Also called a suckermouth catfish, plecostomus (or pleco for short) are large algae and dead fish eaters native to the tropical freshwaters of Central and South America. They are occasionally seen in the southern U.S., but they are considered a harmful invasive species. The term plecostomus means ?folded mouth,? a fitting name for a fish that literally has a mouth that folds downwards, perfect for sucking down food along the surface of rocks and other structures. They can grow to be a couple feet in length, and are known to be rather territorial.