Abstract: Zebrafish (Danio rerio) is a new infection model for studying mammal pathogens. 1 005 80-day-old AB line inbred zebrafish were grouped and infected intraperitoneally with 8 highly virulent strains for pigs（mrp+ef+）. The 50% lethal dose(LD50) were in the range of 5.36×103cfu to 5.01×104 cfu1 at 96 h. The SS2 strains which highly virulent for pigs also caused high morbidity and mortality in zebrafish. Acute septicemia were observed in inoculated fish. The bacteria inoculated could be reisolated from the organs of the fish. 1 strain avirulent for pigs（mrp - ef -）was also inoculated but not lethal for fish, and its LD50 was >106 cfu. There is significant difference between the LD50 of SS2 virulent strains and avirulent one(p<0.01). It concludes that zebrafish will be useful for further research of SS2 infection as an new animal model.

Key words: zebrafish(Danio rerio), Streptococcus suis serotype 2(SS2), 50% lethal dose