On the theory that bubbles originate from preexisting micronuclei, we previously demonstrated that pretreatment with hyperbaric O2 (HBO2) reduced the number of bubbles in the prawn decompressed from 203 kPa. In the present study, we examined the effect of two HBO2 pretreatment pressures (405 and 709 kPa) on prawns decompressed from a range of pressures between 203-810 kPa. Prawns from the experimental groups were pretreated with O2 at 405 or 709 kPa for 5 min (series A and series B, respectively). Prawns from the control groups were exposed only to air. Following pretreatment, prawns were exposed to air at the desired pressure until saturated with nitrogen, then subjected to rapid decompression and examined under a light microscope. Series A: HBO2 pretreatment at 405 kPa for 5 min significantly reduced the number of bubbles after decompression from 203, 304 and 405 kPa (p < 0.05). The total volume of accumulated gas was not affected by HBO2. Series B: Pretreatment with HBO2 at 709 kPa significantly reduced the number of bubbles after decompression from 203, 304, 507 and 608 kPa (p < 0.05). Total gas volume after decompression from 507 and 608 kPa was reduced as a result of pretreatment with O2. This study demonstrates that HBO2 pretreatment at 405 kPa is sufficient to reduce the number of bubbles that will emerge on decompression from several levels of compression.