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 different salinities. invasive round goby (Neogobius melanostomus) is spreading in Eurasia and the Americas, into both fresh brackish water. We aim understand if reproduction salinities affected by an ability acclimate. Location Brackish freshwater systems of northern Europe Baltic Sea. Methods cross-exposed gobies origin 0 16 practical salinity units (PSU), were given nest boxes which spawn. After 4 weeks, we measured their PSU; fertilization success each egg clutch was through visual analysis eggs. Clutches split allowed develop PSU salinity, reproductive (zygote development) 20 ± 1 days later. Responses analysed using generalized mixed models. Results a month, showed no plasticity acclimation regardless origin. Sperm velocity highest similar males’ Significantly lower for individuals that reproduced outside despite recurring spawning events all treatment groups. Among fertilized eggs, zygote development eggs parents. Main Conclusions Short-term new does not affect goby. Alternative hypotheses such as local adaption should be further investigated. Limits species’ success, therefore invasion processes, likely dependent on environment-phenotype matches. Fish spawned successfully freshwater, pointing increased risk introducing populations freshwater.