Microcystins distribution, bioaccumulation, and Microcystis genotype succession in a fish culture pond

In freshwater aquaculture ponds, cyanobacterial blooms and microcystins (MCs) pollution have attracted considerable attention due to their toxic effects. To provide an insight into cyanobacterial problems in aquaculture ponds, MCs distribution, bioaccumulation, and Microcystis genotype succession in a fishpond were investigated from May 2017 to November 2017. The distribution of MCs in filtered water, seston, and sediment varied considerably among months. MCs concentrations in filtered water, seston, and sediment ranged from 1.16 to 3.66 μg/L, 0.64 to 13.98 μg/g DW, and 1.34 to 5.90 μg/g DW, respectively. In addition, chemical oxygen demand was positively correlated with sestonic MCs concentrations. MCs concentrations accumulated in different tissues of market-size fish were in the order of liver > kidney > intestine > muscle. MCs content in muscle was 4.3 times higher than the WHO recommended tolerable daily intake level. Twenty-four ITS genotypes of Microcystis were identified from a total of 653 sequences. During the survey period, considerable genotype variation and rapid genotype succession were observed and dominant genotype was absent. A redundancy analysis revealed that Microcystis genotypes could significantly influence the variations in the proportions of the potentially toxic Microcystis, which could in turn influence the MCs concentrations in seston.