A new mastacembelid species from Lake Tanganyika: a case of complex evolutionary history.

A detailed morphometric study of 123 specimens identified as Mastacembelus albomaculatus and the six syntypes of M. tanganicae was undertaken. On each specimen, 27 morphometric measurements and 12 meristics were taken. The type series of M. tanganicae contains more than one species, with four specimens attributed to a new species M. reygeli sp. nov. A redescription of M. albomaculatus and a description of the new species are provided. Both species are endemic to the northern and central part of Lake Tanganyika. They can be distinguished based on the number of caudal vertebrae [47-52 (median 49) in M. albomaculatus v. 42-46 (44) in M. reygeli sp. nov.], the total number of vertebrae [85-90 (88) v. 78-83 (81)] and the distance from the snout to the last externally visible dorsal spine (S-LDS) [61.8-67.0 (mean 64.0) v. 66.6-71.5 (68.6)% L(S)]. In addition, intermediate specimens and populations between M. albomaculatus and M. reygeli were discovered from several parts of the lake, but mainly from the southern part. The latter intermediate populations were provisionally identified as introgressed populations.