Streptococcus Infections in Cultured Pond Loach Paramisgurnus dabryanus in China

In 2017, high mortalities were observed in cultured pond loach Paramisgurnus dabryanus in Tianjin, China. The symptoms observed in the moribund loach included hemorrhage on the body surface and head, exophthalmos, and erratic swimming around the water surface. Two different Gram-positive bacteria were isolated from the diseased loach in two different fish farms. They were identified as Streptococcus dysgalactiae and Streptococcus agalactiae, using 16S rRNA gene sequencing and biochemical characterization. The median lethal doses of the bacterial strains in the loach were 3.2 x 10(5) and 5.0 x 10(5) CFU/fish, respectively.