The breeding biology and early development of the common southern African clariid catfish, Clarias gariepinus (Burchell), are described. C. gariepinus reaches maturity towards the end of the second year (350 mm TL, rarely towards the end of the first year, 240 mm TL). The modal size of breeding fishes is 540 mm in females and 580 mm in males. A modal size female produces about 50,000 eggs, but large females may produce over 150,000 eggs. Gonadal maturation stages are described. Gonadal maturation is associated with increasing water temperatures and photoperiod from July to September, and the spawning season extends from September to March (Summer). Spawning takes place at night, usually after heavy rain in recently inundated marginal areas. There is a massive aggregation of catfish before spawning, and courtship is preceded by aggressive encounters between males. Mating takes place between isolated pairs in shallow water among inundated terrestrial or semi-aquatic grasses and sedges.
There is no parental protection of the young (as found in many other catfish families) except by the careful choice of a suitable spawning site. Egg and larval development is rapid and the larvae are capable of swimming strongly within 48 hours of fertilization. The larvae are secretive and feed on small invertebrates which are abundant in the shallow inshore areas which they inhabit.
As C. gariepinus awaits suitable environmental conditions for spawning, this species is far more dependent on external factors, especially rainfall and water level, than two cichlids, a guarder and a mouth-brooder, which also occur in Lake Sibaya.
The breeding biology of other species of Clarias (mainly in the subgenus Clarias (Clarias)) is reviewed and compared with that of C. gariepinus. The marked dichotomy between nest-guarding in two Asian species, and non-guarding, open-substrate spawning in all other Asian and African species, is noted. Finally, further interesting lines of research on the breeding biology of Clarias species are outlined.