Gracing our AquaNerd Picture of the Week this time around is a very common fish in the trade, the Blue Green Reef Chromis (Chromis viridis). These beautifully iridescent fish are often bought in small groups and they tend to play well together in large reef tanks. The blue green chromis is quite hardy, and they are great fish for beginners, but they do have a bit of a nasty side. In small tanks, a shoal of these fish can quickly become one or two individuals as aggression within the group takes over and the dominant individuals kills the others. This is a trait common to most schooling fish when placed in captivity, and given the relation between chromis and damselfish, it’s expected with this species.