Bath efficacy of sodium hypochlorite, oxytetracycline dihydrate and chloramphenicol against bacterial black disease in fairy shrimp Branchinella thailandensis

To control black disease infecting fairy shrimp Branchinella thailandensis, the effects of concentrations and exposure time to three effective antimicrobials, which inhibited the pathogens in vitro, were evaluated. Exposure to sodium hypochlorite (NaOCl) caused a great toxicological response in the shrimp, 100% mortality was observed within 30 min(-2) h at 5-20 mu g mL(-1). For oxytetracycline dihydrate (OTC) and chloramphenicol (CP), short-term exposure to four high concentrations up to 5 h and long-term exposure (12 days) to four low concentrations were used to determine an appropriate method for bath efficacy. Long-term exposure to low concentrations was more toxic than the short-term. Short-term exposure to OTC showed the highest survival rate and CP was considered more toxic. The minimum survival rate of the shrimp exposed to both antibiotics at 250 mu g mL(-1) for 3 h was 83.3%. For determination of the bath efficacy, a short-term exposure (3 h) to OTC and CP was conducted using artificially infected shrimp. Administration of OTC and CP at 250 and 500 mu g mL(-1) resulted in the highest survival rates of 56.7% and 46.7% respectively. This study demonstrated that bath administration with OTC could be an alternative method for the treatment of black disease in fairy shrimp cultivation.