The species is however only imported from time to time, and is collected from Brazil, notably the Rio Negro, Xingu, Araguaia, Venezuela and the Orinoco.
It is common for these fish to be imported with what looks like black spot disease. These black spots are scattered over body and fins and are smaller than a pinhead. This is also common in wild-caught Angels and geophagines. Although unsightly, these aren't really a problem - they are probably just "glochidia" - a larval stage of a freshwater mollusc.
What happens is that free-swimming larvae attach themselves to a host (the fish) and wait until it is swallowed whole by a particular bird. The mollusc larva then travel through the bird's digestive system, which triggers metamorphosis, before finally being excreted in the bird's faeces back to the river bed...
So you don't have to worry about clams appearing in your tank! As the fish grow, these spots will become less as layers of skin tissue flake off. So don't let this problem get in the way of your enjoying this fish - unless you have a kingfisher or fish eagle in your living room.