Strange things happen in Lake Malawi, in central Africa. The waters teem with many species of cichlid fish, whose mysterious courtship rituals baffle zoologists.
In some types of cichlid, each male builds a bower or egg-mound in the sand, which he hopes will so impress a female that she will lay her eggs above it. These bowers vary in height from about 1.5 in (40 mm) to 6 in (15 cm) or more, some being splendid 'sandcastles' 10 ft (3 m) across. Yet others may be crater-shaped, flat-topped or just a scrape in the sand.
Males of the same species build their bowers close together in one of the areas where courtship displays take place. This enables interested females to inspect all the bowers and select a mate.
What makes a female cichlid choose one male above all others, is still a mystery. There is no discernible pattern of behaviour, and what determines a male's success remains unknown.