Many viruses induce a strong T cell response that contributes to the elimination of infected cells presenting viral peptides by MHC molecules. The structure and expression of genes encoding molecules homologous to mammalian alphabeta TCRs have been recently characterized in rainbow trout and in several teleost species, but the alphabeta T cell response against pathogens has not been directly demonstrated. To study the modifications of the T cell repertoire during an acute viral infection in rainbow trout, we adapted the immunoscope methodology, which consists of spectratyping the complementarity-determining region 3 length of the TCRbeta chain. We showed that the naive T cell repertoire is polyclonal and highly diverse in the naive rainbow trout. Using viral hemorrhagic septicemia virus (VHSV), which provokes an acute infection in rainbow trout, we identified skewed complementarity-determining region 3 size profiles for several VbetaJbeta combinations, corresponding to T cell clonal expansions during primary and secondary response to VHSV. Both public and private T cell expansions were shown by immunoscope analysis of spleen cells from several infected individuals of a rainbow trout clone sharing the same genetic background. The public response to VHSV consisted of expansion of Vbeta4Jbeta1 T cell, which appeared early during the primary response and was strongly boosted during the secondary response.