Evaluation of the fish health assessment index in the Olifants River system, South Africa

The fish health assessment index (HAI) biomonitoring technique, developed in the USA and subsequently tested in South Africa, was re-evaluated in the Olifants River system using Clarias gariepinus, Oreochromis mossambicus and Labeobarbus marequensis during drought and flood conditions in 1994-1997 at the same sample sites in the Kruger National Park as used previously, as well as at Loskop Dam and Bronkhorstspruit Dam in the upper catchment. Parasite numbers recorded from Clarias gariepinus supported the HAI hypothesis that higher endoparasite and lower ectoparasite numbers occur at highly impacted areas. The apparent effects of pollution type on the ratio between ectoparasites and endoparasites are discussed. Environmental stressors such as flood conditions resulted in immunological responses, reflected statistically as changes in white blood cell percentage (WBC%). It is suggested that endoparasite and WBC% data provide the best overall assessment of fish condition in the Olifants River system. Modifications made to the HAI included further development of the original parasite presence/absence component into a more extensive parasite index component. The modified HAI index shows promise as a long-term biological monitoring tool in South Africa.