Abstract
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.
Highlights
In recent years there has been an increasing awareness that parasitism should be investigated in view of undesirable environmental conditions such as organic and inorganic pollution arising from anthropogenic activities (Marcogliese 2005)
The return water dam had the highest concentrations of nutrients amongst all sites and were consistently above the levels set by the South African target water quality range (TWQR) (Table 1)
The Flag Boshielo Dam was positively associated with dissolved oxygen (DO) content and iron level but negatively associated with arsenic level (Figure 1)
Summary
In recent years there has been an increasing awareness that parasitism should be investigated in view of undesirable environmental conditions such as organic and inorganic pollution arising from anthropogenic activities (Marcogliese 2005). Environmental conditions are important for a host’s survival and well-being (Sures 2008). For heteroxenous (indirect life cycle) metazoan parasites, environmental conditions must be favourable for all host levels (i.e. intermediate and final hosts) and for free-living stages of the parasites (Dzikowski, Paperna & Diamant 2003). Monoxenous (direct life cycle) metazoans, which are normally ectoparasites, are in constant contact with water, suggesting that poor water quality may adversely affect their diversity to a greater extent (Avenant-Oldewage 2001; Pietrock & Marcogliese 2003). Populations of both heteroxenous and monoxenous parasites are expected to be affected by changing environmental conditions
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