Pike-persch or zander, Sander lucioperca (syn. Stizostedion lucioperca) is a freshwater fish sometimes found in brackish habitats. It is closely related to the perch. In Europe, a second species (Sander volgensis) is limited to rivers in southern Russia and the basin of the Danube. These two species are suspected to hybridize occasionally where they are sympatric, as they produce fertile hybrids in captivity; no natural hybrids are known yet however, and while they are apparently hard to detect, it is suspected that the species are separated by strong prezygotic isolation. Danube Delta, Romania.