The presence of microcystins in fish Cyprinus carpio tissues: a histopathological study

The occurrence of heavy cyanobacterial blooms has become a worldwide problem, as a consequence of eutrophication of the aquatic ecosystems; furthermore, 60% to 75% of these blooms have been found to be toxic. Microcystins (MCYSTs), the predominant toxins of cyanobacterial blooms, are associated with mortality and illness in both animals and humans. Laboratory-controlled experiments studying the effects of different microcystins on the common carp (Cyprinus carpio) have revealed various histopathological alterations. The aim of the present study is to investigate the effect of chronic or subchronic exposure of fish to microcystins under natural environmental conditions by examining the possible histopathological changes associated with a dense cyanobacterial bloom and determining the microcystin contents of fish tissues. Common carps (C. carpio) were caught from Lake Karla (Greece), during a dense cyanobacterial bloom. The concentration of MCYSTs in the fish liver, kidney and muscle tissues was measured by enzyme-linked immunosorbent assay. The pseudogaster contents were analysed, and a histopathological examination was performed using light and electron microscopy. Severe alterations were detected in the liver and the kidney, suggesting that the toxic effects were caused by various pollutants that were particularly associated with microcystins. The histopathological findings are also discussed, taking into consideration the health conditions of the common carp as a commercial fish species. The mechanisms of expansion of the microcystins and the poisoning of aquatic organisms (e.g. fish) are not yet known in the Lake Karla ecosystem. Future research may focus on identifying the changes caused by microcystins and other factors that exert similar effects on fish tissues, as well as on establishing the overall combined effect of all these factors on fish health.