Biodiversity and systematics of parasitic Crustacea infesting southern African freshwater fishes

Abstract

Crustaceans (Arthropoda: Crustacea) are regarded as the most morphologically diverse group in the phylum Arthropoda, and they have the greatest diversity of parasitic forms. Parasitic crustaceans have adapted several morphological and physiological characteristics that enable them to thrive in an array of habitats and hosts. Freshwater parasitic crustaceans are mostly found attached to the external surfaces of their host. These attachment structures are also adapted to the sites of infestation on their hosts. As a result of the pathological impacts of certain parasitic crustaceans on fish, they have been regarded as species of economic and commercial importance. Individuals from the families Argulidae, Ergasilidae, and Lernaeidae are most frequently reported throughout Africa, including both native and invasive parasite species. In southern Africa, however, these reports proved to be limited compared to other regions, therefore suggesting an underrepresentation of the actual diversity of parasitic crustaceans. In addition to scarce distribution records, only a few integrative studies from southern Africa have been carried out on some of these parasites. It was therefore hypothesised that with broader sampling across several localities and hosts in southern Africa, there will be an increased knowledge of the diversity of parasitic crustacean species present in the different river systems as well as new hosts and locality records, in addition to the possible description of new species. More so, the integration of improved morphological techniques and molecular analyses would provide novel information on the morphological characteristics of these species while adding new DNA sequences to the scanty database. In collaboration with the Aquatic Research Group of the University of the Free State, Bloemfontein, as well as several ongoing parasitology projects of the Water Research Group of the North-West University, Potchefstroom, this study aimed at linking distribution data of parasitic crustaceans with morphological and molecular data. Native and exotic fishes belonging to six families (Alestidae, Centrarchidae Cichlidae, Clariidae, Cyprinidae, and Hepsetidae) were collected from several localities in southern Africa. With an integration of morphological (light and scanning electron microscopy) and molecular (partial 18S, 28S, and COI genes) techniques, four native species (Ergasilus mirabilis Oldewage & van As, 1987; Lamproglena clariae Fryer, 1956; Lamproglena hepseti van As & van As, 2007; Lamproglena monodi Capart, 1944), three known invasive species (Argulus japonicus Thiele, 1900; Lernaea cyprinacea Linnaeus 1758; Neoergasilus japonicus (Harada, 1930)), and one new species Neoergasilus sp. nov., were described from the current study. Previous records of Ergasilus mirabilis, a widely distributed species in southern Africa, lacked genetic data. A total of 159 Clarias gariepinus (Burchell, 1822) were caught from various locations in South Africa and Zambia and adult female copepods were collected from two South African localities (Kushokwe Pan and Vaal River) and the Zambezi River in Zambia. Morphological examination confirmed the specimens as E. mirabilis with slight variability in the number of spines and setae from the original description. Molecular analyses included partial ribosomal RNA (18S and 28S) and mitochondrial DNA (COI) genes, providing genetic data to support the morphological characteristics of E. mirabilis. Additionally, new distribution records of E. mirabilis in the Phongolo Floodplain and the Vaal River are reported. The study further reported on species from the genus Lamproglena, which are gill ectoparasites found on African fish hosts in the families Cichlidae, Clariidae, and Hepsetidae. Three Lamproglena species (L. clariae, L. hepseti, and L. monodi) reported from this study are native to southern Africa. Lamproglena clariae is reported for the first time from the Phongolo Floodplain and Nyamiti Pan in South Africa, and from West Lunga in Zambezi. This study also provided genetic data using three genetic markers, which is a notable contribution to the limited molecular data available for Lamproglena species globally. Additional information on the maxillipeds, antennae, and antennules morphology of L. hepseti was also provided. New distribution records as well as the first molecular characterisation of the invasive fish lice Argulus japonicus in Sub-Saharan Africa was also provided from this study. Four fish species: Clarias gariepinus; Cyprinus carpio Linnaeus, 1758; Labeo umbratus (Smith, 1841); Labeobarbus aeneus (Burchell, 1822) were caught from seven different sites along the Orange-Vaal River System and found to be hosts for this argulid. With morphological identification and genetic analysis, parasites collected from these sites were positively identified as A. japonicus. The presence of this invasive species in the Orange-Vaal River System was confirmed and this study further adds to the available knowledge on the distribution of this species, including the addition of a possible new larval stage, and successfully links genetic data for both larval and adult stages to morphology. Lernaea cyprinacea, commonly known as an anchor worm, was also reported from this study. This copepod parasite infests various fish species worldwide and has detrimental effects on fish health. The study provided molecular characterisation of L. cyprinacea from multiple localities in South Africa. This study provided the first record of L. cyprinacea infestation in South Africa on its type host, Cyprinus carpio, Linnaeus, 1758 as well as a new host, Labeobarbus aeneus (Burchell, 1822), within the Orange-Vaal River System. Lernaea cyprinacea was additionally reported for the first time in locations within the Phongolo Floodplain and the Vaal River, and the introduction of this invasive species in the Incomati System was also noted. Lastly, the study reports on two ergasilid species from the genus Neoergasilus: N. japonicus and Neoergasilus sp. nov. Neoergasilus japonicus is an invasive ergasilid with an almost global distribution. In contrast to numerous reports from other continents, the records from southern Africa seem to be from unpublished abstracts and dissertations. This study provides the first integrative study of N. japonicus from Africa and the southern hemisphere and gives the first record of this species from the African tigerfish host, Hydrocynus vittatus Castelnau, 1861. Additionally, the novel Neoergasilus species not previously known to science is described from the sharptooth catfish, C. gariepinus. The integration of morphological identification with genetic data confirms the validity of the sequences generated and provides valuable insights into all parasite groups presented in the current study. The sequences generated for 18S, 28S, and COI are a significant contribution to future parasitic Crustacea studies in southern Africa and across other regions. This study provides an update on the distribution range of these native and invasive parasitic crustaceans in the various river systems sampled, which would serve as a base for future biodiversity and evolutionary studies. As all river systems and host species in southern Africa were not reported on, more robust sampling of other systems and from other host species is recommended for further integrative studies and evolutionary significance of these parasites.