Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 30, 2002
Publication Date: September 15, 2002
Citation: DARWISH, A.M., RAWLES, S.D., GRIFFIN, B.R. DOSE TITRATION OF OXYTETRACYCLINE AGAINST STREPTOCOCCUS INIAE INFECTION BLUE TILAPIA, TILAPIA AUREA.. JOURNAL OF AQUATIC ANIMAL HEALTH. 2002. v.14. p.184-190. 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 tilapia 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 oxytetracycline (OTC) as a candidate to control streptococcosis in tilapia. Tilapia fingerlings were experimentally infected by Streptococcus iniae (the causative agent of the disease) and fed different levels of oxytetracycline in the diet. Oxytetracycline was found to be effective in controlling the infection in tilapia. Fish treated with certain OTC level were able to eliminate the infection and had high survival rate. This information clearly demonstrates the usefulness of OTC as a potential candidate for controlling streptococcosis.
Technical Abstract: Experimental trials were performed to evaluate the efficacy of oxytetracycline (OTC) in controlling Streptococcus iniae infection in blue tilapia, Tilapia aurea. Minimum-inhibitory-concentration studies of OTC against several S. iniae isolates indicated general sensitivity at concentration of 0.25-0.5 ?g/mL. Oxytetracycline dose levels tested were 25, 50, 75 and 100 mg active ingredient per kilogram of fish body weight per day. Administration of medicated feed started within few hours after infection by waterborne exposure to S. iniae (after skin scraping) and continued for 14 consecutive days, followed by 21 d post-treatment observation. The 50 mg OTC treatment significantly increased the survival of the infected tilapia from 7 % in the infected non-medicated group to 45 %. The 75 and 100 mg OTC treatments had survival rates (85 and 98 %, respectively) significantly higher than the 50 mg treatment. There was no significant difference among both the 75 and 100 mg treatments and the uninfected non-medicated treatment (100 % survival). Survivors of the 100 mg OTC treatments were not carriers of the infection whereas 10 % of survivors receiving the 75 mg OTC level were carriers.