RESUMO
Studies of genotoxicity in fish caused by cyanobacterial extracts containing microcystins (MCs) can be useful in determining their carcinogenic risk due to a genotoxic mechanism. An extract of cyanobacterial Microcystis ssp, containing MC-LR and -LA from a bloom collected in a eutrophic lake, showed genotoxicity to Oreochromis niloticus. DNA damage (comet assay) was significantly induced in peripheral erythrocytes with both tested concentrations of 6.90 µg kg(-1) bw and 13.80 µg kg(-1) bw through intraperitoneal injection (ip). There was no micronucleus induction after ip injection at concentrations of 6.90 µg kg(-1) bw and 13.80 µg kg(-1) bw. Body exposure resulted in micronucleus induction and DNA damage only at the highest tested concentrations of 103.72 µg L(-1). Thus, comet assay and ip injection revealed the highest levels of the genotoxicity of MCs. Apoptosis-necrosis test carried out at concentrations of 6.90 µg kg(-1) bw and 13.80 µg kg(-1) bw revealed that at low concentrations more apoptosis than necrosis occurred. At higher concentrations more necrosis than apoptosis occurred.