Demographic variation of viral hemorrhagic septicemia virus among Round Gobies in the St. Lawrence River

OBJECTIVE: We investigated the demographic dynamics of viral hemorrhagic septicemia virus (VHSV) infections in wild Round Goby Neogobius melanostomus from the nearshore habitats of the upper St. Lawrence River from 2018 to 2022. We examined viral prevalence and titers between Round Goby sexes and age-classes to identify how demography correlates with prevalence and amplification of this pathogen within this host species. METHODS: Reverse-transcription quantitative polymerase chain reaction was used to detect and quantify viral N-gene genetic material in pooled organ (i.e., liver, kidney, spleen) and brain tissues of wild Round Gobies that were collected from the upper St. Lawrence River. Age and sex were assigned to each individual to elucidate how patterns of infection prevalence and amplification vary depending on demography within this host species. RESULT: Viral hemorrhagic septicemia virus was detected by reverse-transcription quantitative polymerase chain reaction in 49.62% of the sampled Round Gobies, with significant variation in prevalence and titers observed across demographic groups. Sex-based VHSV prevalence was 15.87% in females and 55.95% in males, and infected fish of both sexes contained similar median viral titers. Age-based prevalence increased with age, ranging from 14.29% in age-1 fish to 68.35% in age-4 fish, whereas viral titers were highest in age-2 fish and decreased with age thereafter. CONCLUSION: Round Gobies exhibit a high prevalence (49.62%) of VHSV infections. However, the pathogen is distributed unevenly among demographics within this species. Both sex and age interact with the infection status of an individual.