Sturgeon is the common name for the 27 species of fish belonging to the family Acipenseridae. Their evolution dates back to the Triassic period some 245 to 208 million years ago. The family is grouped into four genera: Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus. Sturgeons are native to subtropical, temperate and sub-Arctic rivers, lakes and coastlines of Eurasia and North America. Several species of sturgeon are harvested for their roe, which is processed into the luxury food caviar. This has led to serious overexploitation, which combined with other conservation threats, has brought most of the species to critically endangered status, at the edge of extinction.