STUDIES ON THE CHEMICAL CONTROL OF A VIBRIO-CAMPBELLII-LIKE BACTERIUM AFFECTING HATCHERY-REARED PENAEUS-INDICUS LARVAE

Eleven antimicrobial compounds were tested against a Vibrio campbellii-like bacterium for sensitivity. This bacterium showed sensitivity to chloramphenicol and resistance to other antimicrobials. The minimum inhibitory concentrations of chloramphenicol, oxytetracycline and tetracycline were recorded as 5, 150 and 200 ppm, respectively. Chloramphenicol eliminated the population of the V. campbellii-like bacterium in seawater at a concentration of 25 mg/l, whereas oxytetracycline reduced the population of this bacterium to 3.6 x 10(3) cfu/ml after 18 h of incubation at a concentration of 150 mg/l. Significant mortality of early larval stages was observed when larvae were exposed to chloramphenicol and oxytetracycline at the concentrations of 25 and 200 mg/l, respectively. Chloramphenicol significantly reduced the bacterial flora of protozoea and mysis. The optimum exposure time to chloramphenicol for protozoeae and myses to recover from infection caused by the V. campbellii-like bacterium was determined.