Experimental Streptococcus iniae infection in Japanese flounder Paralichthys olivaceus

The capability of Streptococcus iniae to cause disease in Japanese flounder was investigated by oral and bath (30 min) challenges with low, medium and high inoculation doses. Only with the highest inoculation dose, 9.9 x 10(7) CFU/100 g body weight, the oral challenge induced deaths. in the bath challenge deaths were induced even at the lowest inoculation dose, 2.9x10(3) CFU/mL water. Hemorrhagic lesions on the fins were observed in dead fish challenged by both methods. It is suspected that S. iniae entered through the body surface such as abrasive sites of the fins to cause disease.