Studies on the sources of luminescent Vibrio harveyi in Penaeus monodon hatcheries
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One of the major problems in the otherwise highly successful Penaeus monodon hatchery industry in the Philippines is the occurrence of luminescent bacterial disease due to Vibrio harveyi. The possible sources of the bacteria were investigated. Eggs within the ovaries of stage III and IV wild-caught and ablated female P. monodon harbour no bacteria. On the other hand, the midgut contents of these spawners, as well as of pond-reared juveniles, contained numerous luminescent bacteria. Plate counts of the exoskeleton from all sampled females revealed that V. harveyi is a minor component of the exoskeleton-associated flora. Scanning electron microscopy of the exoskeleton showed no significant attached populations. The bacterial loads of Chaetoceros calcitrans, a marine diatom, and Artemia salina nauplii were likewise estimated. C. calcitrans did not harbour V. harveyi at any phase of its growth. Twenty-four-hour-old A. salina appeared to have no resident V. harveyi, but its culture water contained small populations of these bacteria. These data show that the main source of the luminescent bacteria is the midgut contents of the mother, which are shed into the water almost simultaneously with the eggs during spawning.