, 2010). The phenomenon has been confirmed by Bowley et al. (2010) who PLX3397 mouse had reported 10% of intersex at the same site and found individuals with testis-ova at other contaminated sites of the Harbour. In most of Canadian intersex oocytes were in previtellogenic or vacuolization stages. Whereas, single individuals, from the most contaminated site, showed advanced stages of oocytes development, i.e. late vitellogenic ova ( Bowley et al., 2010 and Marentette et al., 2010) and some of them did not show development of seminiferous lobules ( Marentette et al., 2010). In both studies feminization of urogenital papilla has been shown to be a useful

indicator of exposure to EDCs as it was reported only in males CH5424802 mw collected at contaminated sites, while at less polluted and cleaner sites, chosen as reference sites, no urogenital papilla changes nor intersex in males were observed. Since PAHs and PCBs were the major contaminants in sediments at sites, where endocrine disruptions in N. melanostomus were identified, they are thought to be one of the most likely agents responsible for the observed disruptions ( Bowley et al., 2010 and Marentette et al., 2010). In the Baltic Sea, as particularly susceptible

to develop intersex in contaminated environment turned out to be Z. viviparus, which since over a decade has been used in research concerning the impact of EDCs in coastal waters of such countries as Germany, Denmark or Sweden ( Förlin, 2012, Gercken and Sordyl, 2002, Gercken and Sundt, 2007 and Strand et al., 2009). Nevertheless, there were no reports or studies concerning the presence of intersex in Z. viviparus, nor in any other fish species, in the Gulf of Gdańsk. If more comprehensive research indicated that the phenomenon

of intersex in N. melanostomus from the Gulf of Gdańsk is a response to EDCs, N. melanostomus could be suggested as a sentinel species in endocrine disruption Aurora Kinase research, not only in the Gulf but also in other regions of the Baltic Sea invaded by this species. In conclusion, this is the first report of intersex in the invasive N. melanostomus from the Baltic Sea as well as intersex fish in Polish coastal waters. The occurrence of intersex individuals and feminization of secondary sexual characteristics might indicate that N. melanostomus inhabiting coastal waters of the Gulf of Gdańsk was exposed to estrogenic EDCs. However, as only two stations were studied and intersex was observed in single individuals, which might suggest occurrence of spontaneous intersex, an extended study need to be carried out in order to determine the range of the occurrence and the baseline levels of N. melanostomus intersex in the Gulf. Investigations are also necessary to better characterize possible endocrine disrupters at the investigated stations and other areas of the Gulf of Gdańsk. Moreover, if it is shown that the occurrence of intersex is the result of exposure to EDCs, N.