I have a mystery wrass who is full sized when I got it at the beginning of this hobby 3 years ago, and she is close to 5" now. For those who have seen my tank, you know I also have a six line wrass which was pretty big. Recently, the six line grew even more, and it is between 2.5" and 3" now, and super fat. The mystery has been zooming around while being perfectly peaceful with the remaining 16 fish in the 120g tank (I know it is a little crowded, but I like fish in my coral tank, even though I have to deal with algaes recently). The six line has always picked on my mandarin but nobody else, even not the fire fish. Two days ago, when I feed the fish, I did not see the mystery, which usually is the first waiting at the food drop zone. Yesterday, after i fed, I saw the mystery stuck its head out of the rocks, looking really nervous. It then darted out for a piece of shrimp, and the six line immediately chased it. The mystery ran away as fast as it could and never came out. Today, before feeding, I looked for the mystery, and found it hiding below a rock, looking super nervous. When I fed, I could see it wanted to come out for food, but dare not. My tank is too crowded to get either the mystery or six line out. At this rate, I think the mystery will be dead in a couple more days . I know six line can be aggressive, but I also know mystery is not easy either. Given the mystery is almost twice as large as the six line, I would never expect it to be so scared of the six line like it's seeing ghost, especially after they live together perfectly peacefully for the last two years. Has anyone experienced anything like this before?