The assessment of metazoan parasite diversity of native and extralimital Clarias gariepinus (Burchell, 1822) populations : a holistic approach

PhD (Science with environmental Sciences), North-West University, Potchefstroom Campus

Parasites contribute substantially to global biodiversity. Similarly, parasites of aquatic species have a vast unexplored diversity, and in recent years received increasing attention, contributing to the global aim of scientists to catalogue the entirety of the world’s biodiversity. Simultaneously, it became apparent that the diversity of parasites, as well as their assemblages within ecosystems, represent a complex interconnectivity of various components of an ecosystem and is not solely a reflection of the diversity or presence and absence of species. These macro- and microscopic organisms contribute to the dynamics of interactions between humans, the environment, and the hosts within said environments. Thus, leading to the present study that investigated diversity of the pan-African distributed sharptooth catfish, Clarias gariepinus (Burchell) in several geographic regions within southern Africa that is greatly underrepresented in parasitological data. This study provides an overview on the validity and biogeography of the more than 107 metazoan parasite species currently known from C. gariepinus, and the number of listed digenean species known from this host is amended from 34 to 36. Furthermore, 44 parasitic species across the major taxonomic groups (Monogenea, Digenea, Cestoda, Nematoda and Crustacea) representing 12 orders and 19 families were recorded from various localities in southern Africa during this study. Of these, eight species are novel to the parasite fauna of C. gariepinus, 33 taxa are already known, and three species utilised the sharptooth catfish as paratenic host. Community assemblages were distinct across all sampled populations, and diversity and abundance [species richness (S)] varied greatly, with highest diversity recorded in the Upper Zambezi River system: Barotse floodplain (S = 31) and Kabompo River (S = 15) in Zambia, while catfish from the Lower Phongolo River and floodplain (S = 17) harboured the most diverse parasitic community in South Africa compared to the lower diversity found from populations in the Boskop Dam (BS) (S = 14), Vaal River (VR) (S = 13), Sand River (SR) (S = 10), Riet River (RR) (S = 9) and Gariep Dam (GD) (S = 8) on the Orange-Vaal River system. The parasite diversity and abundances from two translocated populations, one in the Great Fish River (GFR) (S = 9) and Riviersonderend River (RSE) (S = 7) were similar, however community assemblages were distinct. The GFR populations shared a similar community assemblage compared to its source population from GD, while RSE had a distinct community assemblage. The resilience of 12 parasitic species is confirmed, in their persistence upon co-introduction into novel environments, and provided support for the enemy release hypothesis on loss of native parasites upon entering a new environment. Two alien invasive species, Argulus japonicus Thiele, 1900 and Schyzocotyle acheilognathi (Yamaguti, 1934) were also found to parasitise C. gariepinus. The former in GD, while S. acheilognathi most probably spilled back to the translocated C. gariepinus in RSE from another alien invasive, Cyprinus carpio, already present in the system. Furthermore, a novel parasitic copepod species, Ergasilus sp. A was found on the gills of both translocated populations and suggests a spillback event from an unknown native host to the introduced C. gariepinus in GFR and RSE. The complexity and tolerance of parasitic taxa were illustrated in the absence of complex life cycle species from some native distribution populations, but presence in translocated populations, indicating that the ecosystems where they occur support similar host (intermediate or definitive) assemblages or that the parasites can adapt to a new host-parasite system in a novel environment. Finally, the responses of parasitic taxa to functional host traits and their environment (unimpacted or impacted), as well as inverse responses to increased elements, or in the case of positive responses to Au, Fe, Co, Hg, Sn and Se by respective taxa, indicate that the effect of pollutants on different organisms in aquatic environments is more complex than linking a generalised concept of pollution to species (intermediate and definitive hosts) absence or presence, or increased morbidity.

Doctoral