Concentrations of microcystins in the muscle and liver tissues of fish species from Koka reservoir, Ethiopia: A potential threat to public health

Herein, we report the presence and concentrations of three most common variants of microcystin (MC-LR, -RR and -YR) in the liver and muscle tissues of wild Nile Tilapia (Oreochromis niloticus), Common Carp (Cyprinus carpio) and African Sharp Tooth Catfish (Clarias gariepinus), which were collected from two study sites of the present study on Koka reservoir, Ethiopia. A total of 36 fish liver and 36 fish muscle samples were collected for six months. Microcystins (MCs) were quantified using LC-ESI-HRMS. The results show that MCs were found in most of the fish liver samples, while they were below the detection limit of the method of analysis used in the muscle samples. In addition to the three most common congeners of MCs, eight other microcystin variants and cylindrospermopsin were detected in the fish liver samples although further detailed study is needed. Among the three most common MC congeners, MC-LR was more prevalent than MC-RR and MC-YR in the liver samples of the three fish species. The highest MC concentration was found in Nile Tilapia collected in April (591.60 μg/g DW of MC-LR), whereas the lowest detected concentration was in Catfish collected in March (2.23 μg/g DW of MC-RR). The results of this study suggest that further intensive assessment and monitoring of the reservoir from different perspectives should be conducted in order to reduce the concentrations of the MCs and seek solutions to the potential public health risk. Moreover, this is the first study ever to report detailed quantification of MCs in fish liver and muscle samples collected from Ethiopia.