2.3. Comet assay The comet assay with peripheral blood (erythrocytes; ECA) wasperformed according to Speit and Hartmann [35], modified byCestariby Cestari et al. [9] and Ferraro et al. [14]. For the gill (GCA) and liver(LCA) comet assay, the organs were mechanically homogenized(homogenizer Tecnal-TE-103) at 1500 rpm [31]. Ten microlitersaliquot was taken from each diluted sample and embedded in120 L of low- melting-point agarose (0.5%, Invitrogen). The fol-lowing steps were conducted according to Speit and Hartmann[35].One hundred nucleoids were analyzed for each organ and bloodin each fish according to the visual classification based on themigration of DNA fragments from the nucleus. The results were cat-egorized into classes according to [10]: class 0 (no visible damage),class 1 (little damage), class 2 (medium damage), class 3 (extensivedam- age) and 4 (maximally damaged). The score was calculatedby multiplying the number of nuclei found in a class times the classnumber.