well let me tell you a little story about my watchmans. I purchased them as a pair from the LFS. When they were at the store they were always together, so it looked like a true pair. When I get them in my tank, they hate each other. A week goes by, and they are at opposite ends of the tank, and are not on "speaking" terms. A couple days later I add a
pistol shrimp, and with in one hour the 2 watchmans and pistol are sharing the same hole.
It is hard to say if they will pair up or not, it might happen, or it might not. You don't have to have a pistol shrimp for them to pair up either. In fact the pistol and gobies might not even pair up.
So basically, there is no certain answer to the whole pairing thing.
