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Pelagic zones are characterised by consistent large-scale patterns of circulation on local and global scales. Lake Tanganyika, as an enclosed ecosystem provides a playing field to study evolutionary and ecological processes applicable to open water areas worldwide. Despite their important role in the ecosystem, large scale patterns of the distribution of parasites remain poorly understood. Monogenean parasites have been proposed as tags for ecosystem dynamics because of their direct life cycle and often high host specificity. We combined data on spatiotemporal dynamics of parasites (Kapentagyrus, Monogenea) with morphological variation of clupeid hosts to investigate general patterns of host-parasite interactions in the pelagic zone of this ancient lake.Two dominant species of clupeid fishes in the pelagic zone of Lake Tanganyika are parasitised by two monogenean species ofKapentagyruswith different levels of host specificity. The host fishes are believed to perform lake-wide migrations driven by seasonal upwellings. To model spatiotemporal dynamics of host-parasite interaction, we used temporal data on monogenean infection along the North-South axis of Lake Tanganyika based on 1730 screened fishes and 3710 parasites together with phenotypic characterisation of the clupeid hosts.Infection levels are dependent on host body size with contrasting trends in the two parasite species. We reveal temporal stability of infection with spatial distribution restricted by host life strategies. Spatial differences between the parasite species most likely reflect differences in migration between the host species; these are also reflected by morphological differences between some clupeid populations. Our results also suggest mutual facilitation of infection.In conclusion, parasite infection is geographically restricted by host life strategies even in this ecosystem lacking physical barriers. Intensity of infection seems to be mainly driven by host size, with so far rarely reported mutual facilitation of coinfection. Temporal stability of infection in the pelagic zone contrasts with seasonal changes in abundance of clupeid hosts. Overall, our results suggest that parasite infection dynamics in the open water areas are dependent on life style and not host density.

African Great Lakes and their fauna are among the prime model systems for evolutionary research. Lake Tanganyika is the second deepest lake in the world and its permanently stratified, relatively species-poor and well-delimited pelagic zone offers a simple model for ecosystem dynamics of open water areas worldwide. In our study, we focused on mitogenomic differentiation of directly transmitted parasites (Monogenea, Kapentagyrus) infecting two species of pelagic clupeid fishes across two subbasins of Lake Tanganyika, to unravel patterns of migration and population dynamics in the pelagic zone of large water bodies. Starting from pooled population samples, altogether containing more than 800 specimens, we provide the first population-genomic study on any parasite in the African Great Lakes. Our results indicate a lack of spatial population structuring in Kapentagyrus tanganicanus infecting its two clupeid hosts. In Kapentagyrus limnotrissae, a parasite specific to only one of the two clupeid hosts, spatial and seasonal restriction in gene flow are observed. Contrasting patterns in spatial population structuring between K. tanganicanus and K. limnotrissae reflect their differences in host range and in the life histories, migration and habitat preference of their respective hosts. This is a proof-of-concept of how parasites can be reliable tags for hardly traceable hosts, in this case indicating host and parasite connectivity throughout the hosts’ spatial distribution. Comparison of population-genetic parameters based on individual specimens versus pooled samples proofs PoolSeq as a suitable method in (mito)genomics of minute taxa that are hard to access in the field.

During colonial times, Nile tilapia Oreochromis niloticus (Linnaeus, 1758) was introduced into non-native parts of the Congo Basin (Democratic Republic of the Congo, DRC) for the first time. Currently, it is the most farmed cichlid in the DRC, and is present throughout the Congo Basin. Although Nile tilapia has been reported as an invasive species, documentation of historical introductions into this basin and its consequences are scant. Here, we study the genetic consequences of these introductions by genotyping 213 Nile tilapia from native and introduced regions, focusing on the Congo Basin. Additionally, 48 specimens from 16 other tilapia species were included to test for hybridization. Using RAD sequencing (27,611 single nucleotide polymorphisms), we discovered genetic admixture with other tilapia species in several morphologically identified Nile tilapia from the Congo Basin, reflecting their ability to interbreed and the potential threat they pose to the genetic integrity of native tilapias. Nile tilapia populations from the Upper Congo and those from the Middle-Lower Congo are strongly differentiated. The former show genetic similarity to Nile tilapia from the White Nile, while specimens from the Benue Basin and Lake Kariba are similar to Nile tilapia from the Middle-Lower Congo, suggesting independent introductions using different sources. We conclude that the presence of Nile tilapia in the Congo Basin results from independent introductions, reflecting the dynamic aquaculture history, and that their introduction probably leads to genetic interactions with native tilapias, which could lower their fitness. We therefore urge avoiding further introductions of Nile tilapia in non-native regions and to use native tilapias in future aquaculture efforts.

