A comparative assessment of the health status of feral populations of Clarias gariepinus from three dams in the Limpopo and Olifants river systems, Limpopo province, South Africa, using the fish health assessment index protocol

Abstract

An evaluation of the health status of feral populations of the freshwater catfishClarias 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.

Keywords: biomonitoring, Flag Boshielo Dam, inverted parasite index, Luphephe–Nwanedi Dams

African Journal of Aquatic Science 2012, 37(1): 27–37