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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

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.

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.

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.

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.