Selection of brood stock candidates of barfin flounder using an ELISA system with recombinant protein of barfin flounder nervous necrosis virus

Barfin flounder nervous necrosis virus (BFNNV), the causative agent of viral nervous necrosis (VNN) of barfin flounder, is vertically transmitted from spawners to larvae. In the present study, an ELISA with a recombinant protein of BFNNV was performed for the detection of antibodies against BFNNV and applied for the selection of brood fish in order to prevent viral vertical transmissions. Brood stocks were divided into 4 groups based on ELISA antibody titers (less than or equal to 10, 20, 40 and >40), and the BFNNV status of the brood stocks was determined by PCR. BFNNV was detected from the brood fish in the group with an antibody titer of >40 but not from those with titers less than or equal to 10, 20 and 40. The offspring obtained from PCR-negative brood fish pairs in each group of ELISA antibody titers were subsequently reared for observation of VNN occurrence. VNN occurred in juveniles from 2 of 9 pairs of spawners with an antibody titer greater than or equal to 40, but did not occur in spawners with an antibody titer of less than or equal to 10. Therefore, it was concluded that selection of brood fish using both the PCR test and ELISA antibody titers could help prevent vertical transmission of BFNNV in larval production of barfin flounder.