In a previous study (33), we showed that the barophilic strains isolated from the intestinal contents of deep-sea fish contained DHA and EPA. Furthermore, we found that bacteria containing DHA were generally and abundantly distributed in the intestines of deep-sea fish, compared with shallow-sea poikilothermic animals (34), suggesting the involvement of DHA in the adaptation to deep-sea environments. Thus, in the present study, we initially examined the lipid compositions of a barophilic strain which contained DHA in its lipids. Next, we examined the effect of growth pressure on the phospholipid and the fatty acid compositions in facultatively and obligately barophilic strains containing DHA.