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United States Department of Agriculture

Agricultural Research Service


item Darwish, Ahmed
item Hobbs, Melissa

Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2004
Publication Date: 6/2/2005
Citation: Darwish, A.M., Hobbs, M.S. 2005. Laboratory efficacy of amoxicillin for the control of Streptococcus iniae infection in blue tilapia. Journal of Aquatic Animal Health. 17:192-202.

Interpretive Summary: Streptococcosis is an infectious disease that affects more than 20 species of fish. The disease causes great economic losses and represents a real danger to cultured warmwater fish, particularly intensively cultured tilapia. In the United States there is currently no approved drug by the Food and Drug Administration (FDA) to control this disease. The objective of this research was to test the effectiveness of amoxicillin as a candidate to control streptococcosis in tilapia. Blue tilapia fingerlings were experimentally infected by Streptococcus iniae (the causative agent of the disease) and fed different levels of amoxicillin in the diet. Fish fed amoxillin in the diet at levels of 10, 30 and 80 mg/kg body weight/day for 12 days had survival rates of 45, 75 and 93.8 %, respectively, whereas infected fish fed diet with no amoxicillin had a survival rate of 3.8 %. The results of this study clearly demonstrated the usefulness of amoxicillin as a potential candidate for controlling streptococcosis in blue tilapia.

Technical Abstract: Experimental feeding trials were performed to evaluate the efficacy of amoxicillin (AMX) in controlling Streptococcus iniae infection in blue tilapia, Oreochromis aureus. Doses of AMX tested were 0, 5, 10, 30 and 80 mg active ingredient per kilogram of fish body weight (BW) per day. Administration of medicated feed started within 22-24 h post challenge by waterborne exposure to S. iniae (after skin scraping) and continued for 12 consecutive days, followed by a 17 d post treatment observation. Oral administration of AMX medicated feed for 12 d at 10, 30 and 80 mg AMX/ BW/d significantly increased (P<0.05) the survival of S. iniae infected tilapia from 3.8 % in 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 there was no significant difference between the 30 and 10 mg treatments (75 and 45 %, respectively). At the conclusion of the experiment no carriers were detected in any challenged group receiving AMX medicated diet while the bacterium was recovered from the nonmedicated challenged survivors of the infection.

Last Modified: 06/27/2017
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