This study highlights the value of museum collections in invasion biology. It focuses on introduced tilapias, Oreochromis niloticus and Coptodon rendalli in the Congo Basin and their monogenean (Platyhelminthes) gill parasite fauna. O. niloticus was introduced throughout the Congo Basin while C. rendalli was introduced into the Lower Congo, but is native to the Middle and Upper Congo. In order to study the impact of these stocking events on the native parasite community we investigate the co-introduction and host switching of their parasites. Post-introduction material is compared with pre-introduction samples from museum collections of 5 native tilapias in the Congo Basin. Nine of the known parasites of O. niloticus were co-introduced, while one, Cichlidogyrus rognoni, is missing and possibly not established. In contrast, no parasite species were found co-introduced with C. rendalli into the Lower Congo. The parasite fauna of Tilapia sparrmanii shared no species with O. niloticus. Oreochromis mweruensis shared five species with O. niloticus, but these were also found on the pre-introduction samples, and are considered native to both hosts. We report three putative host switches: Cichlidogyrus sclerosus and Cichlidogyrus tilapiae to Coptodon tholloni in the Lower Congo Basin and Gyrodactylus nyanzae to C. rendalli in the Upper Congo. ispartof: Biological Invasions vol:22 issue:9 pages:2825-2844 status: published

BackgroundMonogenean parasites have never been formally reported on fish from the Lufira basin. Then it is hypothesised that multiple monogenean species are to be recorded that are new to the region. This study aimed to record the gill monogenean parasite fauna of three cichlid fish species in the Upper Lufira basin by inventorying their diversity (species composition) and analysing their infection parameters (prevalence, mean intensity and abundance).MethodsOreochromis mweruensis, Coptodon rendalli, and Serranochromis macrocephalus were selected for the study, given their economic value and their abundance in the Upper Lufira basin. Monogeneans were isolated from the gills and stomach, mounted on glass slides with either Hoyer’s medium or ammonium picrate-glycerin for further identification under a stereomicroscope, based on morphological analysis of genital and haptoral hard parts. Indices of diversity and infections parameters were calculated.ResultsA total of thirteen gill monogenean parasite species (Cichlidogyrus dossoui, C. halli, C. karibae, C. mbirizei, C. papernastrema, C. quaestio, C. sclerosus, C. tiberianus, C. tilapiae, C. zambezensis, Scutogyrus gravivaginus, S. cf. bailloni and Gyrodactylus nyanzae) and one stomach monogenean (Enterogyrus malmbergi) were reported. A species richness of S= 10 for O. mweruensis, S= 6 for C. rendalli and S= 2 for S. macrocephalus were recorded. Five parasite species were reported to be common amongst O. mweruensis and C. rendalli. The most prevalent parasite species were C. halli (P= 80.9%) on O. mweruensis, C. dossoui (P= 92.9%) on C. rendalli and C. karibae and C. zambezensis (both of which P = 9.1%) on S. macrocephalus with a respective mean infection intensity of 7.9 on O. mweruensis, 9.8 on C. rendalli and 5 and 15, respectively, on S. macrocephalus. Results of this study reported new host ranges for five parasites species (C. quaestio, S. cf. bailloni, E. malmbergi on O. mweruensis, C. halli on C. rendalli and C. karibae on S. macrocephalus) as well as new geographical records for three of them (S. cf. bailloni, E. malmbergi, C. karibae).ConclusionsThis study highlights the richness of monogenean communities in the Upper Lufira basin and is a starting point for future helminthological studies, e.g. on the use of fish parasites as indicators of anthropogenic impacts.

