Please be Careful! Though at first glance the Oto cats (South America) kind of look like the Chinese Algae Eaters (Asia), they are two totally different fish! The CAE in it's early stages act like the Oto. But the CAE get BIG really fast and are actually DANGEROUS to slow moving peaceful fish, as they cling to them, feast on them, and otherwise make them vulnerable to disease and death. The CAE does NOT follow in its name's sake, and most of the time are mistaken at shops by those who buy them as Algae-eating. Oto's rarely cling to other fish.
I have one oto in my 40 liter with a betta, SAE, and mystery snail. The interaction between the oto and SAE is interesting to watch. The SAE is three times the size of the oto. They argue over food, which the SAE tends to win, but ends up sharing anyway. And, as some have described, the oto will try to suck on the SAE. Though, the SAE doesn't seem to mind, as he turns on its side to let the oto do whatever it thought it was trying to do.
I have two Oto's and they are always over the glass cleaning/eating. This past week they have been pairing like a couple of muskrats - circling, playing tag, no aggressivity. Then one rests on one of the aquarium rocks - egglaying unknown. The tank is a community 40 L. It is bright, and with a lot of water motion and aeration, as if a stream bed (which they allegedly prefer to still tanks). They make up in glass and appliance cleaning (heater, filter intake, thermometer) for what they don't do on the bottom. That is left to Albino Corys. Serpae Tetras in group from regional South America share the tank.
I'm a big fan of these lovely little fish, I have some that must be 9 or 10 years old now and are some of the biggest I have ever seen. What I can say from experience is they definitely do better in planted tanks with soft water, but are otherwise very hardy and easy to keep. It seems to me there is still a lot we don't understand about these fish, when I was collecting fish in Loreto Province, Peru we came across some places with floating weed (mostly water hyacinth) where there were thousands of them, and other places you never saw them at all. What amazes me is that we (aquarists) don't even know the proper scientific name of the Otos we are keeping 90% of the time.
I love these little guys. I have owned a few of them, and they do an excellent job of algae cleaning. The only problem is that none of mine have lived as long as I think they could have, but that may be just the situation in our tank. These are among the cutest suckerfish and because they are small, I can easily fit them into a small 40 L tank like mine.
I bought 1 oto after I got rid of my CAE. He was doing fine for a while, but then I realized he was getting sort of lonely and sluggish. He would isolate himself from the guppies that he used to play with. I got 2 more to play with him and now they're all having a blast! They school together and it's really fun to watch. The hardest thing in keeping them healthy is giving them enough food to eat. As long as they have a plump, round belly, they're fine. If you put some lettuce or algae wafers in your tank (which you'll probably eventually need to do) be patient with them. They have tiny weak mouths so they need to wait for the food to soften up.
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