I have 2 YWG paired with their own pistol shrimps. They live happily in their own tunnel systems and have staked off their territories. Every now and then the larger goby will go show the smaller goby who is boss and then go back to his home. I also have a sand sifting goby and the large YWG will chase away when the SSG gets to close to his house. But now, the larger goby spends most of his time outside of his house. He goes to the side tank wall and looks as if he is trying to get to his reflection. Swims up and down the side tank wall looking at himself. Is he vain? He is ignoring food and the other gobies as well. My water parameters are good. All the other fish are eating well. My first thought is he/she is wanting to mate. But not sure. He doesn't look sick or thin from not eating. Still looks healthy. Any ideas?