봄철 및 가을철에 생산된 넙치 치어의 viral hemorrhagic septicemia virus (VHSV)에 대한 감염성 검토

Abstract

This study investigated whether susceptibility to viral hemorrhagic septicemia (VHS) varies with the production season of juvenile olive flounder (Paralichthys olivaceus) in Korean aquaculture. Since 2021, juveniles produced in spring and autumn were experimentally infected with VHSV under identical water temperature conditions using two viral doses (104.05 TCID50/100μL and 106.05 TCID50/100μL). Cumulative mortality was consistently higher in the spring-produced group at both doses, and high-dose infection resulting in 100% in this group. Although viral load at 1 dpi was higher in the spring-produced juveniles, no significant differences in viral replication or infectivity titers were observed between groups at later infection stages when mortality occurred (p > 0.05). Because experimental and hatchery water temperatures were similar across seasons, temperature alone cannot explain the observed differences in susceptibility. Instead, seasonal factors such as photoperiod, growth rate, and endocrine rhythms may influence host immune responses. In particular, autumn-produced juveniles experience relatively longer photoperiod, and photoperiod-regulated melatonin is known to modulate immune gene expression, stress responses, and disease susceptibility in fish. Overall, the results indicate that VHS susceptibility in juvenile olive flounder varies with production season and associated environmental and physiological conditions, highlighting the importance of considering photoperiod and developmental physiological conditions in hatchery and grow-out management.