The aim of this paper was to assess the biological damages in fish caused by various mutagenic agents present in polluted waters of Aliaga Bay. For this purpose, micronuclei (MN) test was performed using peripheral erythrocytes and gill cells of different fish specimens caught from both polluted and relatively clean sites from Aliaga Bay (Turkey). Micronuclei tests is a system of mutagenicity testing used for determining changes in DNA fragments such as micronuclei in the cytoplasm of interphase cells caused by the pollution and chemicals in the environment. Thus, it was attempted to determine whether pollution affected the erythrocytes and gills of fish living in Aliaga Bay at the level of DNA by the means of micronuclei (MN) test. According to the results of present study, frequency of MN was found at high level in polluted site. In conclusion, this study indicates that the micronuclei test gives sensitive results in monitoring the pollution, especially the pollution of harbor, and thus it might be used as standard method in regularly monitoring pollution of coastal ecosystem. (C) 2015 Elsevier Ltd. All rights reserved.