Two monoclonal antibodies were produced against the nucleoproteins of two strains of infectious hematopoietic necrosis virus (IHNV), One antibody, 1NDW14D, obtained by immunizing BALB/c mice with the nucleoprotein from Dworshak IHNV strain DW2, universally recognized IHNV in tests of direct and indirect fluorescence. The second antibody, 2NH105B, obtained by immunization with the nucleoprotein from an IHNV strain isolated from rainbow trout Oncorhynchus mykiss (formerly Salmo gairdneri) in the Hagerman Valley, Idaho, recognized biochemical type-2 IHNV. Both antibodies, 1NDW14D and 2NH105B, when conjugated with fluorescein, can be used in a direct fluorescence test that is more rapid than the previous methods of detecting the virus.