In vitro and in vivo effects of cadmium on cholinesterases in Nile tilapia fingerlings: implications for biomonitoring aquatic pollution.

Effects of cadmium on in vitro and in vivo cholinesterase (ChE) activities of brain and muscle tissues of Oreochromis niloticus fingerlings were evaluated, considering its potential use in biomonitoring tropical water pollution. Results show that in vitro ChE activities were depressed significantly by millimolar concentration ranges of Cd(2+). The IC50 values of Cd(2+) on in vitro ChE activity in brain and muscle tissues were 1.56 and 4.31 mM, respectively. Exposure of fish to environmentally relevant concentrations of Cd(2+) (5-30 microg l(-1)) for 28 days evoked only a transient inhibition (21-34%) of in vivo ChE activities. Prior exposure and co-exposure of fish to 15 microg l(-1) of Cd(2+) enhanced the extent of inhibition of ChE levels induced by the organophosphorous insecticide chlorpyrifos. As high concentrations of cadmium have the potential to depress ChE activities, monitoring of metal levels in water bodies with suspected high levels of metal inputs is necessary to accurately interpret the fish ChE inhibition data in relation to insecticide contaminations.