The development of the aerob-mesophilic bacteria on epidermis and peritoneum of 68 barbels was determined at 0, 4 and 8 hours after slaughtering. Therefore, one group of 34 animals was stored at 15.3 degrees C, an other equal one at 21.6 degrees C. A change in germ counts per cm2 could be seen in none of the groups during the first 4 hours. However, unrefrigerated carcasses showed an increase of bacteria up to 5-fold between the 4th and 8th hour, whereas in the refrigerated group no change occurred during that time, too. Rinsing the fish after slaughtering resulted in a decrease of the initial bacterial counts by up to 65.4% and so in significantly lower germ loads at the end of the storage time. These results were confirmed by contaminating 24 rainbow trout with Salmonella Infantis artificially. The frequency of detection did not change in refrigerated fish over 8 hours, while nearly doubling in unrefrigerated ones. Moreover, it could be shown that a Salmonella-concentration of only 30 CFU per 100 ml water was sufficient for contaminating fish in detectable grades. The study leads to the conclusion that the storage of instantly slaughtered fish in a common thermobox with freezing elements is suited for preserving its microbiological status for at least 8 hours. The caging of living fish after capture, which must be regarded critically under the aspect of treating animals in a humane way, seems therefore unnecessary.