ABSTRACT. In the last few years, monitoring the health of aquatic environments subject to the impact of several human activities has led to the adoption of Teleosts as indicators of environmental changes. Fish are excellent bioindicators of aquatic ecosystems due to their high sensitivity to changes. It has been widely shown that exposure to genotoxic agents causes several alterations and damages at different levels of structural complexity and that micronucleous (MN) and nuclear abnormalities (NA) are the final expression of molecular damage induced by genotoxic agents, demonstrating their usefulness as indicators of genotoxic damage. Compared with other cytogenetic methods, the MN test is the most widely used test for aquatic species as it does not involve cell cultures, it is independent from the number of chromosomes of the species, it is a fast and easy procedure and the identification of micronucleous at the microscope is quite simple. This study was aimed to assess the damage caused by genotoxic agents in aquatic environments, based on the presence of micronucleous and nuclear abnormalities in erythrocytes of the blenny Parablennius sanguinolentus (Pallas, 1814), collected in two sites along the eastern coast of Sicily (Italy). Such a species was considered as a valid bioindicator due to its biological features and its occurrence in the sites object of this study.