The use of different enzymes in feral freshwater fish as a tool for the assessment of water pollution in South Africa.

Selected enzymes in the organs/tissues of two fish species (Oreochromis mossambicus and Labeo umbratus) were evaluated as biomarkers of water pollution in warm- and cold-water systems. The fish were caught using standard techniques during two high-flow and two low-flow surveys. The results indicated that the fluctuating enzyme activities measured were not a result of pollution but could be initiated as a result of (1) no or too little pollution, (2) handling of the fish, and (3) struggling in the nets. Furthermore, most of the enzymes are nonspecific for the specific pollutants present. It is concluded that the selected enzymes could not be successfully employed as biomarkers of water pollution when the organisms are sampled from a polluted water source.