Most of the information on growth for African cichlid fishes refers to members of the genus Tilapia, the most important commercially, but which represents only a small part of the adaptive range coveredby the family as a whole. Species of the genus Haplochromis are endemic to Lake Nyasa; they feed on zooplankton, and some have a well-defined breeding season. An analysis of suitable length-frequency data allowed a comparison of growth parameters with those of other species of cichlids which indicates that, although these fish are comparatively small, they do not reach maturity until their third year; as they have a high relative growth rate, they become adult late in their growth history. The data for one of the species of Nyasan zooplankton-feeding Haplochromis, H. virginalis, indicate that the adult part of the population leaves the inshore feeding area some time before the spawning period and returns later to breed. This is seen as a stage in the process by which the open waters of the lake are colonized; a second species in the same group appears to spend the whole of the year preceding first breeding in the open lake, returning to inshore waters to breed each year. Both these species are widespread and abundant, and a link between their migratory habits (rarely found in other Nyasan cichlids) and the ecological success represented by this abundance is suggested, one that can be applied to certain species of Tilapia in the same lake. It is also suggested that this migration relieves competition amongst the more sedentary species which share the same zooplankton food resource.