I had to remove a watchman gobi today. I have 4 of these, I don't remember how many years I have them but I got them as babies. These two pictured and one almost the same size and a much smaller one. This pair is spawning like they always are and the large male always chased the smaller male but it never seemed to bother him much. They lived together for at least 6 years. Now the male is much larger than the other male and he never stops chasing him. I have seen him cowering in a corner for the last week but I could not catch him. Today the large male chased him so much that I was able to grab him with my hand because he was practically beat to death and could not hardly swim.
I have him in a small tank with some antibiotic because his fins are all torn as is his mouth. I will nurse him back to health and he will live for a while with my burrfish. I hope he doesn't eat him.
Then if he recovers fully I will probably give him away.
Unfortunately, fish in great health spawn but when they do, they will not tolerate other males and will likk them. So it is a good sign with a bad outcome.

Its nuts isnt it. I had to remove one of two brother angelfish, even at 11" they fought like kids, ones eyeball is all falling out and his mouth was torn up but recovered from that, the other one barely has a mark on him less his mouth area.