This study represents the first exploration of the parasite fauna of cichlid fishes in the Mweru-Luapula subregion (Central Africa). Twelve species of cichlids and 14 species of Monogenea from three genera (Cichlidogyrus, Gyrodactylus and Scutogyrus) were collected. We present a first record of the gill parasite fauna of eight host species, Oreochromis mweruensis, Orthochromis sp. ‘Mambilima’, Sargochromis mellandi, Serranochromis angusticeps, S. stappersii, S. thumbergi and Tylochromis mylodon. The host range of 10 parasite species was expanded. The study further includes the description of Cichlidogyrus consobrini sp.n. from S. mellandi and Orthochromis sp. ‘Mambilima’. A new morphotype of C. halli is characterized and three species, C. papernastrema, C. quaestio and C. zambezensis are redescribed. Furthermore, the biodiversity and host-specificity of these parasites are compared with cichlid parasites from Lake Kariba and Cameroon. Two species, including C. consobrini sp.n. and a new morphotype of C. halli, are putative endemics. Additionally, the parasite fauna is highly similar in species composition to Lake Kariba, but in Bangweulu-Mweru the same parasite species are more host-specific, probably because of hydrogeographical differences between the two regions. This research was supported by the Belgian Federal Science Policy Office (BRAIN-be Pioneer Project BR/132/PI/TILAPIA), the University Development Cooperation of the Flemish Interuniversity Council (VLIR-UOS, South Initiative Renforcement des capacites locales pour une meilleure evaluation biologique des impacts miniers au Katanga (RDC) sur les poissons et leurs milieux aquatiques, ZRDC2014MP084) and the Mbisa Congo project, a framework agreement project of the RMCA with the Belgian Development Cooperation. M.P.M.V. was supported by a travel grant from the Research Foundation - Flanders (FWO-Vlaanderen) and Czech Science Foundation project no. P505/12/G112 (ECIP). Moise Katumbi Chapwe is cordially thanked for his kind hospitality and support. Also E. Abwe, B. Katemo Manda and C. Mukwene Mulele are cordially thanked for their help with the fish sampling, and W. Fannes, M. Kasongo Ilunga Kayaba and C. Kalombo Kabalika for their effort in parasite preparation. M. Barson, T. Dube and the technical team at the University of Zimbabwe Lake Kariba Research Station are thanked for delivering fresh gills of S. macrocephalus from Lake Kariba, Zimbabwe; J.-L. Justine (MNHN) and A.J. Phillips (Smithsonian) for the loan of type material; I. Přikrylová for sharing her expertise on Gyrodactylus; M. Van Steenberge for his valuable input regarding this ecoregion and its ichthyofauna; A. Henrard for his help with stacking images; G. Cael for his help with constructing fig. 1; and two anonymous referees for their valuable comments.

Nile tilapia, one of the most popular aquaculture species worldwide, has been introduced into the Congo Basin several times. In previous morphological studies, we showed that some of the monogenean gill parasites were co-introduced with Nile tilapia and some spilled over to native Congolese cichlids. In this study, we investigated the co-introduced monogeneans of Nile tilapia genetically from three major parts of the Congo Basin; Upper, Middle and Lower Congo. We generated sequences of Congolese native and introduced monogeneans from native and introduced tilapias and evaluate their position in a phylogeny. Additionally, we generated sequences of the same species of monogeneans co-introduced with Nile tilapia in Madagascar and of a native population of Nile tilapia from Burundi. Our results confirm the co-introductions in the Congo. We found that co-introduced parasites are less genetically diverse than native ones, and that there was no geographical pattern between introduced populations. Furthermore, our COI haplotype networks suggest multiple introduction events of Nile tilapia into the Congo Basin. Additionally, we tested the barcoding gap and the performance of mitochondrial COI and nuclear ribosomal ITS-1, 28S and 18S markers. We found a significant intra/interspecific barcoding gap of 15% for COI, but none for the other markers. Our molecular results reveal that Cichlidogyrus halli, C. papernastrema, C. tiberianus, C. cirratus and C. zambezensis are in need of taxonomic revision.

