Abstract
Background Monogenean 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).
Methods Oreochromis 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.
Results A 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).
Conclusions This 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.
Background
Across the African continent, the Congo basin harbours the greatest species richness of fish [1-2]. The Congo basin covers 3,747 320 km2, and drains most of the Democratic Republic of Congo and parts of some of its bordering countries (Angola, Zambia, Tanzania, Burundi, Rwanda, Central African Republic and Republic of Congo) and a small part of Cameroon [3]. The Congo basin includes different types of habitats and is subdivided into sections: Upper Congo (called Lualaba), Middle Congo, and Lower Congo [2,4-5]. One of the major tributaries in the Upper Congo drainage is the Lufira River [6]. The Lufira River is subdivided into three sections: the Upper Lufira (from the source of the river to Lake Koni), the Middle Lufira (from downstream Lake Koni to the Kyubo Falls), and the Lower Lufira (from downstream the Kyubo Falls to the Kamalondo Depression, at the junction with the Lualaba River) [5,7]. In order to provide hydroelectric power, two successive dams were built in the Upper Lufira River; this created two artificial Lakes, Tshangalele (1930) and Koni (1949) [8-10]. Lake Tshangalele, located about 35 km east of the town of Likasi, holds a variety of fish, and it is also an UNESCO Man and the Biosphere Reserve, rich in birdlife [11-12]. In the Lufira River, most studies undertaken on biodiversity focused on vertebrates such as fish and birds [13-16]. Vast and speciose communities, which are often dominated by less sizeable animals such as flatworms or various parasite taxa, remain understudied, as is the case all over the world [17-18]. In view of the high biodiversity of potential host species in the tropics, it can be expected that parasitological surveys there would lead to the recording of many parasite species, including species new to science [19-20]. This study focuses on monogenean fish parasites due to their diversity, wide distribution, high host-specificity and single-host lifecycle, rendering them interesting models for studying the extent of parasite biodiversity and the underlying diversification mechanisms [21]. Monogeneans are common parasitic flatworms (Platyhelminthes) mostly infecting fish, and sporadically aquatic invertebrates, amphibians, reptiles and a single species of mammal (the hippopotamus) [22-27]. Infection sites of monogeneans on fish are typically gills, fins and/or skin [28], however they are also found rarely in the stomach, urinary bladder, intestine, oral or nasal cavity, eyes and heart [29-30]. Because of their one-host lifecycle and their close relationship with their host species, many monogeneans are specialists, infesting only a single host species (oioxenous specificity), though others are generalists, infesting two or more host species (stenoxenous specificity) [31-33]. Mendlová and Šimková [34] used a more extensive number of categories of host specificity on the basis of the phylogenetic relationships among (cichlid) host species. Parasites can be: (1) strict specialists when infecting only one host species; (2) intermediate specialists when infecting two or more congeneric host species; (3) intermediate generalists when infecting noncongeneric cichlid species belonging to the same tribe; and finally (4) generalists, when infecting noncongeneric cichlid species of at least two different tribes. African cichlids (taking also into account the Levant) are known to harbour monogenean parasites belonging to six genera: Enterogyrus Paperna, 1963; Urogyrus Bilong Bilong, Birgi & Euzet, 1994; Onchobdella Paperna, 1968; Scutogyrus Pariselle & Euzet, 1995; Cichlidogyrus Paperna, 1960 (Dactylogyridea) and Gyrodactylus von Nordmann, 1832 (Gyrodactylidea). The latter four are ectoparasitic genera, and among them, Cichlidogyrus is the most species-rich group with more than 138 nominal species described to date [35-37]. This study aims to record the monogenean parasite fauna of three cichlid fishes in the Upper Lufira basin; these parasites were never formally reported from this region. Objectives include: (i) inventorying the diversity of gill monogenean communities, and (ii) analyzing infection parameters of these monogenean parasites.
Methods
Study area
This study was conducted in the Upper Lufira basin (Figure 1), which is localized across the mining hinterland area in the west of the Haut-Katanga province (in the south of the former Katanga province). The climate is of type AW6 following the classification of Köppen [38], a rainy tropical climate with a rainy season extending from November to April [39]. Most precipitation falls from December to March [40]. Fishing is done essentially for Coptodon rendalli (Boulenger, 1896), Oreochromis mweruensis Trewavas, 1983, Serranochromis macrocephalus Boulenger, 1899, Clarias gariepinus (Burchell, 1822) and Clarias ngamensis (Castelnau, 1861) [12, 41]. Captured fish are intended for human consumption, for a small part by the local population around the Upper Lufira basin, and for most part in bigger towns such as Likasi and Lubumbashi.
