Prior to this presentation on preventive measures against fish communicable diseases being theme of this symposium or against fish viral diseases in this subject, the author presents some comments on fish-virus ecology in fish community as the first chapter, subsequently he transfers to the second involving the preventive measures.In the first chapter the author points out that two transmission of vertical and horizontal infection involve in fish viral contagions and the sexual products coming from latently IPN-infected male brood make the vertical transmission spread easily by artificial fertilization with the products which never contain neutralizing antibody to IPNV.In the second he reviews on the virucidal effects of iodine phore, hard water or salt water and a derivative of an ascorbic acid(unpublished)and on the effect of ultraviolet irradiation as well as prophyractic effects to IPN, IHN, VHS by means of artificial active immunity, and on interferon efficacy. He emphasizes that the combined measures with active immunity and an interferon are worthy to be put in an idea as one of the prophyractic measures against viral epizootics occurring at an early stage in the developement of fish like the host of IPN, IHN and others.He stresses that the preventive measures employed can be polytechnic and must impose two significances of controlling the virus in the environmental water for fishes and of inactivating the agent invaded in the animals. The former can be fulfilled with environmental hygienic technology involved using disinfectants or virucidals as the chemical treatment and ultraviolet irradiation as the physical. The latter can be or may be achieved with artificially enhanced fish physiological activity like artificial immunity and artificial interferon induction as well as these combined measures.