Susceptibility of Soiny Mullet (Liza Haematocheila) to Streptococcus Dysgalactiae and Physiological Response to Formalin Inactivated S. Dysgalactiae

Streptococcosis caused great lost in intensive aquaculture in China every year. The Streptococcus dysgalactiae, one of the main pathogen of streptococcosis in cultured fish in China, caused high mortality of Soiny Mullet (Liza hematocheila) with typical symptom after intraperitoneal injection. The semi-lethal dose of S. dysgalactiae to mullet was 5.4×106 CFU. The antigen against S. dysgalactiae was prepared by formalin inactivated S. dysgalactiae. After intraperitoneal injection of the antigen, the survival rate of fish infected with S. dysgalactiae was significantly increased. At the same time, the splenic and hepatic lysozymes of mullet were also significantly increased. The splenic and hepatic ALP were decreased from 1 day to 3 day and back to normal level at 7 days after vaccine injection. All these data strongly suggested that the formalin-inactivated S. dysgalactiae is an effective strategy to protect mullet against S. dysgalactiae.