Effect of blue light emitting diode on viral hemorrhagic septicemia in olive flounder (Paralichthys olivaceus)

Although there are several studies showing antimicrobial activity of blue light emitting diode (LED) light, studies on the virucidal activity of LED are lacking. Therefore, the objective of this study was to investigate the effect of 405-nm LED light on viral hemorrhagic septicemia (VHS) in olive flounder (Paralichthys olivaceus). In vitro virucidal activity of 405-nm LED light was measured using 5.8 and 5.0 log PFU·mL−1 of VHS virus (VHSV) suspended in L-15 medium and fish skin mucus, respectively. In vivo experiment was performed to assess the efficacy of 405-nm LED light at different intensities (10, 20, 30, and 40 μmol∙m−2∙s−1; called 405–10, 405–20, 405–30, and 405–40, respectively) on olive flounder (average weight = 19 ± 4 g or 1.4 ± 0.5 g) artificially challenged with VHSV by both injection and/or immersion methods. Growth performance, survival rate, and expression levels of immune−/stress-related genes were measured to identify possible adverse effects of 405-nm LED light on fish. As a result, illumination with 405-nm LED light inactivated VHSV in a light intensity-dependent manner. Viral concentrations in rearing water and fish skin mucus of 405-nm LED light exposed groups were significantly lower than those of the control groups. Survival rates of cohabitant fish (19 ± 4 g) in the 405–40 group (100% and 87.5% for two replicates) were higher than those in each control group (62.5% and 50% for two replicates). Survival rate of fish (1.4 ± 0.5 g) in the 405–20 group (97%) was significantly higher than that in the control group (78%). However, some fish (1.4 ± 0.5 g) in the 405–30 and 405–40 groups were killed regardless of VHS infection. There were no significant differences between 405-nm LED light-exposed and control groups in growth performance, survival rate, or expression levels of immune−/stress-related genes in fish (average weight = 34.3 ± 4 g or 2.4 ± 0.4 g). In this study, illumination with 405-nm LED light at intensities of 20–40 μmol·m−2·s−1 can inactivate VHSV in rearing water and fish skin mucus, and improve survival rates of fish (larger than 2.5 g) from VHS. This is the first study to demonstrate that blue LED light can be applied to control viral diseases in the aquaculture industry.