So, yeah, got myself a derg now, at least partially aquatic fellow too. Got the looks down, but still have to think of a name for him, I'll edit this description, and also the tags, when that gets figured out. Edit: Thought of a name, Veltinar!
As for his size, yeah he's a pretty big lad in this image, though the actual size will of course vary a bit in pictures due to a variety of factors, mostly being what would look better. X3
