Each group of fish consists of a breeding pair and 0-4 non-breeders. Within each group there is a size-based hierarchy: the female is largest, the male is second largest, and the non-breeders get progressively smaller as the hierarchy is desceded. If the female dies, the male changes sex and becomes the breeding female, while the largest non-breeder becomes the breeding male (Ref. 47841). Also Ref. 7471.