Tilapia is a group of cultured teleost fishes whose production is threatened by some diseases. Identification
of DNA markers associated with disease resistance in candidate genes may facilitate to accelerate
the selection of disease resistance. The gene encoding a duodenase, which can trigger immune response,
has not been studied in fish. We characterized the cDNA of duodenase-1 gene of hybrid tilapia. Its ORF is
759 bp, encoding a serine protease of 252 amino acids. This gene consisted of five exons and four introns.
Its expression was detected in all 10 tissues examined, and it was highly expressed in the intestine and
kidney. After a challenge with the bacterial pathogen, Streptococcus agalactiae, its expression was upregulated
significantly in the intestine, liver and spleen. We identified seven SNPs in the gene and
found that four of them were significantly associated with the resistance to S. agalactiae (P < 0.05). The
CGTCC haplotype, CAGTC/CGGTC and CGTCC/CGTCC diplotype were significantly associated with the
resistance to S. agalactiae (P ¼ 0.00, 0.04 and < 0.0001, respectively). In addition, one SNP was associated
significantly with growth traits (P < 0.05). These findings suggest that the duodenase-1 gene plays an
important role in the resistance to S. agalactiae in tilapia. The SNP markers in the duodenase-1 gene
associated with resistance to the bacterial pathogen, may facilitate the selection of tilapia resistant to the
bacterial disease.