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United States Department of Agriculture

Agricultural Research Service


item Darwish, Ahmed
item Ismaiel, Ed - Ed

Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2003
Publication Date: 12/1/2003
Citation: Darwish, A.M., Ismaiel, A.A. 2003. Laboratory efficacy of amoxicillin for the control of streptococcus iniae infection in hybrid striped (sunshine) bass. Journal of Aquatic Animal Health. 15:209-214.

Interpretive Summary: Streptococcosis is an infectious disease that affects more than 20 species of fish. The disease represents a real threat to the expansion of hybrid striped bass aquaculture due to the economic losses it inflects. 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 hybrid striped bass. Hybrid striped bass fingerlings were experimentally infected by Streptococcus iniae (the causative agent of the disease) and fed different levels of amoxicillin in the diet. Amoxicillin was found to be effective in controlling the infection in hybrid striped bass at all the levels fed. Fish treated with amoxicillin were able to eliminate the infection and had an average survival rate of 95 % compared to infected non treated fish that had a survival rate of 1 %. This information clearly demonstrates the usefulness of amoxicillin as a potential candidate for controlling streptococcosis.

Technical Abstract: Experimental trial was performed to evaluate the efficacy of amoxicillin (AMX) in controlling Streptococcus iniae infection in hybrid striped bass (Morone chrysops female ´ Morone saxatilis male). Minimum-inhibitory concentration studies of AMX against multiple S. iniae isolates showed a sensitivity range of 0.0156 to 0.5 mg/mL. Amoxicillin dose levels tested were 30, 50, 80 and 120 mg active ingredient per kilogram of fish body weight per day. Administration of medicated feed started 1 d after infection by immersion exposure to S. iniae and continued for 8 consecutive days, followed by 15 d post-treatment observation. The AMX increased the survival rate from 1 % in the infected nonmedicated group to an average survival of 95 % in the infected fish groups receiving the four AMX doses with no significant difference among the AMX medicated groups. Survivors of the infection were not detected to be carriers of the bacteria (negative bacterial isolation).

Last Modified: 05/23/2017
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