What Are Otos?
Otocinclus, the dwarf suckermouth catfish, is a popular genus of algae-eating catfish. The 17 species of Otocinclus (often called Otos) are often kept in hobbyists' aquariums to control algae. Unlike their large cousins, the Plecos, Otos remain small and are not boisterous enough to cause damage to plants.
Although they are often purchased solely for algae control, Otos are social and should not be kept in groups of less than three. They are native to South America east of the Andes mountains, in streams that drain into the Amazon, Orinoco, and Paraguay/Parana rivers, and in streams that drain into the Atlantic in southeastern Brazil. They are notably absent from the Guianas.
All About Keeping Otos
This guide discusses the following aspects of the Otocinclus genus:
- Purchasing Considerations
- Breeding Considerations
Otos are small—they range in size from 16.5–43.8 mm (0.6–1.7 inches), not counting the tail. Females are 10–20% larger than males and have a broader body, especially when they are in breeding condition.
Otocinclus are herbivores, feeding mainly on algae. The ideal tank has a lush growth of algae for them to feed on. Driftwood tends to support a healthy growth of algae for them to consume. Since it's difficult for them to browse the algae all the way down on a rough surface like wood, it's likely that there will always be something to eat on a piece of driftwood.
Aquariums often do not support enough algal growth to feed a school of Otos, so it may be necessary to supplement their diet with blanched spinach or zucchini. Food that has been dipped in boiling water or microwaved for a minute or two appears to be more attractive to Otos. An algae clip or a rock can be used to hold the material in place.
Sinking algae wafers are also a good way to get some more protein into their diet; however, since these wafers usually have a significant amount of shrimp, they are also attractive to other fish. In my main tank, the Otos rarely get at the algae wafers—the more boisterous Corydoras catfish keep the Otos from trying to get at the food.
3. Buying Otos
Most Otocinclus are wild-caught. Since they are vegetarian and need to eat almost constantly, mortality rates are high in transit. They may be starving by the time they get to the pet store, where they are often fed unsuitable food. Combine this with the added stress of a trip home from the pet store, and you end up with a fish that has a reputation for dying easily.
To minimise the risk, try not to buy fish until a few days after they arrive at your local pet store. Pick the healthy fish—the ones that are swimming around, looking for food on the gravel and glass, and schooling with the other Otos in the tank. Pick ones with rounded, not sunken bellies. Choose carefully.
Gary MacDonald (see "resources" section below) recommends that you bring a "snack" for the trip home. A piece of skinned cucumber or zucchini would make a good choice. It's always a good idea to bring a darker bag to put your fish bag in—this minimises the stress of the trip home.
4. Breeding Otos
Breeding Otocinclus requires a heavily planted tank. Spawning is triggered by water changes using water that is a few degrees cooler than that temperature of the water in the tank. As with Corydoras catfish, Otos appear to use a "T-position" when breeding. Gary MacDonald's article (see "resources," below) is an excellent resource. Another account of spawning is available online at PlanetCatfish.
5. Species of Otocinclus
In his 1997 monograph on the species, Scott Schaefer recognised 13 species of Otocinclus:
- O. vestitus,
- O. afinis,
- O. flexilis,
- O. vittatus,
- O. hasemani,
- O. hoppei,
- O. mariae,
- O. macrospilus,
- O. bororo,
- O. caxararz,
- O. huaorani,
- O. mura, and
- O. xakriaba.
Since then, four new species have been described:
- O, batmani,
- O. cocama (the zebra Oto),
- O. mimulus, and
- O. tapirape.
This brings the total up to 17 unique species.
The definitive monograph on the genus Otocinclus was published by Scott Schaefer in 1997:
Schaefer, Scott A. 1997. The Neotropical Cascudinhos: Systematics and Biogeography of the Otocinclus Catfishes (Siluriformes: Loricariidae). Proceedings of the Academy of Natural Sciences of Philadelphia 148:1-120 (JSTOR subscription required).
Macdonald, Gary A. 2008. Oto Pilot: Buying, Keeping & Breeding Otocinclus Catfish. Tropical Fish Hobbyist, February 2008.
kip on February 05, 2011:
i read somewhere that if your oto starts to spend a lot of time at the top of the tank its because the water quality is not good, they apparently do not tolerate unclean water so regular small water changes are advised.
Jay on January 26, 2011:
Irene: Your otos are most likely starving to death. There is an algae/microbe line above the water line. The otos were probably leaving the water in search of food.
