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ARS Home » Southeast Area » Stuttgart, Arkansas » Harry K. Dupree Stuttgart National Aquaculture Research Cntr » Research » Publications at this Location » Publication #222957
Title: Laboratory efficacy of oxytetracyline and amoxicillin for the control of Streptococcus iniae infection in tilapia

Author
item Darwish, Ahmed

Submitted to: Annual Eastern Fish Health Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2008
Publication Date: 4/4/2008
Citation: Darwish, A.M. 2008. Laboratory efficacy of oxytetracyline and amoxicillin for the control of Streptococcus iniae infection in tilapia [abstract]. Annual Eastern Fish Health Workshop. p.81.

Interpretive Summary:

Technical Abstract: Streptococcus iniae infection of tilapia is common in different parts of the world including the United States. The infection has caused devastating economic losses and the closure of many tilapia operations. Proper husbandry and health management practices are essential but when a virulent outbreak is in progress antibiotics can be the only viable option to averting catastrophic mortalities. In vitro and in vivo studies were conducted to assess the efficacy of oxytetracycline (OTC) and amoxicillin (AMX) for controlling S. iniae infection. In vitro, minimum-inhibitory-concentration testing of OTC and AMX against multiple S. iniae isolates revealed general sensitivity at concentration ranges of 0.25-0.5 'g/mL and 0.0156-0.5 'g/mL, respectively. In vivo, two separate experiments were conducted to assess the efficacy of OTC and AMX against an experimental S. iniae infection in tilapia; fish were challenged by waterborne exposure to S. iniae (after skin scraping). Each experiment had a nonchallenged nonmedicated group (negative control), a challenged nonmedicated group (positive control) and challenged groups fed different levels of the medicated feed. Oxytetracycline medicated feed was administered 4 to 5 h-post-challenge at concentrations of 25, 50, 75 and 100 mg active ingredient (OTC)/kg of fish body weight (BW)/d for 14 d. Amoxicillin medicated feed was administered 1 d post-challenge at concentrations of 5, 10, 30 and 50 mg active ingredient (AMX)/kg BW/d for 8 d. The OTC at 50, 75 and 100 mg significantly increased the survival of challenged fish to 45, 85 and 98%, respectively, compared to 7% in the positive control. The survival rates of the 75 and 100 mg OTC treatments (85 and 98%, respectively) were significantly higher than the 50 mg treatment (45%). The AMX at 10, 30 and 80 mg significantly increased the survival of S. iniae infected tilapia to 45, 75 and 93.8%, respectively, compared to 3.8% in the positive control. The survival rate was significantly higher in the 80 mg treatment (93.8%) than the 10 mg treatment (45%).