Standardization of Dose and Delivery of Oxytetracycline against Streptococcus agalactiae Infection in Genetically Improved Farmed Tilapia (GIFT)

Background: Tilapia (Oreochromis niloticus) is one of the most important aquaculture species in India. Streptococcus agalactiae is a highly debilitating pathogen of farmed tilapia. In this study, oxytetracycline (OTC) dose and delivery were standardized against S. agalactiae infection in genetically improved farmed tilapia (GIFT) and pharmacokinetics after oral administration was evaluated. Methods: LD50 value of S. agalactiae was found to be 6.2×106 CFU/fish. Two methods of drug delivery were investigated at three different doses of 50, 70 and 90 mg/kg against the S. agalactiae infection. Pharmacokinetics of OTC was studied after per os administration of 100 mg/kg body weight per day and analysing the residues in kidney, liver and muscle at different time intervals. Result: Per os delivery of OTC 90 mg/kg controlled S. agalactiae infection and the withdrawal time of OTC to fall below MRL of 0.05 µg/g at 30°C was 21 days in kidney and liver and 14 days in muscle. The study indicated that the S. agalactiae infection in tilapia could be controlled by OTC and fish can be marketed after providing a withdrawal period of 14 days.