Efficacy of Sand Filtration and Ultraviolet Irradiation as Seawater Treatment to Prevent Kudoa septempunctata (Myxozoa: Multivalvulida) Infection in Olive Flounder Paralichthys olivaceus

Abstract

Kudoa septempunctata infecting the muscle of the olive flounder Paralichthys olivaceus has been recently demonstrated to cause food poisoning in humans who eat the raw flesh of flounder. In the present study, we assessed the effective treatments of a water supply to prevent K. septempunctata infection in a flounder hatchery where the parasite was enzootic. The prevalence of infection in a positive control fish group exposed to unfiltered seawater was 33% at 3 months post-exposure, whereas no infection was observed in the treated fish groups exposed to sand-filtered seawater, sand- and cartridge (5 μm)-filtered seawater or sand-filtered seawater followed by ultraviolet (UV) irradiation at a dose of 46 mJ/cm². Additionally, treatment with UV irradiation alone was effective for the prevention of K. septempunctata infection. To ensure complete protection from K. septempunctata infection, we recommend double treatments of a water supply with sand filtration and UV irradiation in olive flounder hatcheries.