The reproductive biology of an open-water spawning Lake Malawi cichlid, Copadichromis chrysonotus
Copadichromis chrysonotus is a zooplanktivorous cichlid member of the diverse fish community inhabiting Lake Malawi’s rocky, littoral habitat. Like most Lake Malawi cichlids, this species’ reproductive strategy is based on maternal mouthbrooding, but it is the only littoral species known to spawn in the open water without a substrate-based territory. This study investigated length at maturity, sexual dimorphism, spawning behaviour, breeding seasonality, fecundity, fertility, egg size, and brooding habits of C. chrysonotus in southern Lake Malawi. Males in breeding colouration aggregated in sheltered areas at least several metres deep, and each male defended a mobile breeding territory near the surface while attempting to attract females. Breeding was mostly continuous from August to May, with peaks in August–September and January–March. A major lull in breeding activity occurred in May and June. Mean fecundity and fertility increased significantly with female total length, while mean egg length, mean egg mass and gonadosomatic index did not increase significantly with female total length. Females brooded their young up to 15–16 mm total length before abandoning them. Open-water spawning by C. chrysonotus may be an adaptation to reduce both egg predation during spawning and competition for substrate-based breeding territories.
Key words: breeding, dimorphism, fecundity, fertility, gonadosomatic index, maturity,
mouthbrooding, spawning, territoriality.