BackgroundMonogenea van Beneden, 1858 is a group of parasitic flatworms, commonly found infecting bony fish. Several genera, such asCichlidogyrusPaperna, 1960, are reported to include potential pathogenic species that can negatively impact aquaculture fish stocks. They can switch from introduced to native fish and vice versa. In Africa (and all over the world), fish species belonging to Cichlidae are often kept in aquaculture and represent a major source of food. Thus, research on the biodiversity and occurrence of monogenean species on these fish is of importance for aquaculture and conservation. The present study is a survey of the diversity of species ofCichlidogyrusin the south of the Democratic Republic of the Congo (DRC) on three cichlid species:Orthochromissp. ‘Lomami’,Serranochromiscf.macrocephalus, andTilapia sparrmaniiSmith, 1840.MethodsSpecimens ofCichlidogyruswere isolated from the gills and mounted on glass slides with Hoyer’s medium. The genital and haptoral hard parts were measured and drawn using interference contrast.ResultsIn total, six species ofCichlidogyruswere found, all new to science:C. bulbophallusn. sp. andC. pseudozambezensisn. sp. onS.cf.macrocephalus,C. flagellumn. sp. andC. lobusn. sp. onT. sparrmanii,C. ranulan. sp. onS.cf.macrocephalusandOrthochromissp. ‘Lomami’, andC. maeandern. sp. found onOrthochromissp. ‘Lomami’ andT. sparrmanii. The first four species are considered to be strict specialists,C. ranulan. sp. an intermediate generalist andC. maeandern. sp. a generalist. These parasite species show morphological similarities to species found in the Lower Guinea and Zambezi ichthyofaunal provinces, which might be explained by past river capture events between river systems of the Congo Province and both these regions.ConclusionsSerranochromiscf.macrocephalusandOrthochromissp. ‘Lomami’ can harbour respectively three and two species ofCichlidogyrus, all described in this study.Tilapia sparrmaniican harbour seven species, of which three are described in the present study. These results highlight the species diversity of this parasite genus in the Congo Basin.

Aim The formation history of Africa's current river basins remains largely unknown. In order to date changes in landscape and climate, we studied the biogeography of the African freshwater fish with the largest natural distribution. We also validated biogeographical units.Location Continental Africa.Taxon Clarias gariepinus sl.Methods We investigated mitochondrial cytb sequences of 443 individuals from 97 localities, using a haplotype network and a genetic landscape analysis. We inferred a dated phylogeny using maximum likelihood and Bayesian inference approaches and reconstructed ancestral areas with S-DEC and S-DIVA models. Microsatellite genotyping complemented the mitochondrial approach in the Congo basin, where the latter revealed complex patterns.Results Limited differentiation is found in northern and south-western Africa, and sharp genetic differentiation in the continent's east and centre. Populations with affinities to neighbouring basins occur at the edges of the Congo province. High diversity exists in the south of the Congo basin. The Zambezi province is partitioned into eastern, central and western sectors. In the east, specimens were related to those from the Congo. In the west, they were similar to Southern representatives. Phylogenetic inference placed the origin of C. gariepinus in the East Coast, with intraspecific diversification starting around the Great Lakes. These events occurred ca. 4.8-1.65 and 2.3-0.8 MYA respectively.Main conclusions Clades of C. gariepinus sl. show a clear geographical signature. The origin of C. gariepinus in the East Coast and diversification around the Great Lakes coincided with the periods of increased aridity. Low genetic differentiation in northern and southern Africa may result from connectivity during recent periods of higher rainfall. In contrast to other widespread African freshwater fish, colonization rather than extinction seemed to mediate distribution patterns. This can be explained by a high ecological tolerance. We highlight the species' suitability to study landscape and climate evolution at various scales. A.A. received a postdoctoral research fellowship from the KU Leuven and the Research Foundation - Flanders (FWO). M.V.S. and M.P.M.V. received PhD fellowships from FWO. MVS received travel grants of the FWO and the Leopold III funds for Nature Exploration and Conservation. A.C.M. received support from the Belgian Development Agency and the BTCCTB project PRODEPAAK. We sincerely thank the following colleagues for sample collection: J.-F. Agnèse, B. Benade, R. Bills, L. and G. Chapman, P. de Villiers, the late L. De Vos, J. Engelbrecht, P. Fouche, P. Galbusera, K. Goudswaard, D. Impson, R. Karssing, J. Munyandorero, A. Piers, C. Maguswi, J. Southey, the late G. Teugels, K. Van Lerberghe and the Department of Fisheries and Agriculture of Zambia. We benefited from insights from J.-F. Agnèse, T. Huyse, J. Maley, P. Skelton, J. Snoeks, K. Van Doninck and C. Sturmbauer. This study was performed on historical collections and on samples collected by researchers from certified institutes of the countries where collections were made. All material was collected prior to the implementation of the Nagoya protocol for access and benefit sharing.

