Some species of cichlid form groups with younger fish looking after babies. Often these fish are unrelated to the larger , more dominant fish.
Cooperative breeding of this kind has puzzled evolutionary biologists for a long time as it is costly and often does not generate obvious fitness benefits to subordinates. In the case of Neolamprologus. pulcher, the main benefit for subordinates to stay in a territory of dominant breeders seems to be the protection gained against predators provided by the large group members.
This study shows a direct relationship between the relatedness of these helper fish to the offspring and the amount of care they provide.