My new green terror has been in his 55 for a few weeks now and I couldn't get him to come out of his cave for the life of me. I had a comet goldfish then I bred for my oscars that managed to live and get big. So since he was never a desired fish I put him in with my gt as a target fish. It worked perfect, my gt hangs out with him all day now so for no agression that I can see but now he's out cruising the tank all the time. The gold fish just isn't allowed in the cave.