Societies of the shell-dwelling cichlid Neolamprologus multifasciatus

The cichlid Neolamprologus multifasciatus is among the smallest fish in Lake Tanganyika but can dominate areas of the lake floor, living in stable territorial groups with clear memberships that persist for years. This fish is found on ‘shell bed’ habitats, regions where vast numbers of empty snail shells have accumulated over millennia, preserved by the lake’s alkaline waters. Group members take shelter inside the shells that they dig up from the lake floor, aggregating them within their territories with each defending its own shell fiercely, even against much larger rivals, while jointly defending the overall group territory from outsiders. Although miniscule in stature, this fish displays a rich, complex social life in which conflict and cooperation play out against the backdrop of extreme population densities, predation threats, resource defence and ingroup/outgroup interactions. The presence of these fish also imprints itself on the landscape, where their excavation efforts create a cratered, almost lunar landscape on the lake floor, the result of society level territoriality. In the ancient waters of this Lake, these fish are furious with activity, constantly tending to their shelters and engaging in social interactions comparable to the complexity and subtlety of many societies in larger taxa. • The ‘multi’ cichlid lives in stable territorial groups (of up to 20) that persist for years. • Groups typically include a dominant male, adult females, juveniles and subordinate males. • Each group member resides in its own ‘home shell’ that they dig up from the lake floor. • Individuals defend their own shell fiercely but jointly defend the group’s territory. • Constrained dispersal and territorial inheritance likely support group stability.