Fish sampling
Three fish species, Oreochromis mweruensis, Coptodon rendalli and Serranochromis macrocephalus were selected for the study, given their economic value and their abundance in the Upper Lufira basin [12, 41]. Fish were collected using nets or were bought from fishermen along the shores of the Lufira River, Lake Tshangalele and Lake Koni (Figure 1) between September 2015 and August 2018. Fish were kept alive in an aerated tank, and transported to a field laboratory. Fish were identified up to the species level following the keys by Skelton [42] and Lamboj [43]. Fish were killed by severing the spinal cord just posterior to the cranium, immediately prior to examination, following Olivier et al. [44]. Fish were processed as the total length (TL) and the standard length (SL) were measured to the nearest centimetre, and the weight was taken in gram for each fish.
Parasite sampling
To collect monogenean parasites, fish were dissected and the right gill arches removed by dorsoventral section. One fish amongst all the fishes sampled was randomly dissected and inspected for monogenean parasites in its stomach. Gill arches and the stomach were placed in a Petri-dish containing water for examination using a stereomicroscope Optica 4.0.0. Parasites were dislodged from the gill filaments using entomological needles and fixed between a slide and cover slip into a drop of either Hoyer’s medium or ammonium picrate-glycerin (a preparation described by Malmberg, 1957) according to Nack et al. [45]. Twenty-four hours later, coverslips were sealed using nail varnish. Parasites were deposited in the invertebrate collection of the Royal Museum of Central Africa (RMCA) under accession numbers XXX.
Monogenean community composition, indices of diversity and infection parameters
Morphological identifications of the retrieved parasite specimens were conducted based on the sclerotized parts of the haptor, the male copulatory organ (MCO) and the vagina, using an Optica BA310 and a phase-contrast Olympus BX50 microscope. Parasite identification up to species level, and comparison with known congeners was based on García-Vásquez et al. [46-47], Přikrylová et al. [48-49], Gillardin et al. [50], Muterezi et al. [51], Pariselle and Euzet [35,52], and Fannes et al. [53]. Parasite diversity was summarized by the species richness index (S), indices of Shannon (H) and Equitability of Pielou (J). Infection parameters: prevalence (P), mean intensity (MI) and mean abundance (MA) were provided following definitions given by Margolis et al. [54] and Bush et al. [55]. Statistical analysis was performed using Past 3.1 software.
Results
Fish processed for the study had different size and weight range. For Oreochromis mweruensis (n=47) the mean TL was 18.2 ± 4.1 cm and 14.6 ± 3.2 cm for the mean SL, and the mean weight was 72.7 ± 38.8 g. For Coptodon rendalli (n = 28) the mean TL was 15.1 ± 2.8 cm and 12.0 ± 2.4 cm for the mean SL, and the mean weight = 72.7 ± 38.8 g. For Serranochromis macrocephalus (n = 11) the mean TL was 16.9 ± 3.4 cm and 14.0 ± 2.8 cm for the mean SL, and the mean weight was 81.9 ± 51.5 g.
Monogenean community composition and indices of diversity in the Upper Lufira basin
Representatives of four genera of monogeneans, Cichlidogyrus, Gyrodactylus and Scutogyrus (on the gills) and Enterogyrus (in the stomach), were collected (Table 1). Among them were ten known species of Cichlidogyrus, one species of Gyrodactylus, two species of Scutogyrus and one species of Enterogyrus. Parasite diversity indices were reported to be 10, 6 and 2 for S; 1.5, 1.2 and 0.6 for H; and 0.6, 0.8 and 0.8 for J respectively for O. mweruensis, C. rendalli and S. macrocephalus. The distribution of monogeneans per sampling period or per season is shown in Table 2.
Infection parameters of monogenean parasites in the Upper Lufira basin
Prevalence, mean intensity and mean abundance presented in this section take into account hosts grouped without seasonal subdivision.
The highest prevalences recorded was 80.9% for C. halli on O. mweruensis, 92.3% for C. dossoui on C. rendalli, and 9.1% for both C. zambezensis and C. karibae on S. macrocephalus. A low prevalence of 2.1% was recorded for C. tiberianus, S. cf. bailloni for O. mweruensis, and 3.8% for G. nyanzae from C. rendalli (Figure 2).
For G. nyanzae the highest MI = 8.7± 9.9 was recorded from O. mweruensis and a low of MI= 1 ± 0 from C. rendalli. Conversely C. papernastrema obtained a MI of 17.1 ± 24 when examining the latter fish host. For S. macrocephalus, C. karibae was the parasite with the highest mean intensity (MI= 15) and C. zambezensis the lowest (MI= 5) (Figure 3).
