Body weight and water temperature shape VHSV infection dynamics and shedding in olive flounder (Paralichthys olivaceus).

Smaller fish at colder temperatures shed more VHSV; prioritize juvenile surveillance in winter.

This experimental study evaluated how fish body weight and water temperature interact to influence viral hemorrhagic septicemia virus (VHSV) infection dynamics in olive flounder. Three weight groups (10g, 100g, 200g) were challenged with VHSV at three temperatures (8°C, 13°C, 18°C). Results demonstrated that smaller fish and colder water temperatures (8-13°C) significantly amplified viral burden in spleen tissue, reaching severe infection levels with 100% cytopathic effect. Conversely, 18°C consistently mitigated infection severity across all weight groups. Water and fish viral loads showed positive correlation, with each log increase in spleen viral load increasing shedding odds 3.4-fold. Notably, these effects were pronounced in juvenile fish (10-100g) but absent in larger fish (200g). The findings support temperature- and weight-dependent risk assessment strategies for VHSV management in aquaculture, with particular emphasis on monitoring juvenile cohorts during colder periods.

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