Cyanobacterial abundance and microcystins in water, seston and fish tissues in Lake Hora-Arsedi (Ethiopia)

Abstract

The phytoplanktonic composition with a focus on cyanobacteria, intra- and extracellular microcystins (MCs) concentrations and MCs concentrations in fish tissues were investigated in Lake Hora-Arsedi (Ethiopia). The phytoplankton community comprised of 40 species in the first phase of the study and was dominated by cyanobacteria and dinoflagellates. Considerable concentrations of both intra- and extracellular MCs were detected. Total extracellular MCs concentrations in water of up to 2.99 µg l⁻¹ were detected, with the highest level almost three times the WHO tolerable daily intake (TDI) limit for MC-LR in drinking water. The MCs concentration in algal seston measured in April 2015, 1.138 µg g⁻¹ dry weight (DW), was higher than that recorded in March 2015 (0.825 µg g⁻¹ DW). Among the three MCs congeners for which we had standards, MC-LR and MC-YR accounted for 71.5 and 28.5%, respectively, of the total MCs measured in the water samples, whereas MC-RR was below the detection limit of the method of analysis used. The total MC concentration in the liver of Oreochromis niloticus was 14.42 µg g⁻¹ DW in March although the MC concentration in April was not measurable in the liver sample of the same species, O. niloticus. Conversely, the total MC concentrations in the liver samples of Tilapia zillii collected in March and April were 15.21 and 17.8 µg g⁻¹ DW, respectively. The results suggest that there is considerable potential for knock-on effects of toxic algae blooms on humans through consuming water and fish from Lake Hora-Arsedi.

Keywords: algae, composition, Oreochromis niloticus, physico-chemical properties, phytoplankton, water quality