Natural Hybrid Posterities - Problem for the Existence of the Acipenseridae Family Species in Nature

During the period 2005 - 2010 in Bulgarian territorial waters of the Black Sea and the Danube River four interspecies hybrids of sturgeons were caught. Hybrid No 1 was defined as Ship sturgeon (Acipenser nudiventris) x Russian sturgeon (Ac. gueldenstaedti) - second or third generation. Hybrid No 2 - Ac. stellatus x Ac. ruthenus. Hybrid No 3 - Huso huso x Ac. ruthenus (bester). Hybrid No 4 was with morphological signs of Russian sturgeon (Ac. gueldenstaedti) and Sterlet (Ac. ruthenus). The simultaneous catch of more than one specimen at the same time and place, supports the view that the amount of obtained natural hybrids in populations of sturgeon species with drastically reduced numbers increases.