Gender-Bending Fish Swap Sexes in Harems Wild hawkfish change gender to suit the moment By Neal Colgrass, Newser Staff Posted Jan 7, 2012 3:05 PM CST 18 comments Comments The dazzling, transgender Hawkfish. (Wikipedia) (Newser) – Talk about a dynamic dating scene. The richly colored hawkfish of southern Japan can transform into a female or male depending on circumstances to improve their reproductive chances, New Scientist reports. Many marine animals change gender during a lifetime, but in the hawkfish, scientists have for the first time discovered fish who become male or female to suit the moment. At issue is the dynamic in hawkfish harems. If the male leader has too many females, a larger gal will swap sex and take over half the group. If that fish loses females to other harems and faces competition from another, larger male, it can switch back to female. Hawkfish "will show behavioral changes within minutes and structural changes in the tissues within days," one ecologist says. "These animals are a lot more flexible than some species."