"Oxygene" was a designation for oxygen-breathing species, as opposed to those who breathed other gases.
In 2370, while discussing interspecies relationships with Ensign Melora Pazlar, Lieutenant Jadzia Dax used the story of a hydrogen-breathing Lothra and an Oxygene who had fallen in love and were only able to spend forty minutes a day together without their breathing apparatus. This was to illustrate how Pazlar and Doctor Bashir could find a way to make a relationship work, despite her hailing from a planet with lower gravity than Bashir's homeworld, Earth. According to Dax, the couple were together 57 years despite their difficulties. (DS9: "Melora")