In my 120G all male tank I did 2 groups of 6 on stocking about 2 weeks apart. In the first group, the dominant fish was my 4" yellow rock Kribensis. He even killed off my Blue Ahli that was about an inch smaller than him. For my second stocking, I wanted to look into a fish that was larger than the Krib, but not an agressive A-hole, in the hopes he would become a gentle tank boss. I got a nice 6" Star Sapphire. It seemed to work like a champ. The Rock Krib tried to assert himself and quickly realized he had been knocked off his perch. All has been great for about a week now, tank is very peaceful and everyone getting along great. Today I am starting to notice the Krib not acting right, he is sort of hanging out in the corners etc. He looks perfectly fine appearance wise, no nipped fins, no obvious battle wounds, and I haven't witnessed anyone messing with him. Not sure what to make of it. Do these fish go thru some sort of "depression" when they lose the top spot in a tank?