In order to detecting VHS virus titer in various tissues in clinical stage of VHS disease, rainbow trout, Oncorhynchus mykiss, were exposed to virus by bath. The experiments were carried out with 140 fish obtained from rainbow trout farm. The fish were divided into two equal groups in 120 Liter tanks containing 70 fish. Group one was considered as control and group two infected by bath challenge with 103 TCID50 ml-1 of a VHS virus strain serologically similar to reference strain F1 with high pathogenicity in rainbow trout. At days 12, 13 and 14 post infection the organs including kidney, spleen, heart, skin, liver, pyloric caeca and brain were sampled from dead fish with appropriate clinical signs of VHS separately. Each sample was placed in vial adding 1 ml transport medium to assess virus titer in various tissues. Results of the study, showed that significant difference between virus loads in various organs (p≤ 0.05). The highest virus titer belongs to heart while it is in minimum amount in the skin. According to the virus quantity the experimental tissues can be divided in three categories, respectively. Heart and kidney performed the highest amount of virus quantities while liver, gill, pyloric caeca and skin showed the lowest with brain and spleen laying in between. These results point out that the significant levels of VHS virus found in rainbow trout tissues are relevant for biosecurity in VHS-free areas mainly when fish are displayed and retained as whole fish.
