(Loricariidae Family)
The Otocinclus (oto, dwarf suckermouth catfish) is an excellent addition to any tropical freshwater tank. They like to live in groups and grow to a maximum of 1-2 inches. They LOVE algae and make a real dent on any tank with an algae problem.
There have been reports of difficulty in keeping them alive, they must have food available all the time, they need to constantly eat. Starvation is a common cause of death in Otos. If you do not have enough algae, supplement with zucchini, spinach, cucumber and algae wafers.
Breeding Otos in captivity is hard, there are very few reports of successful attempts, consequently a lot of those found in pet shops are wild caught and may have already suffered enough of lack of food to only survive a short time in your own tropical tank. Do not be afraid to question your fish store on where they have sourced their Otos from and if they have been well fed! Look for little round tummies, a fat oto is a happy oto!
There are several species of Oto. The most commonly found is O.Affinis, the golden oto, it's brown on top with a white belly and a black stripe running along both sides, it prefers soft water, but mine have thrived in hard London water. Most fish will adapt to hard water if they have been raised in it.
Others include the following Zebra. More are being discovered and named by the year. It's rare to find anything other than Affinis in regular stores though.
Here's some other useful sites:
Otocinclus.com
Planetcatfish.com