Scientists have discovered a molecular marker for sex determination in sturgeon within the international project STURGEoNOMICS, led by the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB). This discovery represents a significant breakthrough for evolutionary biology, for species conservation and for caviar-producing aquaculture. This genetic evidence characterizes the oldest known genetic sex-determining system in vertebrates with microscopically indistinguishable sex chromosomes. The short sex-specific DNA sequence, detected in several sturgeon species, can be traced back to a common sturgeon ancestor, 180 million years ago.