CP primer was designed according to the sequences of NNV coat protein gene in orange-spotted grouper for virus-free testing(Table 1). Other primers were designed to implement the qRT-PCR analysis (Table 1). Expressions levels of six selected genes weredetected. qRT-PCR was conducted on a 7500 Real-time PCR system (Applied Biosystems, USA) using a SYBRR premix ExTaq™Kit (TaKaRa). The reaction carried out without the template was used as blank control. All samples were performed in triplicate wells, and cycling conditions were as follows: 10 s at 95 C, followed by 40 cycles consisting of 5 s at 95C and 34 s at 60C. Expression ofbactin was used as the internal control for the all gene expressionanalysis. Dissociation curve analysis was performed after thermocycling to determine whether a specific-sized single amplicon was amplified. The gene expressions were determined via the 2 △△CT method. Significant differences were accepted at P