I have a pair of clownfish, with one being bigger than the other, I do see the smaller one having nipped fins from time to time but its nothing extreme. I did see that my lfs will have a pistol/yasha goby pair in stock but not sure if its a good idea to keep them in the same tank, its a 20G AIO red sea and has been running for a long time. i thought it would be a good idea since the pistol and goby will be on the bottom portion of the tank hidden from the open water clowns but again, not sure if its a good idea to keep them in the same tank. I dont see anything online about it so im not sure.