First report on intersex in invasive round goby Neogobius melanostomus from the Baltic Sea (Gulf of Gdańsk, Poland)

SummaryThis study is the first to report the presence of intersex in invasive round goby Neogobius melanostomus inhabiting the Baltic Sea. The discovery was made in the area of two harbours of the Gulf of Gdańsk (Poland). Macro- and microscopic male gonad analysis revealed the presence of female gametes in testes (testis-ova) of single specimens. In addition, a female-like urogenital papilla was observed in one of the intersex fish. These findings might be due to the exposure to estrogenic endocrine disrupting compounds (EDCs) however the occurrence of single intersex individuals as a baseline level in investigated population is also possible. In the future, more comprehensive research in the other areas of the Gulf of Gdańsk needs to be carried out in order to determine the extent and to better understand the cause of the observed phenomenon.