To obtain Pasteurella piscidia determinant gene, a new gene that has a specific base sequence and is useful for reagents for identifying Pasteurella piscidia, a virus infecting young yellowtail, and enables easy and prompt identification of viruses of fish-infecting diseases.

This Pasteurella piscidia determinant gene, which is useful for reagents, such as probes and primers, capable of identifying Pasteurella piscidia, a virus infecting young yellowtail, etc., comprises a gene having the base sequence of the formula or a gene that has a base sequence of the formula in which one or more bases are deleted, replaced or added, and can identify Pasteurella piscidia. This determinant gene is obtained by extracting a plasmid DNA of Pasteurella piscidia KP9038 (FRRM P-15936), digesting the DNA with a restriction enzyme EcoRI and HincII, integrating the obtained fragments of approximately 0.96kbp into a vector, and introducing the vector into Escherichia coil, and recovering the fragments after the proliferation.