Last Updated: 10/4/17

Quick Information
Description
Setup and Water Preferences
Sexing
Breeding
Problems with Keeping Ottos Alive
My Ottos and Their Photos
Links and Photos

Common names: Otocinclus, Otto, Oto, Pygmy Suckermouth Catfish, Dwarf Sucker
Scientific/Latin name: Otocinclus affinus (other similar species exist, like O. vittatus and O. vestitus)
Maximum length: 1 to 2 inches
Colors: Natural, black
Temperature preference: 70 to 80 degrees
pH preference: 6 to 7
Hardness preference: Soft to moderate
Salinity preference: Low
Compatibility: Excellent (may suck on large fish like discus and goldfish)
Life span: 3 to 10+ years
Ease of keeping: Moderate
Ease of breeding: Moderate to difficult

Otocinclus vittatus are often called ottos. There are half a dozen available similar species including O. affinis and O. vestitus. I am not sure which species I had before since they are gone now but O. vittatus is supposed to be most common in aquarium stores. The ottos that I got on 6/1/01 appear to be O. affinis. The main visual difference is that O. affinis has more of a spot at the base of the tail (caudal penducle) than O. vittatus. Ottos are small, suckermouth catfish that eat algae. Most come from Brazil. Unlike most other algae-eating catfish, ottos will not usually eat your plants. They, in fact, clean algae off of plants (plecostomus are better at removing algae from the glass). Ottos grow to about 1.5 inches at most so they can live in small tanks (10+ gallons). Ottos are great fish for planted tanks with non-aggressive fish. They are very delicate and die easily. It is best to get them in groups of at least four. Usually some die but the survivors can live for years. See below for more information on keeping ottos alive.

Ottos like slightly acid, soft water with lots and lots of plants. They prefer temperatures from about 68 to 79 degrees F. Even more than most fish, they need very clean, well-filtered water. Ottos should have driftwood on which to chew; the fiber helps with their digestion. They are very sensitive to medications; some of mine have died during treatments. Otocinclus like swift currents in part of their tank. Ottos are reported to be nocturnal but my old bunch were active most of the time. The ones I got on 6/1/01 seemed to just lay together in a clump during the day and hid. At night, they did come out so that bunch seemed to be more nocturnal.

Feeding:

They eat soft algae as their predominant food, off of live and fake plants, ornaments, and other surfaces. For supplemental feeding, one can use algae tablets (made for plecostomus) with sprirulina and sometimes vegetables. Quarters of cucumber and squash or romaine lettuce can be fed but some aquarists report no luck. Some ottos will eat live or frozen small worms (white worms, tubifex), small brine shrimp, and insect larvae (mosquitoes or bloodworms). A healthy otto should have a continually full belly. At least one person has reported that their otto ate some of their aquatic plants, specifically anacharis but this is a rare occurrence.

Females are larger, rounder, stouter, and fatter than males.

If you have lots of plants, lots of ottos of both sexes, and good water to their liking, they will lay eggs on the plants. Sometimes they will lay on rocks, glass, and other surfaces. The few eggs hatch in about two to three days. The fry need very tiny food to eat. Surface algae is the best food. Ottos are reputed to breed similarly to corydoras catfish (see my panda cory page).

Information on raising and feeding fry can be found at my breeding and fry care page.

On 10/22/06, Derek sent me some photos of his otocinclus when they were spawning. He saw them spawn in the T position that corydoras catfish also use. He got fry but none of them made it to adulthood. The photos are not good quality but still may be worth sharing.
Spawning ottos
Spawning ottos
Spawning ottos
An otto fry

People often have trouble keeping newly purchased otocinclus alive. This is due to a number of reasons. First, most ottos are caught in the wild so they have to suffer long trips to get to the aquarium store. Then, often the stores do not take good care of the fish. They may keep them in clean tanks with nothing to eat but whatever prepared foods that the care giver dumps into the tank. Ottos prefer to eat soft algae and will not do well if they do not have any. So, by the time someone buys a few ottos, they are often weak and starving. If they are then added to a tank without algae, they soon die. If the tank does in fact have algae, the ottos may eat most of that in short order and then starve, even with supplemental feeding. While ottos prefer to be in larger groups, it is important not to add too many to a tank. In a tank heavy with soft algae, one to three ottos per 10 gallons is fine but if the tank is too free of algae, it may not support more than one otto per 50 gallons. If you cannot support at least two ottos, do not get them as a single individual will waste away for lack of companionship [That said, my last otto lived alone for his/her last seven years!]. Often, after a batch of ottos are added, 20-80% of them die but the survivors may live for years since they have reached a sustainable population based on the algae and other food available. Die offs of new otocinclus are also common due to their desired good water quality and sensitivity to many medications. Only add ottos to established tanks with good water quality and some attached algae.

