It's a yoyo loach. I've read they change patterns when they get older, although I have a couple of small ones that already have the none "yoyo" patterns.
taken from loaches.com:
"Body markings can be very variable in this species, and there is a marked difference between juveniles and adults. Adults develop more "in-fill" of the juvenile markings to a point where the whole fish may be reticulated, hence one of its common names."