Mass mortality of Penaeus monodon larvae due to antibiotic-resistant Vibrio harveyi infection

The cause of mass mortality in Penaeus monodon larvae in a hatchery was investigated. Antibiotic-resistant Vibrio harveyi could be isolated from all the infected larvae. These bacteria were absent in healthy eggs and nauplii. Although the intake seawater had V. harveyi, these strains were sensitive to antibiotics. The results suggest that antibiotic-resistant V. harveyi had been colonising larval tanks. The isolates from moribund larvae showed much lower LD 50 values than isolates from natural seawater, thus indicating their higher virulence.