Application of a fish health assessment index and associated parasite index to Clarias gariepinus (Teleostei: Clariidae) in the Vaal River system, South Africa

The aim of this study was to determine if the fish health assessment index (HAI) developed in the USA and associated parasite index (PI), when applied to Clarias gariepinus at two localities in the upper and middle Vaal River system, could distinguish between localities on the grounds of water quality. Elevated HAI values, correlating with poorer chemical and physical water quality, were recorded from the Vaal River Barrage site. Parasite data were congruent with the main PI premise that prevalence and intensity of endoparasite infection would be higher at the more polluted locality, with the converse being recorded for ectoparasites. It was therefore possible to distinguish between localities with different water quality, based on parasites present on the hosts.