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Fish have been widely translocated into non-native areas, commonly as fishery targets. Since fish figure as hosts of various parasite taxa, their introduction may pose often-underestimated threats to ecosystems. However, parasites can also serve to track host species’ introduction routes when these would otherwise be unknown. To verify the potential of parasites in reconstructing invasion routes, we investigated two of the best-documented introductions: those of Limnothrissa miodon into lakes Kivu and Kariba. As a proof of concept, we investigate the possibility of using parasites to evaluate the effect of host size in the introduction pathway and to track the host origins of L. miodon. Combining historical collections and recent field samples, specimens of L. miodon from Lake Kivu and Lake Kariba were examined for monogenean flatworms. Intraspecific variation was investigated using morphometrics of the parasite’s sclerotised structures. Three markers from the ribosomal DNA region were used for genetic parasite identification. In Lake Tanganyika, L. miodon is infected by two species of monogeneans, Kapentagyrus limnotrissae and K. tanganicanus. One of these species, K. limnotrissae, was found on L. miodon from Lake Kariba. In contrast, not a single monogenean individual was found in specimens from Lake Kivu. Morphometric results suggested that the origin of K. limnotrissae introduced into Lake Kariba may be the southern part of Lake Tanganyika, which corresponds to historical reports. Moreover, differences in the size of introduced fish, fry versus juveniles, were proposed as one of the factors influencing parasite occurrence in non-native areas. This supports the potential use of monogeneans as markers for host origin. This study was supported by ECIP (European Centre of Ichthyoparasitology); project No. P505/12/G112. Work in the collections of RMCA (Royal Museum for Central Africa) was financed by the SYNTHESYS Project (http://www.synthesys.info/) (BE-TAF-5731) which is financed by European Community Research Infrastructure Action under the FP7 Integrating Activities Programme.

Lake Tanganyika is the deepest and oldest African Great Lake and of economic importance. While the diversity of its endemic cichlid radiations yielded scientific interest, a number of cichlid tribes have few representatives in the lake. Some of those, namely Oreochromini (ex-Tilapiini), Haplochromini and Tylochromini, reach higher species numbers in riverine systems. Conversely, the phylogenetic position of the monospecific and endemic Boulengerochromini is unclear. The oreochromines Oreochromis tanganicae and Oreochromis niloticus, the haplochromine Astatotilapia burtoni, the tylochromine Tylochromis polylepis and the boulengerochromine Boulengerochromis microlepis, the largest cichlid species worldwide, were surveyed for ancyrocephalid monogenean gill parasites. Five new species are proposed. Cichlidogyrus gillardinae sp. n. is described from A. burtoni, Cichlidogyrus mbirizei sp. n. from O. tanganicae and Cichlidogyrus nshomboi sp. n. from B. microlepis. T. polylepis harbours Cichlidogyrus mulimbwai sp. n., Cichlidogyrus muzumanii sp. n. and a third, presently undescribed species. Four species known from outside the Tanganyika Basin were retrieved on the oreochromines. The host species are scientific models or important in the sectors of fisheries or ornamental fish trade. Moreover, their phylogenetic positions render them well-suited to help elucidate the historic relationships between riverine and lacustrine African cichlids. In this framework, their Cichlidogyrus fauna is compared to congeners known from African rivers and to the few Tanganyika representatives described. While the parasites of Oreochromis, A. burtoni and T. polylepis are reminiscent of those infecting related hosts throughout Africa, B. microlepis hosts a Cichlidogyrus morphotype typical of Lake Tanganyika. This supports its placement within an endemic cichlid radiation.