Paleness. Paleness in an oto is a sign of stress. A lot of people report death within 24h of first noticing the discoloration. Stress can be caused by many factors including: excessive tank disturbance by humans, aggressive tank mates, not enough hiding places, not enough other otos, water parameters, temperature, etc. Buuuut, they are quite transparent fish, so if they are in brightly lit conditions against a white background, don't panick! Just look at them under normal conditions (natural light) to see if their stripe is nicely visible. If it is, then they're not alarmingly pale.

Sunken belly: it is imperative that they get a constant source of food. An oto with a sunken belly may already be on the way out.

Diet / Foods : Herbivores, you may need to supplement their diet with algae wafers. Here are some more good foods to use:

More Food Notes: (credit: MamaM on the Fishlore forum)

  • They need a really REGULAR food intake. Some can be condemned if they dont' get food in as little as 12 hours. Always leave food out for them if you're low on algae.

  • They need a lot of algae, so do consider setting up an 'algae farm' outside in your garden, or close to a window. All it is is a clean fishbowl covered with a clear top (to let the light through on top as well), and you put a couple of (clean) glass jars in there to grow algae on. When your jars are covered in algae, you can drop them in the tank. After a while, you can rotate your algae-covered jars from outside with your algae-cleaned jars from inside.

  • Do not forget to seed your algae farm with some waste matter by rinsing the filter in it. If you don't do it, algae take ages to grow. If you do do it, algae can grow in a couple of days but, don't overdo it or all your ornaments will be covered in algae.

  • Always leave a long strip of cucumber or zucchini (give them as big a surface area of the vegetable as there is space for, so they find it easily). Do remove it after 24 hours or so to avoid a nitrate spike from the vegetable rotting. I pretty much constantly have a slice in the tank, and constantly have an oto on it! Buuut, it took a while for them to get it. (well, a while, a week or so I think).

  • They're not averse to the odd algae wafer, although this shouldn't be their staple diet. In case they dont eat it, put it in a bowl inside the tank (not a plate, or it might fall in the substrate anyway). That way, if they don't eat the wafer after 24h, you can easily find and remove it (uneaten algae wafers can easily pollute the tank, sometimes causing nasty nitrate spikes).

  • Some are not so good at locating their food, or identifying something as food. Don't despair and keep trying (e.g. with cucumbers) by putting large chunks of the food always in the same place. They'll eventually get it. I always add my algae wafers in a little plate they've got in the aquarium. Now they know to check the plate.

  • I do add a frozen spinach leaf for something different (freeze the bag of baby spinach, then take one out and thaw a little and stick it in with a veggie clip to weigh it down... they LOVE it!)

Tank Region : Mostly middle to top.

Gender : The male is usually smaller than a female of the same age.

Fish Lore Forum : Otocinclus Catfish Forum

Site References :


From: 0morrokh
These little cuties also love spinach, zucchini, romaine lettuce, and brussel sprouts. Microwave or cook veges to soften them before serving. To keep them from floating, lettuce can be put in a vege clip, and the other ones tied on to something heavy with a rubber band, although cooking long enough will make them sink. Otos often die within a few weeks of buying for no apparent reason, due to suspected inhumane capture methods or lack of proper food at the store. However, if you can keep them alive for a month, you should be good to go.

From: Rachel
Just a word of caution when purchasing otocinclus. Suppliers often mislabel or misidentify Chinese Algae Eaters as Otocinclus. If your 'oto' gets much more than 2 inches it's not an 'oto' and you need to relocate the impostors as they are extremely aggressive to community fish and will literally suck a hole in their sides and they will die. You won't necessarily see the behavior at first as it is intermittent but it will happen sooner or later.

From: Thomas
Rachel - You are absolutely right about that! I thought I bought an otto but in fact it was a chinese algae eater! What tipped me off was it was attacking my goldfish which an otto cat would never do.

From: Sandy
I just love these little fish! I have 4 in a 10 gal. tank and they keep the algae down. I love watching them hang off live plants. One of my Otto's is very pregnant. I'm going to separate her from the others in the tank so she can lay her eggs peacefully. Since Ottos are mainly herbivores, any suggestions on fry food for them? Krill is usually used for the omnivores, but I'm not sure what to use in this situation.
Krill is mostly used for larger species to increase coloration. Maybe you meant to say brine shrimp? What if you got some aquarium safe rocks and put them in a tupperware bowl with tank water and set it in a window for a week or so and let some algae grow on the rocks? Take a few at a time and put them into your Otto tank and rotate them every couple of days so your ottos have a continuous supply of algae.

From: Fish Fan
We've had an otocinclus in a 10 gallon community tank for 2+ years. He is about 1 1/4 inches. He's been a great algae cleaner, even when the tank has gotten pretty bad. When using the pump for water removal take care to keep your eye on otto, because they don't stay away from it.

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