Not all social coral reef fishes form strict size-based dominance hierarchies: An investigation of intraspecific size ratios in Dascyllus aruanus.

We present a random pattern of body size ratios between adjacent ranked group members in the humbug damselfish Dascyllus aruanus. This random distribution of size ratios differs from the other well-known group-living coral reef fishes which exhibit non-random, well-defined and closely regulated size differences between ranks. Our results suggest a relaxation of social constraints in D. aruanus which may be due to its social system, mating system, capacity for movement or a combination thereof. Investigating how these traits co-vary within and among populations is an interesting avenue of future research.