This is a report concerning the diseases in artifical salmon propagation programme in Hokkaido. Although the diseases during the artificial propagation of salmons are usually not so frequent as those in fish culture, the preventive and restraint of them are indispensable to the salmon propagation on account of their artificial mass production.
It has been widely known that almost all the diseases of salmon resulted in the mass mortalities are caused by well described microorganisms. Furunclosis caused by Aeromonas salmonicida occurs often in the immature adult fish kept in a holding pond untile they reach maturity. Bacterial kidney disease has now been recongnized in cultured salmon.
Infections with Saprolegnia sp. and Achlya sp. have been usually found in adult fish of salmons holding pond. Although most of the saprolegnoid infections are generally considered to be secondary condition, kokanee salmon, Oncorhynchus nerka var. adonis, has been heavily infected with Saprolegnia shikotsuensis sp. nov. from 1974 to 1978, except 1976.
Gill diseases caused by various bacterial species or protozoa are found frequently in salmon fry. Especially, in chum salmon fry bacterial gill idseases tend to increase recently along with the diffusion of fry feeding.
Among the virus diseases that occur in salmonid in epizootic proportions, so far only IHN is found in masu salmon and kokanee salmon at times, but it is still not recorded in chum salmon fry in Hokkaido.
External protozoan disease caused by Tricodina sp. is usually not so frequent and serious as the bacterial and virus diseases.
