We analysed the genetic differentiation among 17 natural populations of the Nile tilapia Oreochromis niloticus (Linnaeus, 1758) using allozymes and restriction fragment length polymorphism (RFLP) of mitochondrial DNA (mtDNA). The populations studied, from the River Senegal to Lake Tana and from Lake Manzalla to Lake Baringo, represent all subspecies which have been previously described. Sixteen variable nuclear loci showed that these populations can be clustered in three groups: (1) West African populations (Senegal, Niger, Volta and Chad drainages), (2) Ethiopian Rift Valley populations (Lakes Awasa, Ziway, Koka and the Awash River) and (3) Nile drainage (Manzalla, Cairo, Lake Edward) and Kenyan Rift Valley populations (Lakes Turkana, Baringo and River Suguta). Nine different mtDNA haplotypes were found in the RFLP analysis of a 1 kb portion of the D-loop region. The network obtained showed that there are three geographically distinct groups; all West African populations and 0. aureus are clustered, the two Ethiopian Rift Valley populations are distinct and between these two groups are the Kenyan and Ugandan Rift Valley populations. Nile populations show affinities both with West African populations and with specimens from Lakes Tana and Turkana. Taxonomic and biogeographical implications of these results are discussed.

We analysed the genetic differentiation among 17 natural populations of the Nile tilapia Oreochromis niloticus (Linnaeus, 1758) using allozymes and restriction fragment length polymorphism (RFLP) of mitochondrial DNA (mtDNA). The populations studied, from the River Senegal to Lake Tana and from Lake Manzalla to Lake Baringo, represent all subspecies which have been previously described. Sixteen variable nuclear loci showed that these populations can be clustered in three groups: (1) West African populations (Senegal, Niger, Volta and Chad drainages), (2) Ethiopian Rift Valley populations (Lakes Awasa, Ziway, Koka and the Awash River) and (3) Nile drainage (Manzalla, Cairo, Lake Edward) and Kenyan Rift Valley populations (Lakes Turkana, Baringo and River Suguta). Nine different mtDNA haplotypes were found in the RFLP analysis of a 1 kb portion of the D-loop region. The network obtained showed that there are three geographically distinct groups; all West African populations and 0. aureus are clustered, the two Ethiopian Rift Valley populations are distinct and between these two groups are the Kenyan and Ugandan Rift Valley populations. Nile populations show affinities both with West African populations and with specimens from Lakes Tana and Turkana. Taxonomic and biogeographical implications of these results are discussed.

Genetic variation of the Oreochromis esculentus population from Lake Kanyaboli was studied using 24 allozyme loci and three microsatellite loci and compared with four populations of O. niloticus. Results strongly suggest that this population can be considered as pure. 1999 The Fisheries Society of the British Isles

No abstract

Eleven samples of Chrysichthys nigrodigitatus and one sample of C. maurus were studied using morphometrics and enzyme polymorphism. Samples from opposite areas in the range of the species were most differentiated morphologically (Dagana in Senegal and Selingue in Mali, on one hand, and Bas Kouilou in Congo, on the other hand). In the sample from Bas Kouilou, most specimens overlap those from Ebrie Lagoon in C6te d'Ivoire. The populations from C6te d7Ivoire are genetically the mo'st variable and have the highest number of alleles in common with the sample of C. maurus (ancestral alleles). The samples from the limits of the species' range (Dagana, Bas Kouilou) are those that have the least polymorphism (both monomo@hs) and the fewest alleles in common with C. maurus. On the basis of these results we present a hypothetical scenario for the colonization of basins by populations of C. nigrodigitatus after the last glaciation. Colonization started in the area between C6te d'Ivoire and Benin. From this region of origin, some populations colonized the basins to the west via the coastal area up to Senegal. Independently, other populations colonized the basins to the east via the coastal area up to Zai're. The colonization of the Niger most likely occurred through its Lower Delta.