Diversity of metazoan parasites of the Mozambique tilapia, Oreochromis mossambicus (Peters, 1852), as indicators of pollution in the Limpopo and Olifants River systems

Aquatic systems are affected by a variety of anthropogenic activities that decrease water quality through the introduction of organic and inorganic pollutants. To investigate the relationship between fish parasite communities and water quality, metazoan parasites were examined in 140 specimens of the Mozambique tilapia (Oreochromis mossambicus) sampled in three lakes in the Limpopo Province, namely the Luphephe-Nwanedi Dams (regarded as unpolluted), the Flag Boshielo Dam (regarded as moderately polluted) and a return water dam on a mine site (regarded as polluted). The monogenean parasites Cichlidogyrus halli, digenean larval stages of Clinostomum and Diplostomum spp. and a gryporynchid cestode were found in or on O. mossambicus in all the sampled sites. The distribution of monogeneans (Cichlidogyrus sclerosus, Cichlidogyrus dossoui, Cichlidogyrus tilapiae, Scutogyrus longicornis and three Enterogyrus spp.), metacercarial stages of two digeneans (Neascus and Acanthostomum spp.) and nematodes (an unidentified nematode, Contracaecum sp., Paracamallanus cyathopharynx and Procamallanus laevionchus) was limited to the unpolluted and moderately polluted lakes. Larval stages of Diplostomum sp. were present in O. mossambicus collected from the unpolluted and polluted sites. The variability of the calculated infection indices (prevalence, mean abundance and mean intensity) and the parameters of species richness and diversity suggest that the structure of parasite communities are affected by the pollution levels of the water. The unpolluted reference site had the highest species richness and the highest overall parasite abundance values.