The results regarding the mean abundance reveal that on O. mweruensis, C. halli (MA= 6.4 ± 7.7) is the most abundant species; on the gills of C. rendalli, C. dossoui (9.7 ± 15.6) is the most abundant species; and the highest abundance of monogeneans on S. macrocephalus is 1.4 ± 4.5 per examined fish for C. karibae (Figure 4).
Discussion
This research was conducted to explore the monogenean parasite fauna of three economically important and abundant cichlid species in the Upper Lufira basin, a part of the Upper Congo basin. In this study thirteen gill and one stomach monogenean species were recorded. Parasite species were already reported from fish belonging to the genera Oreochromis, Coptodon and Serranochromis [35,51, 56]. Although few studies on monogenean parasites from the Congo basin have been conducted in the Lake Tanganyika, Bangweulu-Mweru, Upper Lualaba, Kasai, Lower Congo and Pool Malebo Ecoregions (sensu Thieme et al. [57]) (e.g. Vanhove et al. [58]; Gillardin et al., [50]; Muterezi et al. [51]; Jorissen et al. [56, 59-60]; Geraerts et al. [61]), this study is the first to record monogenean parasites in the Lufira basin.
The known host range of five parasite species is extended in this study. Cichlidogyrus quaestio, S. cf. bailloni and E. malmbergi were recorded for the first time from O. mweruensis; C. halli from C. rendalli; and C. karibae from S. macrocephalus. Cichlidogyrus karibae was described by Douëllou [62] on Sargochromis codringtonii (Boulenger, 1908) in Lake Kariba (Zambezi basin, Zimbabwe). Enterogyrus malmbergi was described by Bilong Bilong [63] from the stomach of Oreochromis niloticus (Linnaeus, 1758) in the Sanaga River (Cameroon). Scutogyrus bailloni was formally described by Pariselle and Euzet [52] on Sarotherodon galilaeus (L, 1758) in the Mékrou River (Niger basin, Niger, West Africa). Since only a single similar parasite specimen was retrieved in this study on the gills of O. mweruensis, it cannot be assigned to S. bailloni with certainty. Nevertheless these (putative in case of S. bailloni) records substantially expand the known geographical distribution of these three monogenean species. Considering species richness, our results are similar to previous reports of monogenean gill parasites for these fishes in the Congo basin. In this study, ten monogenean species were found on O. mweruensis, while Jorissen et al. [56, 59] collected nine parasite species in the Bangweulu-Mweru ecoregion on O. mweruensis (of which seven are shared, except for Cichlidogyrus mbirizei, C. quaestio and S. cf. bailloni on O. mweruensis from the Lufira river system, and C. cirratus and C. papernastrema on O. mweruensis from the Bangweulu-Mweru ecoregion). Six monogenean species were found on C. rendalli in this study, while Jorissen et al. [59] collected five parasite species (all but C. halli corresponding to those found in this study) in the Bangweulu-Mweru ecoregion. On S. macrocephalus, two monogenean species (C. karibae and C. zambezensis) were found in this study while Jorissen et al. [59] reported only the last species, on fewer host fish.
In terms of infection parameters, on O. mweruensis, one parasite species had a prevalence higher than 50% in the Upper Lufira basin (C. halli, P= 80.9%) against two monogenean species in the Bangweulu-Mweru reported by Jorissen et al. [59] (P= 57.1% for C. dossoui and S. gravivaginus). On C. rendalli, C. dossoui (P= 92.3%) in the Upper Lufira basin, and C. dossoui, C. quaestio and C. tiberianus in the Bangweulu-Mweru, have P>50% following comparison with Jorissen et al. [59]. On S. macrocephalus, no parasite species had a prevalence higher than 50% in the Upper Lufira basin, while C. zambezensis reaches a prevalence of 100% in the Bangweulu-Mweru. Regarding the infection intensity (Table 1), on O. mweruensis, in the Upper Lufira basin, the most infected fish harbour up to 30 specimens of C. halli, followed by 25 specimens of G. nyanzae, against 37 parasite specimens of G. nyanzae and 21 parasite specimens of C. cirratus in Bangweulu-Mweru (reported by Jorissen et al. [59]). On C. rendalli in the Upper Lufira basin, the most infected fish harboured up to 84 specimens of C. papernastrema, followed by C. dossoui with 68 monogenean specimens against respectively 29 and 20 specimens of C. dossoui and C. quaestio in the Bangweulu-Mweru Ecoregion. Finally, on S. macrocephalus in the Upper Lufira, the most infected fish contain up to 15 and 5 parasite specimens of C. karibae and C. zambezensis respectively while Jorissen et al. [59] reported 21 parasite specimens of C. zambezensis in the Bangweulu Mweru. These differences in infection parameters may be due to sample size, season, biogeographical distribution or other environmental parameters, as communities of cichlid-infecting monogeneans have been observed to fluctuate e.g. seasonally and between habitat types, and parasite species composition may change between areas and basins [64-66].
