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

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