I would like to discuss a peculiar type of hermaphroditism, which has been discovered in the ‘Mbuna’. The Mbuna are a group of cichlid fishes endemic to Lake Malawi. They are unique in various aspects of taxonomy, so that Fryer (1959), who made a fundamental ecological study of them, proposed to grant them the rank of a tribus. The Mbuna are small fish living around the shore of the lake, mostly in shallow water. The different species are in a fascinating way adapted to the many special niches within the great diversity of ecological conditions along the rocky and sandy seashore, where they live in extremely dense populations. Some Mbuna species have been introduced as aquarium fish, because of their beautiful coloration and their interesting mode of reproduction; all the females being mouth-brooders.