Fish grown in contaminated ponds can be exposed to a variety of human pathogenic microorganisms which may accumulate in its tissues. This study was conducted in order to examine the efficiency of changing the water, in the holding tanks, to reduce the level of microorganisms in various fish tissues. Fish contamination was accomplished by seeding 109, 10111010cfu or pfu ml#x2010;1of E.coli, MS2 coliphage and poliovirus 1, respectively, into 1001 of water. These microorganisms were tested in the skin, muscle, liver, spleen and the digestive tract (DT). A single inoculation of the test microorganisms was followed by 3#x2013;24 water changes (tank volumes) and compared with self#x2010;purification (control) experiments without changing the water. The highest levels of microorganisms were found in the DT, 6 h after inoculation for E.coli and 12 h after inoculation for MS2 and poliovirus 1. Lower levels of the microorganisms were found in the spleen, liver and on the skin and none were detected in the muscle. In the decontamination experiments, no microorganisms were detected in the DT 5#x2013;6 days after inoculation, as compared to 11#x2013;21 days in the control experiments. The results of this study indicate that faster decontamination of fish is achieved by repeated changing of the water in the holding tanks and this may lower the risk of disease transmission by fish handling or consumption.
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