In October 2015, an infectious disease characterized by hemorrhaging from the eyeball, jaw, and operculum, along with neurological symptoms or sudden death with no other clinical symptoms emerged in farms of (Kessler) culture in Ya'an, Sichuan Province, China. A Gram-positive, chain-forming coccus was found in visceral smears. Two bacterial isolates (ZYW151011 and ZYW151012) were isolated from the liver, spleen, and kidney of the diseased pathogenic test, PCR detection of the Streptococcus agalactiae, and sequence analysis of the 16S rRNA gene. Both bacterial isolates were identified as . A 16S rRNA gene sequence analysis by BLAST in GenBank indicated that the two isolates (GenBank accession numbers KU308396 and KU308396) showed high levels of similarity to (99.8%). Drug sensitivity test results showed that both strains were sensitive to ceftriaxone and quinolones, but were not sensitive to doxycycline, florfenicol, and amoxicillin. Serotyping and sequence typing of the two isolates was achieved using capsular polysaccharide serotyping and multilocus sequence typing (MLST), respectively. The serotype of both isolates was pathogenic type Ia. The two isolates were identified as a new sequence type (ZST-1), closely related to ST-261. The allele gene sequence has been submitted to the MLST database under the new allele number 81 (ID, BIGSdb_20151110081850_13025_35759) based on this new variation of in the novel sequence type ZST-1.