Sublethal Toxicity of Microcystis and Microcystin-LR in Fish

The occurrence of blooms of toxic cyanobacteria in freshwater environments is a global ecological and public health concern. Species of Microcystis are of particular importance because blooms occur in many freshwater environments throughout the world and microcystin toxin concentrations can exceed World Health Organization advisory levels. While microcystin has been associated with fish kills, sublethal effects of chronic exposure at environmentally relevant concentrations are relatively unknown. The objective of this research was to evaluate toxicity of microcystin and Microcystis in fish during all life history stages. We evaluated global gene expression response in larval zebrafish (Danio rerio), and a sub-set of biomarker genes indicative of microcystin exposure were identified. In addition, vitellogenin genes were highly up-regulated in zebrafish exposed to Microcystis but not the microcystin toxin, indicating potential endocrine disrupting effects of Microcystis blooms. Effects on reproduction were evaluated in adult zebrafish exposed to Microcystis. There was a significant decrease in the percentage of adults that spawned, however fecundity and larval survival were not affected. Laboratory mesocosm experiments with channel catfish (Ictalurus punctatus) were also conducted to determine the importance of dietary and aqueous exposure in microcystin bioaccumulation and assess histopathological lesions. Tissue toxin concentrations and histopathological lesions were also evaluated in channel catfish collected from Lake Erie and Waterville Reservoir, North Carolina to monitor fish living in environments affected by Microcystis blooms and relate responses to those observed in laboratory exposures.