Round gobies are an important part of VHSV genotype IVb ecology in the St. Lawrence River and eastern Lake Ontario

Although viral hemorrhagic septicemia virus (VHSV) is known to affect at least 28 species of Great Lakes fish, round gobies (Neogobius melanostomus) appear to be particularly affected. The first report of VHSV in New York State waters occurred in round gobies and in subsequent surveillance efforts a disproportionately high proportion of round gobies were infected with VHSV compared with other species tested. In this study, we tested the experimental susceptibility of round gobies to infection with VHSV in the laboratory, using naïve and previously exposed fish. Naïve fish were significantly more susceptible than previously exposed fish, however previously exposed fish experienced a mortality of 35% over 45days suggesting that previous exposure did not result in complete protection. Field studies at two sites showed a significant change in prevalence over 10weeks in the spring based on non-lethal fin and gill samples, suggesting that great care must be taken when interpreting prevalence from single sampling efforts during VHSV surveillance. There was no difference in the observed diversity of sequence types of virus from fish that tested positive during times of low or high prevalence, or during a confinement-induced laboratory epidemic. These results show that round gobies are experimentally susceptible to VHSV and that the field prevalence of VHSV in this species can vary greatly within a short period of time; these results also provide a preliminary exploration of the role round gobies may be playing in the dynamics of VHSV in the eastern Great Lakes and St. Lawrence River. •Round gobies are highly experimentally susceptible to VHSV IVb.•Previously exposed round gobies are less susceptible to infection than naïve fish.•Site prevalence of VHSV in round gobies can change significantly over two weeks.•VHSV sequence type diversity does not change with different prevalence levels.