抄録
Efficacy of josamycin (JM) against experimental streptococcal infection in cultured yellowtail was evaluated. Two procedures were used in this experiment. One was bioautographic technique to confirm efficacy of JM in vivo and the other was a practical study to establish the effective dose against experimentally infected yellowtail. JM medicated feed was orally adiministered in each study. Experimental infection was performed by intramuscular injection in the bioautographic study and intraperitoneal injection in the clinical study. In the bioautographic study, JM dis-played in vivo antimicrobial activity. Fishes administered with 25mg/kg of JM excluded pathogen in the muscle after 6 hours. In the practical study, doses of 20mg/kg/day for 5 days and 30mg/kg/day for 3 days were effective against yellowtail infected with 5.8×108cfu/fish pathogen, which is the infeetive dose to kill 90% of the infected yellowtail in 7 days. However, in the experimental injection, the bacterial concentration influenced the JM therapeutic ability. Effective dose depended on the disease condition of yellowtail. The results suggest possibility to be able to control the streptococcicosis of naturally infected yellowtail.
