Sucker fish, also known as algae eaters, are an important part of freshwater aquariums. They eat algae and other detritus from the bottom and sides of tanks, helping to keep the tank itself and the water clean. They have round mouths and large lips; they like to cling to the sides of tanks and the undersides of tank decor, eating as they scoot along. Sucker fish tend to do best in tropical tanks.
The most widely available and common type of sucker fish is the plecostomus, or pleco. They are valued for their efficiency in cleaning up algae and excess fish food, as well as for their hardiness and longevity--unlike other sucker fish, plecos can adapt to cold water aquariums, such as goldfish tanks.
The panaque is a close relative of the plecostomus. They tend to be more decorative than their cousins, though, having horizontal stripes down their bodies. They are less commonly found than plecos, and tend to be more expensive.
The otocinclus is also a catfish, but is much smaller than a plecostomus or panaque, usually getting to be only a couple of inches long. Unlike the panaque and plecostomus, the otocinclus likes to be kept in pairs or small groups.
The sucking loach is also known as the Chinese algae eater. They have long, thin bodies and short fins. They are very efficient algae eaters, and some people prefer them to plecos because of their smoother looks. Sucking loaches can be somewhat territorial, and may chase other fish.
Siamese algae eater
The Siamese algae eater looks much like the sucking loach, but has a somewhat shorter, stockier body. They, too, are efficient cleaners, but tend to be rather hard to find in commercial fish stores.