I've had a dragon goby for about 2 years now and it's grown to about 9" and bigger around than a quarter. I just bought another dragon goby (6" and nearly as big around as a penny, still pretty thin) about 3 weeks ago and have kept it in quarantine since. I just tried introducing the new goby into the tank with the larger goby and the larger goby tried to bite the smaller goby. I've always been under the impression that these fish will get along with their own kind. Will these fish ever get along or will they always fight? If they will get along, how should I introduce the smaller goby to prevent the larger one from attacking?