Efeito do extrato bruto da cianobactéria Radiocystis fernandoi em pacu (Piaractus mesopotamicus, Holmberg, 1887)
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Increasing levels of eutrophication in aquatic environments favors the appearance and proliferation of cyanobacteria that can produce toxic compounds and exhibit varying levels of toxicity. Microcystins (MCs) are hepatotoxins that can be produced by different species of cyanobacteria, but which can affect other organs. The objective of the present study was to investigate whether the crude extract of Radiocystis fernandoi strain R28, which contains MC-RR and MC-YR variants and small amounts of other oligopeptides, may present fish toxicity (Piaractus mesopotamicus), compromising the osmoregulatory processes in gills and kidneys, as well as liver function. P. mesopotamicus were injected intraperitoneally (ip) with 100 μg of MC-LR equivalent per kg-1 body weight using 0.5 ml of saline solution (NaCl 0.9%) as vehicle and the gills, kidneys and liver were analyzed 6 and 24 hours after injection using biochemical and morphological biomarkers. The respective controls for each time were i.p. injected with 0.5 mL of saline solution. The gills showed no changes in PP1 and PP2A phosphatase proteins and in the kidneys there was inhibition 6 h after injection. A change in ionic balance occurred. In the gills, Na/K-ATPase (NKA) activity increased after 3 h, decreased after 6 h and did not change after 24 h, the activities of H-ATPase (HA) and carbonic anhydrase (CA) were not altered; there was no change in these enzymes. Chloride cells (CC) decreased 3 h after crude extract injection and showed a tendency to increase in the lamellae after 6 and 24 hours. Several histopathologies such as cell hypertrophy, partial lamella fusion, and lamellar epithelial dislocation and disruption were observed in the gills, but no changes occurred in the kidneys. The histopathological and enzymatic changes in the gills after the injection of crude extract of R. fernandoi and the alteration of Na+plasma show that the substances present in the extract influence the ionic homeostasis in fish. Changes in hepatic and cellular architecture, hyperemia, cellular hypertrophy, cellular atrophy, nuclear alterations and, after 24 hours, the increase of intracellular inclusions together with pycnotic nuclei may be indicative of the inhibition of PP1 and PP2A in the liver of cell death. In addition, alterations in plasma levels of alanine aminotransferases (ALT), aspartate aminotransferases (AST), acid phosphatase (ACP) and alkaline phosphatase (ALP) of liver function as well as changes in bilirubin levels indicate impairment and damage to hepatocyte structure . In conclusion, the results suggest that the crude extract of the R. fernandoi cyanobacteria can compromise the osmoregulatory processes with the alteration of the NKA and chloride cells with consequent alteration in the plasma concentration of ions and present hepatic toxicity compromising the function of the liver and being able to affect the health and survival of fish.