The Ras guanyl nucleotide-releasing protein-3() is a guanyl nucleotide exchange protein thatplays important roles in the occurrence of various diseases when differentially expressed. To explore the genetic composition, tissue expression, and immune response characteristics of cDNA was cloned using rapid-amplification of cDNA ends technology based on the partialtranscriptome data. Amino acid sequence alignment and homology analyses were performed based on the sequencing results. The full-length cDNA was 2756 bp, contained a 2244-bp-long open reading frame, and encoded a protein of 747 amino acids. The amino acid sequence ofwas highly homologous with those of other fish species. We applied quantitative real-time polymerase chain reaction (qRT-PCR) analysis to study the expression patterns of the -infected tissues at different time points with lipopolysaccharide, peptidoglycan (PGN), whole glucan particles, and polyinosinic: polycytidylic acid (poly I:C). The qRT-PCR results showed that . The expression level was highest in ovary, followed by liver, brain, and spleen, but low in blood. V. anguillarum-infected tissues. expression was up regulated 3- and 30-fold in liver and gill, respectively, at 6h compared with that at 0h. expression was downregulated in intestine, spleen, headkidney, and blood 6h after infection with RasGRP3 expression was upregulated after PGN and poly(I:C) stimulation. PGN up regulated expression 13-fold after 24 h compared with that at 0 h, and poly I:C up regulated expression eight-fold after 6 h compared with that at 0 h. These results indicate that the immune response and may play an important role in immune regulation.