ABSTRACT
Micronuclei are formed by the condensation of acentric chromosomal fragments or whole chromosomes not included in the main nuclei following anaphase (Al-Sabti and Metcalfe 1995). They appear as a result of both chromosome breakage and spindle dysfunction. An increase in the frequency of micronucleated cells can arise from chromosomal and genomic damage caused by clastogens or spindle poisons (Mersch et al. 1996). Micronuclei assay presents several advantages for the study of fi sh. Micronuclei can be quantifi ed using blood smears, as teleost erythrocytes are nucleated. Counting micronuclei in erythrocytes is easier than the analysis of chromosomal aberrations in metaphase plates. Micronucleus assay in vitro or in vivo techniques have been developed for use with fi sh. Several tissues were
used to examine the frequency of micronucleated cells in fi sh captured from contaminated sites or in fi sh exposed to contaminants in vivo. Cephalic kidney cells (Rodriguez-Cea et al. 2003), gill cells (Hayashi et al. 1998; Takai et al. 2004; Bolognesi et al. 2006), hepatic tissue cells (Williams and Metcalfe 1992; Rao et al. 1997; Arcand-Hoy and Metcalfe 2000; Pietrapiana et al. 2002; Çavas et al. 2005); fi n cells (Arkhipchuk and Garanko 2005) and embryonic cells (Hayashi et al. 1998) have been used in fi sh micronucleus assay. However erythrocytes are the most commonly used for micronucleus assay in fi sh to date. This is partly because fi sh erythrocytes are nucleated and are easy to obtain and easy to spread as a thin fi lm of cells for examination by microscope. The use of erythrocytes dispenses the need for cell separation. Additionally, there is no need to sacrifi ce the animal to obtain a small blood sample to make a smear. Blood smear staining is simple and the procedures for analysing blood cell micronuclei and associated erythrocyte nuclear abnormality are well established. In addition the high mitotic rate of hematopoietic tissue provides a rapid response to exposure (Bolognesi et al. 2006).
