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@font-face { font-family: "Cambria";}p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman"; }div.Section1 { page: Section1; }The cichlid flocks of the EastAfrican Great Lakes are the most diverse vertebrate radiations on earth andthey form an ideal model system for studies on speciation and diversification.Lake Tanganyika is the oldest and deepest lake in the East African Rift and itscichlid assemblage seeded all radiations in the other Great Lakes. Many cichlidtaxa harbour different colour morphs. Yet, at least for Lake Tanganyika, themost spectacular example hereof is provided by Tropheus. Tropheuscontains over a 100 often profoundly different colour morphs that are mostlyfound in allopatry. Many of these varieties have complex distribution patternsthat can sometimes be explained by lake level fluctuations. Although Tropheus species are popular in theaquarium trade and established model organisms in evolutionary research, theirtaxonomy was confusing. Hence, it was often not possible to identify most ofthe colour varieties to the species level. In this dissertation, Tropheus is revised. Seven species areidentified, three of which are new to science. For two species, previouslystated synonymies are confirmed. The distribution patterns of Tropheus species are linked to thelake’s three subbasins. These were once separate basins and Tropheus underwent a differentevolutionary history in each of them. It had been suggested that differentTropheus populations could hardly bedistinguished on morphological grounds. Different case studies presented hereshowed substantial morphological differentiation in the genus. Yet,intra-specific differences between populations sometimes surpassedinter-specific differences. Hence, we verified which criteria should be used todistinguish species in Tropheus. Acomparative study showed that body proportions were of less use in this respectthan were meristics. Finally, Simochromis and Pseudosimochromis,two genera related to Tropheus wererevised as well. For this we did not only focus on fish morphology but also on Cichlidogyrus gill parasites. Giventheir high host-specificity, these can be used as additional markers in speciesrecognition. In this study, six parasite species were described. Four hostspecies were transferred from Simochromisto Pseudosimochromis and onesynonymy was established.