Additionally, I have never had any issues with these fish dying. Was surprised to see them listed as delicate. My current oto is nearing 3 years old. When I get some more algae in my tank I will buy him a friend.
Pat Menken on September 05, 2010:
I am somewhat new at raising ottos, but I have read several places that if you can get the ottos to survive more than a month, they will likely thrive a long time (barring any major or stupid accident). Driftwood is highly recommended, but I do not have any in my tank. Plants are highly recommended, but the one plant we had died (and we removed it). My tank (10 gallon) has lots of large gravel and several sea shells (about a dozen). For a while we used a 60 watt bulb light (until it burned out). We then switched to a 100 watt bulb and could visibly see lots of algae start growing on the tank within a week. We eventually were able to afford an aquarium light that now uses 15 watts flourescent. I also have black mollies and several really small snails (23 at last count). I didn't realize that the mollies eat algae also. WE now have an army of algae eaters. Weirdly, our original otto female will not even consider eating the algae tablets we bought. When we got 2 new ottos, they seemed to love it as a most wonderful treat (unfortunately, so do the mollies). The biggest problem I saw, was trying to keep the right temperature for all the fish. After some quick consulting on the web, I came to reason that 77F (25C) would be about the best temperature. Later, I learned that 77F (25C) is also the optimum breeding temp for ottos as well. Even tho the local Pet Smart (where we bought our first otto) (and several other local stores) are out of ottos... We already had my female trying to attract a mate when she was the only otto. When we added the 2 new ottos (1 female and 1 male), i had hoped they would spawn together. I accidentally threw away the first egg set from the original female while cleaning out 50% water replacement (not knowing what this clear gel was). Now with 3 ottos, there are 2 different locations of this clear gel. I am not entirely sure that our male is old enough to perform his adult duties. He seems to favor the smaller female (the one we bought with him). The 2 biggest reasons for an otto to die are : 1. there isn't enough algae in the tank, 2. The capturing method or other stress on the animal caused severe harm to it (most likely its liver). In parts of the world, they use cianide or other chemicals to slow the ottos down and make them really sluggish (and easier to catch). This has severe negative effects on the ottos health. Places using these methods are endangering the life of the otto (and the stress of a new tank only seems to speed up the process). I would recommend you get your otto from a different store. Ironically a week later, (the store we bought our original otto and mollies at) had their fish come down with ick. Our otto never showed any signs of ick. The mollies came down with ick and they have never been the same. They survived the treatments but have permanent scars. I later read that ottos are also sensitive to ick treatments and other medicines (I suspect this is probably referring to the ones who have bad livers). Our 3 ottos (though they each choose a different territory in the tank) do often hang out with eachother and can most often be found within a 2 inch radius (all three of them). My observation is that ottos can live alone, but seem to prefer friends. We had 2 neon tetras with the original purchase of fish, however one neon died within 24 hours and the other neon got so lonely (even the mollies wouldn't play with it), that it simply quit eating. It died of loneliness within a week. Hope this helps you guys get some ideas about ottos. I got my information by using google and researching several sites (and of course from my own experiences as well). Good Luck. p.s. even the mollies have successfully bred recently.
Irene on April 05, 2009:
To whom it may concern,
Thank you for sharing your knowledge and expertise on otocinclus vittatus. I have learned much valuable information from your website. I have raised these fish but sadly with no success. I do not want to give up on the possibility of raising these fish successfully so I am trying to research as much as possible about them as much as possible until I plan to get more. At one time, I had one baby successfully survive for about a week until it disappeared. I assume it was devoured by one of the other fish in the tank. The full grown ones did not survive much longer then a month. A couple of times I saw an otocinclus vittatus move above the water line to suction against dry part of the glass aquarium. I am not sure if this was normal. It seemed strange. One of the fish that did this I believe died as a result of being dried out. Anyhow, thank you for providing thorough information about this interesting fish. I would appreciate any further advice that you may provide me regarding how to raise them.
forlan on March 23, 2009:
nice hubs. i must learn from you
Ramon on March 17, 2009:
Nice to know about how stressed they are in transit to pet store.
cole on March 12, 2009:
i have 1 otto catfish who i keep with 7 tetras and 1 african dwarf frog in a 10 gallon tank and they're getting along great.
Frank on June 29, 2008:
I didn't know that the little otos was a social fish. My mom has one. I will have to tell her so she can get a couple more. Thank you for that helpful article.