Costiosis is a dangerous invasion disease of baby fishes growing at fish-farming establishments, fish-factories, spawn-growing and other types of establishments. This fish disease is particularly dangerous to salmonides and carp species. The document consists of 5 Secs. Section 1 lays down general provisions. Section 2 regards epizootology. Section 3 regards clinical symptoms. Section 4 regards diagnosis. Section 5 specifies arrangements for combating the afore-mentioned disease.