Otocinclus Catfish - Otto Cat

Updated August 5, 2019
Author: Mike - FishLore Admin
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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 aquarium 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.



There are about 22 species of Otocinclus with some of the more commonly kept pictured in this article. Scientific names are below the images.

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.

Otocinlcus Notes From FishLore Members:

(credit: armadillo and MamaM)

Also see the Oto Caresheet on the forum.





Otocinclus Catfish Care Details

Scientific Name : Otocinclus sp., over 22 species known

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 in well oxygenated, moderate or slow flowing water where this is plenty of algae to eat.

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)

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:

Hikari Algae Wafers
Nori Algae Sheets

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

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

Photo Credit : Photos copyright JJPhoto.dk

Site References :

Otocinclus Catfish Comments

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 them. Suppliers often mislabel or misidentify Chinese Algae Eaters as otos. 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 one 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.

Still have questions?
Jump on the forum and ask your question!
Go here: Otocinclus Catfish Forum

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