You don’t normally see anemonefishes stacked this densely, but the exception seems to be with the melanopus group. These species are almost exclusively found in Bubbletip Anemones (Entacmaea quadricolor), and, since their host often appears in huge colonies, so do they.
This video, which was filmed in Guam, is particularly interesting in that it illustrates how peaceful these anemonefishes can be towards one another in the wild. There is relatively little squabbling going on, perhaps because there are just so many damn anemones, but this is in stark contrast to how aggessive this group’s members are in captivity.
This is, of course, the same group that contains the Tomato Anemonefish (A. frenatus), one of the most singularly mean marine creatures I’ve ever had the displeasure to have met. If you’ve ever stuck your fingers anywhere near one of these awful beasts, you know what I mean. This is one fish which is never shy to attack, and, yet, the dozens of individuals seen in this clip are quite happy to go about their business. Hmm.