Sperm performance limits the reproduction of an invasive fish in novel salinities

Aim: The few fish species able to reproduce across wide osmotic ranges either plastically acclimate sperm performance to, or are locally adapted to, different salinities. The invasive round goby (Neogobius melanostomus) is spreading in Eurasia and the Americas, into both fresh and brackish water. We aim to understand if reproduction in different salinities is affected an ability to acclimate.

Location: Brackish and freshwater systems of northern Europe and the Baltic Sea.

Methods: We cross-exposed round gobies from freshwater and brackish origin to 0 and 16 practical salinity units (PSU), and the fish were given nest boxes to spawn. After four weeks, we measured their sperm performance in both 0 and 16 PSU, fertilization success of each clutch was measured through visual analysis of eggs. Clutches were split and allowed to develop in both 0 and 16 PSU salinity, and reproductive success (zygote development) was measured 20±1 days later. Responses were analyzed using generalized mix...