Spawning of large Barbus (Barbus intermedins Complex) in a small river of the Lake Tana basin (Ethiopia) and relationships of some putative species

Abstract

Direct observations on three forms (morph types) of spawning barbs, considered by some authors as different species, were carried out in September–October 2005 at the Gumara River and its small tributary, the Ducalit, in the Lake Tana basin. The spawning barbs were sampled using cast nets. Barbs of different morphotypes composed common spawning aggregations and were caught together. It is likely that troutlike females mate extensively with intermedius males and, probably, with bigmouth small-eye males. Experiments in artificial fertilization and rearing showed that, during the embryonic period, there was no increase in mortality of progeny from crosses of barbs of different morphotypes, in comparison with homonomic crosses, thus suggesting an absence of postzygotic reproductive isolation between the morphotypes. At the same time, mortality of progeny from crossing barbs with Varicorhinus beso Ruppell, 1836 was very high during the earliest stages of development, suggesting strong, even if incomplete, reproductive isolation ensured by postzygotic mechanisms.