Lacustrine spawning: is this a new reproductive strategy among ‘large’ African cyprinid fishes?

Changes in the gonado‐somatic index and abundance of the different Labeobarbus species in the mouths of four major afferent rivers of Lake Tana, Ethiopia, were monitored monthly during 1999 and 2000. Riverine spawning was characteristic for seven of Lake Tana's 15 contemporary Labeobarbus species. These seven did not show spatial segregation among afferent rivers but significant temporal segregation occurred in aggregating in the river mouths and migrating towards the upstream spawning areas during the breeding season (June–October). Among the eight other species, peak gonad development occurred generally in the same period as in the riverine spawners. These species, however, did not aggregate in the river mouths during the breeding period and were absent from the upstream spawning areas. A derived, novel strategy, lacustrine spawning was hypothesized for these eight Labeobarbus species. This hypothesis was further supported by observations of running female fishes in the littoral zones distant from any of the afferent rivers. This derived strategy is only common among the littoral‐dwelling Labeobarbus species with restricted distribution patterns. At present it is thought that sequential waves of speciation and habitat divergence followed by trophic specialization, shaped the diversity of Lake Tana labeobarbs.