As of 6/13/09, I have no living ottos. As of 3/12/02, I had one otocinlus left in my 50 gallon tank. Update to 12/19/03 and 10/17/07 and that one otto was still alive! The poor dude had lost most of his fins but he still was sucking around after 6 years! They just do not do well in my tanks despite tons of algae so I will not get any more. That last otto died around 6/11/09 so I had him/her for eight years!

I had a few otocinclus years ago in my 20 gallon tank. When my goldfish died, I re-did the tank for small fish and got some more otocinclus. There were then up to 8 otocinclus in my 50 gallon tank. They appeared to be Otocinclus affinis. When I got them on 6/1/01, most were missing parts of their tail fins, and one was missing an eye. I hoped it was just physical damage from which they recovered. They went right to work and cleaned up most of the brown algae (diatoms) at the bottom of the tank. For some reason, they did not seem to want to go higher in the tank to eat the green algae on the driftwood at the top of the tank. They did an excellent job of cleaning off the leaves of the live plants.

On 8/1/01, I counted five ottos at once so I think that is how many there were. I saw the one without the eye on 8/4/01. I believe up to three of them died. The five survivors were plump, and their tails had grown back. They seemed healthy and only came out at night. I guess this bunch was nocturnal now! Algae was growing faster than they or the Siamese algae eater and rainbow shrimp cared to eat it. It is strange that when an otto dies, you do not always find the body! With other fish that die, I find the body. Someone suggested that ottos must just taste really good! I have a feeling that they died in a dark spot that I could not see well (weekly during cleaning, I check such spots) and thus sat long enough to be consumed by the other fish and shrimp as well as bacteria and microorganisms in the tank.

On 9/1/01, when doing my weekly water change, I saw an otto with a huge stomach. It looked like it swallowed a small marble! The fish did not seem to be in immediate trouble but died within an hour of the water change. Since I use well water, the oxygen level drops for a short time. The otto was trying to surface for air but kept bumping into my net breeder which had baby panda cories in it. If he/she had just moved an inch to either side, he/she might have lived longer.

On 1/02/02, I found a dead otto in the tank which I removed. On 1/19/02, I counted four ottos at once! I pulled out another dead one on 1/22/02. It had the yellowish marble in its gut and popeye (tuberculosis again?). Another died on 2/2/02. It had a huge abdomen too. So, I am down to two ottos left as of 2/3/02. By 3/12/02, I was fairly sure that there was only one otto left. While its stomach was not enlarged, it did have severe fin rot. This made no sense to me since the other almost 50 fish in the tank were very healthy, breeding, and had no fin rot. Ottos must be more sensitive to certain bacteria that consume their fins. Since I had so little luck with ottos, soon I will have none (okay, it took seven more years before the little fin-less guy died) and probably will not try again.

Update 10/17/07: That one surviving otto is still alive.

I found that otto dead on 6/13/09 after eight years. He had been dead a few days but was alive a week earlier. I have no ottos left.

Photos of my Otocinclus:

Photos are listed from oldest to newest.

Ottos with a panda cory, 6/3/01.
Ottos, 6/3/01.
Ottos with a panda cory, 6/3/01.

Update, 9/30/06. You will note I have not said much about the ottos in about four years! Well, since that time, I have only had the one otto. Somehow, he remains alive. The little guy usually shows up next to the filter intake after I clean the tank each week. I finally got a decent photo of him (yes, I know it is not in good focus but you can actually tell it is a fish!). For probably three years now, he has existed with most of his fins eroded away. Ottos seem prone to such things. And yet, he lives on. I have had him now more than five years. He does not seem to be lonely without other ottos but I know better than to get more when they obviously do not do well in my tanks despite the soft water and good maintenance. Here is a photo of him on 9/30/06: my otto.

I got a better photo on 11/18/06 of my surviving, mostly finless otto, in his/her favorite spot next to the filter inlet tube: My otto.

My otto waiting in a bucket during the 50 gallon tank cleaning on 3/17/07 with a small rosy barb and the Queen Arabesque pleco. See the tank redo page for details from that day.

Otto sucking on the driftwood in the 50 gallon tank on 3/24/07.

Otocinclus affinis - 6 cute photos of Otocinclus affinis.

Planet Catfish - a UK catfish page with information on lots of catfish.

Catfish of the Month - information and pictures of Otocinclus vittatus.

Golden Otocinclus - photo of Otocinclus affinis and some information.

Otos - a few great, closeup photos of otocinclus. Note that this site may no longer work.

The Ideal Algae Eater? The Littlest South American Suckermouth Catfishes, Genus Otocinlus

Otocinclus.com - a web site dedicated to otocinclus.

Otocinclus Care

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