2.2. Natural geographical distribution
Although more than 100 different species of the Genus Clarias have been described in Africa, a recent systematic revision based on morphological, anatomical and biographical studies has been carried out by Teugels (1982a, 1982b, 1984), who recognized 32 valid species. The large African species which are of interest for aquaculture belong to the subgenus Clarias. In earlier systematic studies on the large African catfish species Boulenger (1911) as well as David (1935) recognized five species within this subgenus. Both authors used morphological criteria such as form of vomerine teeth, ratio of vomerine to premaxillary teeth band and the number of gill rakers. The five species were:
· Clarias anguillarusIn 1982 Teugels revised the subgenus Clarias and found only two species (C. gariepinus and C. anguillaris) if the number of gill rakers on the first branchial arch was considered; for C. anguillaris the number of gill rakers was rather low (14 to 40) while for C. gariepinus relatively high (20 to 100, Figure 1).
· Clarias senegalensis
· Clarias lazera
· Clarias mossambicus
· Clarias gariepinus
Figure 1. Regression lines showing the correlation between standard length and number of gill rakers on the first branchial arch of the catfish species of the subgenus Clarias recognized by Boulenger (1911) and David (1935). Source: Teugels, 1982b.
Clarias gariepinus, which is generally considered to be one of the most important tropical catfish species for aquaculture, has an almost Pan-African distribution, ranging from the Nile to West Africa and from Algeria to Southern Africa. They also occur in Asia Minor (Israel, Syria and South of Turkey). By contrast, Clarias anguillaris has a more restricted distribution and is found in Mauritania, in most West African basins and in the Nile (Figure 2). In general C. gariepinus lives in most river basins sympatrically with C. anguillaris.
Figure 2. Geographical distribution of the African catfish.