Practical Inoculation Site for Experimental Infection of Japanese Flounder Paralichthys olivaceus with Streptococcus parauberis

In experimental infection with Streptococcus parauberis in Japanese flounder Paralichthys olivaceus, we investigated suitable routes of inoculation for a reproduction of natural infection: intraperitoneal injection, intravascular one in tail, intramuscular one into a lateral muscle or erecting and depressing muscles of dorsal fin, and subcutaneous one at a base of dorsal fin or outside preopercular bone. Among these routes, the subcutaneous injection resulted in the challenge-dose-dependent mortality. Disease and histopathological signs of the dead fish were similar to those of spontaneously affected fish. The subcutaneous injection at a base of dorsal fin or outside preopercular bone is a recommended method at a challenge of S. parauberis.