Microcystin-LR equivalent concentrations in fish tissue during a postbloom Microcystis exposure in Loskop Dam, South Africa

摘要

The effects of a decomposing cyanobacteria bloom on water quality and the accumulation of microcystin-LRequivalent toxin in fish at Loskop Dam were studied in May 2012. Enzyme-linked immunosorbent assay [ELISA]was used to confirm the presence of microcystin-LR equivalent in the water and to determine the microcystin(MCYST) concentration in the liver and muscle of fish. The lowest concentration of extracellular MCYST-LRequivalent was recorded in the lacustrine zone, where no cyanobacterial cells were observed, while the highestconcentration (3.25 μg l−1), 3.25 higher than World Health Organization standard, was observed in the riverinezone. Extremely high MCYST-LR equivalent concentrations of 1.72 μg MCYST-LReq kg−1 in the liver and 0.19 μg kg−1in muscles of Labeo rosae, and 2.14 μg MCYST-LReq kg−1 in the liver and 0.17 μg kg−1 in muscles of Oreochromismossambicus, indicate that the consumption of sufficient fish biomass might cause severe adverse effects inhumans. Microscopic analyses of the stomach content of both fish species revealed low numbers of cyanobacterialMicrocystis aeruginosa cells in comparison to other phytoplankton. The extracellular MCYST-LR equivalent of thedecomposing bloom may have played a major role in the high levels observed in the livers of the two fish species.These findings are important for all downstream water users.