Tributyltin exposure increases mortality of nodavirus infected Japanese medaka Oryzias latipes larvae

We investigated the effect of combined exposure to nodavirus infection and TBT on medaka (Oryzias latipes). Medaka larvae were infected by immersion in medium containing nodavirus at titers of 102.5, 103.5, or 104.5 TCID50/mL. Infected fish then were exposed to TBT at 0, 0.17, 0.52, 1.6, or 4.7 μg/L. Of the 12 groups exposed to both stressors, the mortalities of 6 (102.5 TCID50/mL + 0.52, 1.6, or 4.7 μg/L, 103.5 TCID50/mL + 4.7 μg/L and 104.5 TCID50/mL + 1.6 or 4.7 μg/L) were significantly higher than that of each TBT control. Specifically, mortality was 46 ± 5.5% in the group exposed to both 102.5 TCID50/mL virus and 0.52 μg/L TBT, which represent the lowest observed effective dose and concentration, respectively, among the 6 groups with increased mortalities. Our results suggest that combined exposure to both stressors suppresses antiviral mechanisms in the fish, thus increasing mortality.