Histopathological effects of microcystin-LR, a cyclic peptide toxin from the cyanobacterium (blue-green alga) Microcystis aeruginosa on common carp ( Cyprinus carpio L.)

The toxic effects of microcystin-LR, a cyclic peptide hepatotoxin produced by the cosmopolitan cyano-bacterium Microcystis aeruginosa, were studied by intraperitoneal injections in common carp Cyprinus carpio L. The lowest consistently lethal dose was 550 μg/kg whereas fish injected with doses ranging from 130–300 μg/kg survived the seven day experiment. Histological examination of vital organs (liver, kidney. heart, intestine, spleen and brain) in fish injected with sublethal doses of the toxin, revealed severe liver damage with dissociation of the hepatocytes and hydropic degeneration. In addition, in the kidney the Bowman's capsules of the glomeruli were dilated. In fish injected with a lethal dose of microcystin-LR a total loss of the liver parenchymal architecture and degeneration of the kidney tubuli were observed. The progression of organ damage was studied by electron microscopy of the liver ultrastructure and by blood plasma activity measurements of enzyme indicators. Swollen mitochondria, dissociation of hepatocytes and vesiculation of RER were observed already at 30 min post-injection. Elevated enzyme activities of lactate dehydrogenase (LDH), alanine aminotransferase (ALAT) and aspartate aminotransferase (ASAT) were measured in the plasma of all fish injected with microcystin-LR. The study shows that MC-LR may in fish, in analogy with its extreme hepatotoxic potential in mammals, cause severe liver damage. In addition, the toxin shows in fish a strong impact on elements of the kidney.