3.4. Bacterial batch challenge Cumulative mortalities of fish in RAS-C and RAS-O3are shown in Fig. 3. Mortality was clearly higher in RAS-C from the second day of the bacterial challenge. On the fourth day, the mortality o fRAS-C fish was almost twice that of RAS-O3fish. After the fourthday, mortalities in both RAS-O3and RAS-C leveled off. At the end ofthe challenge period, 42% of fish were dead in RAS-C and 18% were dead in RAS-O3.