The utilization of microhabitats, mating systems and parental care of 12 cohabiting cichlid fishes in the tribe Lamprologini were investigated at Pemba on the northwest side of Lake Tanganyika for 2 years. From differences in the number of females with whom one male simultaneously mated and the male's contribution to parental care, these fishes were
categorized into temporarily haremic species (Altolamprologus compressiceps, Lamprologus Jemairii, Neolamprologus Isscistus, and Lepidiolamprologus profundico/a), permanently haremic species (Neo/amprologus furcifer, N. modestus, and N. savory,) and mono/bigamous species (Lepidiolamprologus attenuatus, L e/ongatus, Neolamprologus
tose, N. tretocephslus, and N. brichard1). Successive removal experiments of a pair and its brood at 59 sites for 2-12 months demonstrated that each species has a specific selectivity of breeding sites. The egg size and reproductive output of temporarily haremic species, which corresponded to "hole brooders· using rock holes, were large and their sexual dimorphism in size was great compared to the other species. I suggested that the selectivity of breeding sites of each species has profoundly influenced the evolution of its reproductive characteristics, mating system and parental care. The mechanism of coexistence was discussed from the viewpoint of partitioning of breeding sites among the species.