Oocyte hydration in round goby Neogobius melanostomus from the Gulf of Gdańsk: another invasive strategy?

The round goby (Neogobius melanostomus) is one of the most abundant non-native species in the Gulf of Gdańsk that use various strategies to increase fecundity and achieve invasive success. Oocyte hydration appears to be a specific osmotic adaptation of round goby's gametes for successful fertilization and hatching. The aim of this study was to demonstrate details of oocyte final maturation and hydration during the spawning-capable phase in round goby and also compare various indices such as 17β-estradiol (E2), hepatosomatic index (HSI) and gonadosomatic index (GSI) among oocyte final maturation stages. E2 fluctuated according to the development of oocyte batches. HSI did not show significant differences throughout the oocyte maturation. GSI was an inaccurate estimator of oocyte maturation in round goby. This study, for the first time, shows that hydration does accompany oocyte final maturation in this species. These findings are important to the cognition of biology and the adaptive strategies of this invasive species to environmental factors and can be essential components of the protection and preservation of native living resources in the Gulf of Gdańsk.