Ecology and breeding behavior of a cichlid fish, Cyrtocara eucinostomus, on a large lek in Lake Malawi, Africa

Cyrtocara eucinostomus, a mouthbrooding cichlid, breeds on a 4 km long breeding arena between 3–9 m depth in the Cape Maclear region of Lake Malawi. At times over 50,000 males display there, making this breeding arena the largest ever reported. The form and function of the arena and the behavior of the fish on the arena are analogous to bird leks. This arena serves only as a mating ground. All parental care is provided by the females, which leave the arena with the eggs. Courtship takes place in the morning and most of the males leave in the afternoon to forage on zooplankton in deeper water. They return at dusk. The few males that remain on the arena switch their behavior from courting to foraging on zooplankton. Comparisons of this fish arena are made with bird leks and it is concluded that the mating system of this fish can be defined as a lek in the avian sense. 1) There is no male parental care and an absence of monogamous pair bonding. 2) Males and females are sexually dimorphic and there are males present which mimic females to gain entrance into the arena. 3) The arena is traditional with a lack of environmental constraints and is away from the primary feeding grounds. In order to determine 1) if this arena could be considered a true lek and 2) what the factors are which account for the location of this remarkably large arena in shallow water, data were collected upon: 1) the depth distribution of C. eucinostomus; 2) distribution and size of the nests on the arena; 3) the behavior of the fish on the arena; 4) the feeding habits of C. eucinostomus; 5) the distribution of the zooplankton upon which C. eucinostomus feeds; 6) water temperature throughout the year; 7) response of males to cormorants; 8) depth distribution and stomach analysis of predatory catfish which feed on C. eucinostomus. Based on this natural history data, it is concluded that the occurrence of the arena in shallow water is probably due to C. eucinostomus avoiding deep dwelling catfish which feed at night upon them and other cichlids.