I had a brown one living in my overflow along with a blue flasher wrasse for over 4 months. They got along just fine. The green ones do eat fish though so stay away from those. I am not saying the brown ones cant or dont just mine didnt. They are opportunistic and I am sure if tempted and or hungry enough will eat a small fish. The Brown one I have is big too, legs are over 8" and body is bigger then a quarter. I used to see two or three legs sticking out over the top of the overflow catching food and dragging down into the overflow (guess it couldnt wait for it to come to him). Kinda creepy.