Cvetanje cijanobakterija, prisustvo cijanotoksina i njihov uticaj na ribe u pojedinim jezerskim ekosistemima Srbije i Mađarske

In the last several decades, an intense deterioration of water quality followed by subsequent eutrophication is occurring in many freshwater ecosystems due anthropogenic effects. Conditions of highened nutrient concentrations and eutrophication cause intense cyanobacterial proliferations termed cyanobacterial blooming. The aim of this study was to investigate cyanobacterial blooming, potential cyanotoxin production and their effects on fish in four select ecosystems of Serbia and Hungary. Poor water quality and higher concentrations on nitrogen and phosphorus compounds were observed in lakes Ludaš, Fehérvárcsurgó and Kis-Balaton, while the water quality of Lake Balaton was better. Intense cyanobacterial blooms occurred in these three lakes with the numbers of cyanobacterial cells/ml being several million during some months. The most numerous taxa belonged to genera Microcystis, Aphanizomenon and Dolichospermum. Microcystin- and saxitoxin-coding genes were amplified in the biomass of all four lakes indicating a presence of potentially toxin-producing strains. Different microcystin structural variants were detected in lakes Ludaš, Fehérvárcsurgó and Kis-Balaton, while these toxins were not quantified in Lake Balaton. Cylindrospermopsin was not detected in any of the analyzed lakes. Additionally, toxins were not accumulated in fish tissues in any of the analyzed lakes. Fish sampled from lakes Ludaš and Kis-Balaton displayed severe histopathological alterations of liver, kidney and gills, while these alterations were milder in fish from lakes Fehérvárcsurgó and Balaton. Fish sampled from Lake Kiš-Balaton in june of2019. displayed alterations in the activity of detoxication enzymes, as well as lipid peroxidation and alterations in the activity of antioxidant enzymes indication that these fish were under oxidative stress. Results obtained during this study demonstrate intense cyanobacterial blooming in lakes Ludaš, Fehérvárcsurgó and Kis-Balaton, as well as potential danger and negative effects that such blooming can cause in organisms that are in contact with these ecosystems. Therefore, further monitoring, and potentially sanation, of these ecosystems is imperative in the future.