they are identical, we tell them apat by temperment, R2 is very bold and dominant, he is the first to do everything, D2 is very submissive, he is never out on his own, only with R2, and when together,D2 is always slightly behind. that is actually why there is 2 water bottle in the tank, because R2 is so dominant that if we dont have 2 of every resource, D2 wont be able to get near anything. apperently this behaviour is normal lol