Persistence of microcystins and saxitoxins in tissues of wild-caught fish after an experimental depuration

Toxic cyanobacterial blooms are occurring worldwide with hepatotoxic microcystins (MCYSTs) and neurotoxic saxitoxins (STXs) frequently found together in blooms, both showing bioaccumulation in freshwater organisms. Here, we experimentally evaluated the potential depuration and concentration dynamics of MCYSTs and STXs in muscle and liver/viscera of two field exposed fish species from an anthropized reservoir in Central Mexico, Goodea atripinnis (native) and Oreochromis niloticus (the introduced Nile tilapia), during thirty-two days comprising four depuration events: 8, 16, 24 and 32 days. Despite some slight reduction in the concentrations of both cyanotoxins in the viscera of G. atripinnis at the end of the experiment, MCYSTs and STXs were still detected by the fourth depuration event in the two species in all tissues analyzed. Moreover, for O. niloticus, the concentrations of MCYSTs and STXs in liver increased by the first and fourth depuration events potentially associated with the uptake and release cycles of the toxin by hepatic cells before the complete elimination of the organism, which could be specifically tested in future studies. Our study adds evidence of a long-time persistence of cyanotoxins after an experimental depuration process, even finding an increase of MCYSTs during depuration representing a higher risk if fish are consumed, limiting the utility of this process in order to reduce the cyanotoxins exposure by humans consuming contaminated fish products. This study constitutes the first report of a long persistence of both MCYSTs and STXs simultaneously in fish tissues and our findings indicate that cyanotoxins depuration seems to be a species and tissue-dependent process.