Effectiveness of Early Intervention with Florfenicol on a Streptococcus iniae Infection in Blue Tilapia

A study was performed to assess the efficacy of feeding a florfenicol (FFC)-medicated diet to control experimental Streptococcus iniae infection in blue tilapia Oreochromis aureus. Tested doses of FFC were 0, 5, 10, 15, and 30 mg of active ingredient per kilogram of fish body weight (BW) per day. Fish were subjected to waterborne S. iniae exposure after skin scraping, and administration of medicated feed started at 6 h postchallenge and continued for 10 consecutive days, followed by a 12-d posttreatment observation period. Administration of FFC-medicated feed for 10 d significantly increased (P < 0.05) the survival of S. iniae-infected blue tilapia from 19% in the challenged, nonmedicated positive control group to 94, 96, 99, and 98% in the 5-, 10-, 15-, and 30-mg/kg FFC treatment groups, respectively. The survival rates of the different FFC-medicated treatment groups were not significantly different. At the conclusion of the experiment, no S. iniae carriers were detected in any challenged group receiving the FFC-medicated diet, while the bacterium was recovered from the S. iniae-challenged, nonmedicated survivors of the infection. This study suggests that using FFC at 10 mg/kg BW daily for 10 d is an effective treatment against S. iniae infection in blue tilapia.