Striped jack nervous necrosis virus (SJNNV), the causative agent of viral nervous necrosis in marine fish, is a member of the family Nodaviridae whose genome consists of two positive-sense RNA molecules encapsidated in a single virion. In this study, the nucleotide sequence of SJNNV RNA1 was determined. The SJNNV RNA1 was 3081 bases long and contained a single ORF encoding 983 aa of approximately 110 kDa. The sequence identities between RNA1 of SJNNV and RNA1 of insect nodaviruses were 28% at the nucleotide and amino acid levels, although the conserved motifs for the RNA-dependent RNA polymerase were located at almost the same positions in the amino acid sequences. The present study, together with our previous work on SJNNV RNA2, suggests that a new genus, Piscinodavirus, should be created in the family Nodaviridae.