I have 2 clown loaches purchased at around the same time, about 3 years ago. Lately one has grown larger than the other and has grown a large belly and has gone a darker colour than the other. The second is straight along it underside and is definitely brighter in colour. Both appear happy enough. They're in a general mixed tank, with a couple of Plecks (that have grown a bit larger than I'd like) and a few smaller barbs (golden barbs,etc). I've never had any problems with infections or anything else. I did wonder if one loach was pregnant but I've read that they are virtually impossible to breed in a small tank like mine. Any ideas?