Abstract

Objective: To assess the efficacy of feeds containing approved antibiotics, viz., oxytetracycline (OTC) or potentiated sulphonamide [(sulphamethoxazole-trimethoprim) SMZ-TMP] at 1 g, 2 g, 3 g and 4 g of respective antibiotics/kg feed at 2% body weight ration in preventing the Aeromonas hydrophila (A. hydrophila) infection in Oreochromis niloticus. Methods: Commercial pellet feed was top dressed with respective antibiotics using 5 mL vegetable oil as a binder. Fish were injected intramuscularly with A. hydrophila at ≈ 6.0 × 107–8.6 × 107 CFU/fish, and fed subsequently with OTC and SMZ-TMP feeds for 10 and 5 days, respectively. Fish mortalities were recorded during the pre-treatment, treatment and posttreatment periods. Results: Highest mortalities (7.42%–8.33%) were observed in challenged and untreated fish. The mortalities observed in fish fed with OTC or SMZ-TMP were 0%–6.66% with decreasing concentrations of antibiotics from 4 to 1 g/kg feed. Significant differences existed in the mortalities among fish fed with different doses of antibiotics (P < 0.05). The relative percent survival values were 20, 40, 40 and 60 for 1 g, 2 g, 3 g and 4 g OTC/kg feed groups, respectively; while in SMZ-TMP fed fish, the respective relative percent survival values were 10, 100, 100, and 100. Conclusions: The fish fed with feed containing 2 g antibiotic/kg at 2% body weight was the lowest concentration that recorded significantly lower mortality (P < 0.05), which could be the treatment of choice for the control of A. hydrophila in Oreochromis niloticus in tropical condition.

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