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ARS Home » Southeast Area » Stoneville, Mississippi » Warmwater Aquaculture Research Unit » Research » Publications at this Location » Publication #270451
Title: Determination of florfenicol dose rate in feed for control of mortality in nile tilapia Oreochromis nilotica infected with streptococcus iniae

Author
item GAUNT, P - Mississippi State University
item ENDRIS, R - Schering-Plough Research
item MCGINNIS, A - Mississippi State University
item BAUMGARTNER, W - Mississippi State University
item CAMUS, A - Mississippi State University
item STEADMAN, J - Mississippi State University
item SWEENEY, D - Schering-Plough Research
item SUN, F - Schering-Plough Research

Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2010
Publication Date: 7/28/2010
Citation: Gaunt, P., Endris, R., Mcginnis, A., Baumgartner, W., Camus, A., Steadman, J., Sweeney, D., Sun, F. 2010. Determination of florfenicol dose rate in feed for control of mortality in nile tilapia Oreochromis nilotica infected with streptococcus iniae. Journal of Aquatic Animal Health. 22:158-166.

Interpretive Summary: Three different doses 5, 10 and 15 mg/kg of body weight were used to determine the dosage of florfenicol in feed that is required to control Streptococcus iniae-associated mortality in Nile tilapia Oreochromis niloticus. Based on these results, the 10 and 15 mg/kg body weight doses were then utilized for a dose confirmation study. These studies show that Florfenicol was palatable, safe, and efficacious for control of Nile tilapia mortality due to S. iniae infection.

Technical Abstract: A dose titration study was conducted to determine the dosage of florfenicol (FFC) in feed to control Streptococcus iniae-associated mortality in Nile tilapia Oreochromis niloticus. Six tanks were assigned to each of five treatments: (1) not challenged with S. iniae and fed unmedicated feed; (2) challenged with S. iniae by injection and fed unmedicated feed; (3) challenged with S. iniae and given FFC at 5 mg/kg of body weight (bw) in medicated feed; (4) challenged with S. iniae and given 10 mg FFC/kg bw; and (5) challenged with S. iniae and given 15 mg FFC/kg bw. Treatment was initiated the day after inoculation, and feed was administered for 10 d. Cumulative mortality was 0% in the unchallenged, untreated group; 35.8 + 4.4% (mean SE) in the challenged, unmedicated group; 19.2 + 2.7% in the 5-mg/kg treated group, 12.5 + 3.8% in the 10-mg/kg group, and 2.5 + 1.1% in the 15-mg/kg group. The cumulative mortality was significantly less in each challenged, FFC-treated group than in the challenged, unmedicated controls (5 mg/kg: P = 0.0156; 10 mg/kg: P = 0.0007; 15 mg/kg: P = 0.0001). The efficacy of the 10- and 15-mg/kg FFC dosages was studied in a separate dose confirmation study. Fish in all tanks were injected with S. iniae. At 4 h postinoculation, 10 tanks were assigned to each of three feed treatments: (1) unmedicated feed; (2) 10 mg FFC/kg bw; and (3) 15 mg FFC/kg bw. Cumulative mortality was 20.5 + 2.0% in the challenged, unmedicated group; 11.0 + 2.1% in the 10-mg/kg group; and 5.5 + 2.4% in the 15-mg/kg group. Mortality was significantly less in the medicated groups than in the challenged, unmedicated control group (10 mg/kg: P = 0.0270; 15 mg/kg: P = 0.0007). Fish in both studies were necropsied, cultured for bacteria, and examined for gross lesions. The minimum inhibitory concentration of FFC against S. iniae in both studies ranged from 0.5 to 1.0 µg/mL. Florfenicol was palatable, safe, and efficacious for control of Nile tilapia mortality due to S. iniae infection.