Laboratory Efficacy of Amoxicillin for the Control of Streptococcus iniae Infection in Blue Tilapia

Abstract

AbstractExperimental feeding trials were performed to evaluate the efficacy of amoxicillin (AMX) in controlling Streptococcus iniae infection in blue tilapia Oreochromis aureus. The doses of AMX active ingredient tested were 0, 5, 10, 30, and 80 mg/kg of fish body weight (BW) per day. Administration of medicated feed started within 22–24 h postchallenge by waterborne exposure to S. iniae (after skin scraping) and continued for 12 consecutive days, followed by a 17‐d posttreatment observation. Oral administration of AMX‐medicated feed for 12 d at a daily rate of 10, 30, and 80 mg/kg BW significantly increased the survival of S. iniae−infected tilapia from 3.8% in the challenged, nonmedicated positive control to 45, 75, and 93.8%, respectively. The survival rate was significantly higher in the 80‐mg treatment (93.75%) than the 10‐mg treatment (45%) but did not differ significantly between the 10‐mg (45%) and 30‐mg (75%) treatments. At the conclusion of the experiment, no carriers were detected in any challenged group receiving AMX‐medicated diet, whereas the bacterium was recovered from the nonmedicated, challenged survivors of the infection.