The fish diversity of the river systems of the Kahuzi Biega National Park (East DRC)
The fish diversity of the Lowa and Ulindi systems, both right bank tributaries of the Upper Congo (Lualaba), has been underexplored and poorly known. As a result, the diversity and distribution of the fish species of these systems remained almost terra incognita. These two systems drain the Kahuzi-Biega National Park (KBNP). The absence of scientific fish collections from this park hinders the integration of the fish fauna from the park into the conservation plans. The present work is intended to fill existing gaps in the knowledge of the fish diversity and distribution, not only at the level of the two basins but also, and more specifically, at the level of the KBNP. At the same time, some taxonomic problems have been addressed through morphological and/or molecular approach(es).
The fish diversity of the Lowa Basin is composed of 119 valid species, 21 species from the Ulindi basin and seven from some affluents of Lake Kivu. Seven new species were discovered of which two are formally described and five remaining await description. For the KBNP as a whole, our endeavors enable the compilation of a list of 52 valid species from the Lowa basin, but Clarias licocephalus was sampled in the park, in the Lwiro, an affluent of Lake Kivu, and Amphilius kivuensis was observed from the source of the Luka. The two new species described herein are Marcusenius kaninginii, a species with eight circumpenduncular scales and Enteromius sp. 'radari', a species with a weakly ossified and serrated dorsal spine. In two case-studies we found traces of a complex evolutionary history, with hybridization events at the origin of speciation. (i) Enteromius sp. 'radari', a new species from the Lowa, shares morphological characters with two populations from the Sakasao and Bisuli affluents of the Luka River. Both populations form a separate mtCOI lineage, basal to a large lineage to which multiple genetic groups of E. miolepis, such as those from the Lowa basin, belong. (ii) An integrative approach using morphological and molecular data (Cytb and COI), was carried out on extensive samples of four species and their relatives: L. longifilis with a mental lobe, L. paucisquamatus with a small mental lobe, L. brauni and L. longidorsalis both lack a mental lobe but have a cornified cutting edge on the lower jaw. Divergent results were observed on the molecular level. Both species with a cornified cutting edge belong to different evolutionary lineages. Labeobarbus brauni is regarded as member of the lineage of Lab.-mouth species, although its distinct mouth phenotype. Furthermore, L. upembensis from Upper Lualaba with a cornified cutting edge belongs to the same lineage. The observed topology of L. paucisquamatus on the mitochondrial loci confirms, at present, the hybrid origin of the species. Labeobarbus longifilis and L. brauni are so far known as the parental species. Interestingly, a slight ecological habitat segregation is observed between L. paucisquamatus and both its putative parental species. The same holds true for the two Labeobarbus species with a cornified cutting edge on the lower jaw. The Lowa basin, is likely a basin where complex evolutionary events have occurred, probably, because the investigated stretch of the basin is highly isolated by waterfalls and rapids which might have facilitated the observed phenomena.
Our results will hopefully motivate DRC’ stakeholders of conservation to better incorporate entire watersheds in conservation strategies, by including affluents of the Middle Luhohowithin the protected area, which contain a number of endemic species, while all being situated outside the borders of the park.