In most tropical regions, the Nile tilapia (Oreochromis niloticus, Cichlidae) has been introduced for aquaculture purposes, making it one of the most widely-introduced species. Adversely, it has escaped aquaculture and became invasive in many places with detrimental effects on the local fauna. It is a fast grower and aggressive species that can hybridize with indigenous cichlids and indigenous cichlid species decline after introduction of Nile tilapia. However, little is known of the detrimental effects of co-introduction of parasites from Nile tilapia and possible parasite spillover and spillback to and from indigenous cichlids. Parasites can strongly influence the fitness and competitiveness of infected individuals and species. Therefore, it is important to monitor host switching between native and invasive fish species. The most prevalent gill parasites on Nile tilapia are Monogenea (Platyhelminthes). These are obligate parasites which have a direct lifecycle (no intermediate hosts), are species rich and generally host-specific. They mainly infect gills or skin of fish. These aspects make Monogenea ideal candidates for host switching, because they only require a single host species in the invasive area and are easily transferred. Also, because monogeneans are host-specific each host species hosts its own unique fauna of parasites, thus providing a distinguishable character between host species. The goal of this research is to trace co-introduction of Nile tilapia parasites and subsequent host switching to indigenous cichlids. To trace this, the pre-introduction (or native) parasite fauna is reconstructed by sampling hosts stored in museum collections (baseline data). Contemporary samples from the same localities are compared with the collected baseline data, which allows for a reliable tracing of host switching events. We present results from two ecoregions, Bas-Congo and Bangwuelu-Mweru, both within the Democratic Republic of the Congo. Belspo

In most tropical regions, the Nile tilapia ($Oreochromis niloticus£, Cichlidae) is introduced for aquaculture, making it one of the major species in culture worldwide. However, it has become invasive in many places with detrimental effects on the local fauna. The literature reports a decline of indigenous cichlid species after the introduction of Nile tilapia in several African regions. Here, Nile tilapia is in direct competition and can hybridize with indigenous cichlids. However, in these studies the effect of parasite co-introduction and thus of introducing additional pest species remains underexplored. Parasite co-introduction can influence the fitness and therefore the competitiveness of both invasive and native species. Also parasite spillover and spillback effects (host-switching) may occur, which can impact competition, fitness, mortality, fecundity, trophic ecology, co-evolution and biodiversity. We focus on monogenean gill parasites ($Cichlidogyrus£, $Gyrodactylus£ and $Scutogyrus£) because they are host-specific, have a high prevalence and a direct lifecycle. Furthermore, we focus predominantly on the Congo Basin because here the monogenean fauna remains largely unstudied. In addition Nile tilapia is introduced multiple times across the Congo Basin, but these introductions received little scientific attention. Studying this through regional case-studies will result in a better understanding of the potential for parasite transfer and the impact of invasive species, which will aid in conserving the native fauna. We will present a contribution to the biogeography and host range of these parasites in Haut-Katanga. In total, 13 cichlid and 19 parasite species were collected of which one cichlid and 6 parasite species are new to science and 3 need redescription. For 9 native hosts, this is the first record of their gill monogeneans. On Nile tilapia we found 5 of the 7 $Cichlidogyrus£ species known to infect this host. These 5 species also occur on the native $Oreochromis£ species in recent and historical samplings, so were already present in the basin before introduction of Nile tilapia. Furthermore, $Cichlidogyrus dossoui£ and $C. papernastrema£ were found to occur both on mouth-brooding and substrate-brooding cichlids which refutes the hypothesis of a strictly separate gill parasite fauna between mouth-brooders and substrate-brooders. BELSPO

[Figure][1] Children play on fishing boats at Lake Tanganyika, one of the East African Great Lakes threatened by oil exploitation. PHOTO: BLICKWINKEL/ALAMY STOCK PHOTO As the world's demands for hydrocarbons increase ([ 1 ][2]), remote areas previously made inaccessible by technological