"Oxygene" was a designation for oxygen-breathing species, as opposed to species needing other gases to breath such as hydrogen.
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 to illustrate how Pazlar and Doctor Bashir could find a way to make a relationship work. According to Dax, the couple were together 57 years despite the difficulties. (DS9: "Melora")