Disinfectant effects of U.V. irradiation were examined on cell suspensions of 5 species of fish pathogenic bacteria, and a punched agar medium disk covered with 10 strains of aquatic fungi and 7 strains of cell free fish pathogenic viruses. 99 .99 % or more of the viable bacterial cells were effected by U.V. treatment of more than 2.2 × 10^3 μW•sec/cm2 U.V. dosage. The hyphae of aquatic fungi showed relatively lower susceptibility to U.V. irradiation, that which inhibited the growth of hyphae was 1.5 - 2.5 × 10^5 μW•sec/cm2. Fish viruses, IHNV, HRV, OMV, CCV and H. salmonis were found to be sensitive to U.V. irradiation, and a 99 % or more infectively decrease (ID99) was 1.0 – 3.0 × 10^3 μW•sec/cm2. Susceptibility of IPNV and CSV were found to be low, ID99 measured 1.0 – 1.5 × 10^5 μW•sec/cm2. The infectivity of IHNV, in virus contaminated river water and IHNV contaminated pond water, measured by the molecular filtration method was 0.56 and 5.6 TCID50/l, respectively U.V. treatment of river water with 10^3 μW•sec/cm2 dosage could prevent an IHN outbreak. Furthermore, U.V. treatment of the hatchery water supply also decreases the visible bacterial counts and fungi infection rates of salmonid eggs.Second Asian Fisheries Forum. 17-22 April 1989. Tokyo, Japan
