Mast cell proteases play an important role in the regulation of the immune response. We identified the
cDNA of the mast cell protease 8 (MCP-8) gene and analyzed its genomic structure in tilapia. The ORF of
the MCP-8 was 768 bp, encoding 255 amino acids. Quantitative real-time PCR revealed that the MCP-8
gene was expressed predominantly in spleen, moderately in liver, blood, brain, gill, intestine, skin, and
weakly expressed in kidney, muscle and eye. After a challenge with Streptococcus agalactiae, the gene was
induced significantly (p < 0.05) in intestine, kidney, spleen and liver. Furthermore, we identified five
single nucleotide polymorphisms (SNPs) in the MCP-8 gene and found that three SNPs were significantly
associated (p < 0.05) with resistance against S. agalactiae. However, we found no association between
four SNPs and growth traits (p > 0.05). These results suggest that the MCP-8 gene play an important role
in the resistance to S. agalactiae in tilapia. The SNP markers in the MCP-8 gene associated with the
resistance to the bacterial pathogen may facilitate selection of tilapia resistant to the bacterial disease.