Yeah it is fish only for the most part. I put a couple zoas, green star, and a war coral in there as well. As far as why they did not make the cut. I already have two bar gobies in there, the fire fish were bullied by my bristle tooth, and the lunar loves to eat shrimp. The grouper, diadema, scooter blenny and cardinal were all in a 20 gallon that I transfered to the 55 because I didnt want to setup a third tank.