Abstract
Yellowtail Seriola quinqueradiata were experimentally infected with Enterococcus seriolicida in order to investigate the effect of dissolved oxygen (DO) on horizontal transmission. Forty-five fish orally inoculated with E. seriolicida (2.9×109 CFU/fish) (donor fish) and an equal number of non-inoculated fish (recipient fish) were reared in separated net cages kept in a tank with high oxygen concentration (HDO, 112∼161% oxygen saturation) for 20 days. The same set of fish was kept in another tank with low oxygen concentration (LDO, 59∼82% oxygen saturation).
Average mortality of the donor fish in LDO group was higher than that of HDO group. Although there was no mortality among recipient fish in HDO tank, 5 recipient fish died in LDO tank. E. seriolicida was isolated from the recipient fish in LDO tank, but not from those in HDO tank. The venous blood oxygen tensions of the recipient fish in LDO tank were significantly lower than a control value measured prior to the experiment.
These results indicated that horizontal transmission occurs more easily among yellowtail kept in hypoxic than in hyperoxic conditions.
