AbstractSchilbe mystus(L.) andEutropius niloticus(Ruppel) (fm. Schilbeidae) from rivers of the Volta Basin were screened at 18 enzyme loci for electrophoretically detectable variation. The mean observed heterozygosity was 0.001 inS. mystusand 0.018 inE. niloticus. The possible causes of these rather low levels of genetic variation are considered in relation to natural and human influences in the Volta Basin river system. The results also suggest that the speciesS. mystusconsists of several distinct biological species and thatE. niloticusmay have evolved from within theSchilbegroup.