Determination of the Reproductive Status of the Female Round Goby Neogobius melanostomus (Pallas, 1814) in Southwestern Lake Michigan

The successful invasion of the round goby, Neogobius melanostomus (Pallas, 1814), in European and North American water ecosystems is assisted by its reproductive strategy, including high fecundity, multiple spawning events over an extended spawning season, and male parental care of offspring. In this study, we investigated female spawning effort and the determination of their reproductive status. The analysis was based on 552 females caught from May to September in Jackson Harbor (JH) and Waukegan Harbor (WH) in southwestern Lake Michigan (USA). The total length of females ranged from 62.6 to 160.0 mm, and the weight was between 3.47 and 59.8 g. Significantly different maximum mean values of the gonadosomatic index (GSI) in both localities were noted in early June (8.62% for JH) and in mid-June (7.82% for WH), associated with differing thermal regimes. Fecundity exhibited a significant linear relationship with the total length of females at both sites (Jackson Harbor, p < 0.0001, R2 = 0.5861; Waukegan Harbor, p < 0.0001, R2 = 0.6278) and with the total mass of fish (Jackson Harbor, p < 0.0001, R2 = 0.6614; Waukegan Harbor, p < 0.0001, R2 = 0.6327). Histological examination of ovaries showed that the spawning season of the round goby in southwestern Lake Michigan is prolonged from May to late June. The monthly distribution of the different sexual maturity stages and the frequency distribution of oocyte diameter revealed that this species is a batch spawner. The results expand the current knowledge of reproductive biology and physiology of the round goby.