I have a freshwater mussel and my girlfriend's brother has several in his tank, if freshwater clams are anything like them then they are dead easy to look after, they eat nothing more than the natural waste provided by a lived in aquarium. I.E: left over minute food scraps, fish waste & algae floating around therefore being a great help to keeping your tank alot cleaner. They are also cool to watch as they tend to move around a bit. On the downside they tend to mess the heck out of your tank, tossing plants out of the way, knocking over ornaments, digging trenches in the substrate. The way they use their foot to pull themselves over the ground is utterly mesmorising though and reason enough to forgive them.