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.

The relationship between parasite species diversity and organic pollution in the upper Manyame catchment, Zimbabwe, was investigated between October 2006 and January 2007. The parasite assemblage comprised 13 species in total. Species richness in the unpolluted sites was high; in the moderately polluted sites, it was low, while in the polluted sites, only one parasite species was encountered. Component community diversity, as measured by the Shannon index (H 0 ), decreased with increase in organic pollution. The distribution and occurrence of ectoparasites (Dolops ranarum, Lamproglena clariae, Chonopeltis sp. and Macrogyrodactylus sp.) and one endoparasite (Lytocestus sp.) were limited to the unpolluted sites, demonstrating their sensitivity to organic pollution. The prevalence of the nematodes Paracamallanus cyathopharynx, Procamallanus laevionchus and Contracaecum spp. larvae decreased along the pollution gradient, showing their high sensitivity to organic pollution. The platyhelminths Diplostomum sp. and Polyonchobothrium clarias were the most tolerant and occurred at both polluted and unpolluted sites. Proteocephalus sp. and Caryophyllaeus sp. were limited to the polluted sites, probably as a result of high abundance of oligochaetes and copepods, their intermediate hosts that thrive in sewage-enriched sediments, at the downstream sites. The observed results assume that the decrease in parasite diversity can be related to increased organic pollution. Some parasites requiring complex life histories were absent along with pollution-related disappearance of their vector hosts. Further studies should address the identification of parasite life stages that are more sensitive to pollutants.

An investigation was conducted into the parasitic infection of an indigenous cichlid, Oreochromis mossambicus, collected seasonally from the Nwanedi-Luphephe dams of the Limpopo River System from July 2007 to April 2009. Of 157 host specimens examined, 115 (73.25%) were infected by at least one gill parasite. In all, 1565 monogenean specimens were collected, belonging to five different species and two genera: Cichlidogyrus (C. halli, C. sclerosus, C. tilapiae and C. dossoui) and Scutogyrus (S. longicornis). Infracommunities were poor, with only 27 (17.20%) hosts harbouring four of the five species observed. Cichlidogyrus halli was the dominant species, with a prevalence of 73.25%. Prevalence values for each of the other four species were less than 50%. The mean intensities for each of the five species were low ( < 8 parasites/host). The parasite abundance and intensity levels were not influenced by either the sex or the size of the host. The abundance of all parasite species except for S. longicornis exhibited seasonal fluctuations, reaching peaks in winter and summer. The spatial distribution of each parasite was studied on different regions of the gill, and positive associations among some species were revealed.

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An evaluation of the health status of feral populations of the freshwater catfish Clarias gariepinus was carried out between 2009 and 2010 at three dams in the Limpopo and Olifants river systems with varying levels of human impact. Fish health was assessed using a modified health assessment index (HAI) protocol, with the inclusion of the inverted parasite index (IPI) and condition factor (K). These biomonitoring tools provide relatively simple and rapid indications of how well fish are coping in their environment. To verify the biomonitoring results, water quality analyses were included in the study. The nutrients and mining-related pollutants in the three dams differed to a great extent and showed an increasing trend in the order: Luphephe-Nwanedi Dams < Flag Boshielo Dam < Return Water Dam. The HAI score varied across the three sampling sites, with individual mean values of 93.3, 84 and 42.7 at the Return Water Dam, Flag Boshielo Dam and Luphephe-Nwanedi Dams, respectively. The top six metrics that correlated best with fish health scores were the levels of ectoparasites, haematocrit values and the condition of the gills, liver, skin and fins. Although the HAI successfully differentiated among the three localities, which differed in water quality, it was non-specific in response to contaminants. Notably, the premise set forth by the IPI that endoparasites increase with a decrease in water quality was not supported.

Examination of 40 specimens of Pseudocrenilabrus philander philander (Weber, 1897) collected from Padda Dam (26°10′S; 17°59′E), South Africa revealed the presence of a stomach monogenean of the genus Enterogyrus (Paperna, 1963). The monogenean presented a prevalence of 52.5 % and mean intensity of 4.2. The body, surrounded by a thick cuticle which is striated transversally, is dorso-ventrally flattened. The haptor has two pairs of gripi, a lightly sclerotised ventral transverse bar and marginal uncinuli. The dorsal gripus has a bifurcate root and a curved blade which is shorter than the shaft and is larger than that of the ventral gripus. The genetic distance between E. coronatus and the present Enterogyrus species (0.24 %) confirms the morphological similarities. This study presents a new locality and host record of the genus Enterogyrus from South Africa and a review of the morphology and distribution of Enterogyrus species is also given.