ECOLOGICAL AND GENETIC DIFFERENTIATION OF BARBUS-CALLENSIS POPULATIONS IN TUNISIA

Enzyme electrophoresis on horizontal starch gel was carried out on 356 barbel individuals. The sampling comprised 278 individuals of the spe cies Barbus calensis from 10 rivers in Tunisia. The other individuals belonged to reference species (outgroups) from France and Morocco. An ecological study was also carried out on Tunisian rivers. The results show a clear differentiation of the two samples from northwestern Tuni sia, which was only partly correlated with ecological characteristics of the rivers they inhabit. There is no genetic dine, but rather a dis continuity between populations in the northwestern-most watershed and all the other Tunisian populations. This differentiation probably has a paleohistoric origin not only related to adaptation to ecological co nditions but also to difficulties in colonizing the watersheds. The re sults do nor indicate clearly a colonization direction for the genus B arbus in North Africa. Analysis of the Algerian populations would appe ar to be indispensable. Lastly, in contrast with the usual taxonomy, M orocco and Tunisia are populated by two closely related species, but B . callensis should remain the name of the Tunisian species, which was the first to be described in the small Kebir basin, a river that flows from Tunisia to Algeria. (C) 1995 The Fisheries Society of the Britis h Isles