Conclusion
We reported stomach and gill monogenean species richness and infection parameters from three cichlid species in the Upper Lufira basin. A total of 13 monogenean species were recovered from O. macrochir, C. rendalli and S. macrocephalus. These findings are the first record of monogeneans in the Upper Lufira basin. For future sampling, it will also be interesting to study other groups of fish parasites other than monogenean parasites, as well as other fish species or families, to record the diversity of parasites [56, 59]. In addition, parasites can also be used as bioindicators of water quality [67-69] in this ecosystem where there is a substantial anthropogenic threat, especially from mine pollution [70-71]. The use of parasites as bioindicators of environmental conditions has been applied previously on African cichlids [72]. This study can serve as a baseline whereby future studies conducted on fish from the Upper Lufira basin can be compared to this study so as to establish if there has been a change in parasite composition and parasite load over time.
Funding
This research was carried out with the funding support of a VLIR-UOS South Initiative (ZRDC2014MP084); at the time of conducting this investigation, M.P.M Vanhove was supported by the Belgian Directorate-General for Development Cooperation and Humanitarian Aid [CEBioS program: Capacities for Biodiversity and Sustainable Development], and currently by the Special Research Fund of Hasselt University (BOF20TT06). The South African team was supported by the South African Research Chairs Initiative of the Department of Science and Innovation and National Research Foundation of South Africa (Grant No 101054).
Availability of data and materials
Slides of monogenean parasites are available in the invertebrate collection of the Royal Museum of Central Africa, Tervuren, Belgium.
Authors’ contributions
ACM, JS and MPMV designed and supervised this study. ACM, EA, EJV contributed to sampling, the collection and identification of fish. FMB, WJLP, WS, JRS and MPMV helped with the collection and preparation of the gill parasites. AP, MWPJ, MPMV helped with the morphological identification of parasites species. MPMV helped with the writing of the paper, analysis of the data, interpretation and discussion of results and provided scientific background in the field of monogenean research. All the authors critically read and edited the manuscript, and approved the final manuscript.
Ethics approval and consent to participate
Fish were collected using nets or were bought from fishermen. In the absence of relevant animal welfare regulations in the DRC, we had used the guidelines and authorization in accordance with the Unité de Recherche en Biodiversité et Exploitation durable des Zones Humides (BEZHU) of the Université de Lubumbashi
Consent for publication
Not applicable
Competing interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
VLIR-UOS is thanked for supporting this study through the South Initiative « Renforcement des capacités locales pour une meilleure évaluation biologique des impacts miniers au Katanga (RD Congo) sur les poissons et leurs milieux aquatiques », the local team of the University of Lubumbashi (BEZHU) namely C. Kalombo Kabalika, P. Kiwele Mutambala, B. Katemo Manda, M. Kasongo Ilunga Kayaba and C. Mukweze Mulelenu for their help in fish sampling, the international team, I. Přikrylová, for her contribution in confirmation of parasite identification, and F.A.M. Volckaert (KU Leuven) and L. Janssens de Bisthoven (Royal Belgian Institute of Natural Sciences) for hosting G.K. Kasembele in their teams during his respective research visits to Belgium. Finally, we thank the Institut Congolais pour la Conservation de la Nature (ICCN) for facilitating and authorising sampling.
Footnotes
GKK: jrskasembele{at}gmail.com
ACM: augustechocha{at}gmail.com
EA: emmanuelabwe{at}gmail.com
AP: antoine.pariselle{at}ird.fr
FMB: fidel.muterezi{at}gmail.com
TH: Tine.Huyse{at}africamuseum.be
MWPJ: michiel.jorissen{at}uhasselt.be
EJV: emmanuel.vreven{at}kuleuven.be
WJLP: wilmien.powell{at}ul.ac.za
WS: willem.smit{at}ul.ac.za
JRS : joseph.sara{at}ul.ac.za
JS : jos.snoeks{at}kuleuven.be
MPMV : maarten.vanhove{at}uhasselt.be