Interspecific hybridization of sturgeon species affects differently their gonadal development

Gonad development in fish is generally assumed to be negatively influenced by interspecific hybridization, resulting in sterility or sub-sterility. However, this is not the case in sturgeons (Acipenseridae), in which fertile hybrids are common. In the present study, we investigated gonad development in several sturgeon interspecific hybrids and purebred species. Six interspecific hybrid groups and three purebred groups were analyzed including 20 hybrid specimens with even ploidy, 40 specimens having odd ploidy levels, and 30 purebred specimens. Hybrids of species with the same ploidy (even ploidy - 2n, 4n) exhibited normally developed gonads similar to those seen in purebred specimens. In contrast, hybrids of species differing in ploidy (odd ploidy - 3n) did not display fully developed gonads. Ovaries were composed of oocytes or nests of differentiating oocytes that ceased development in early stages of meiosis (pachytene to zygotene) with a higher content of adipose and apoptotic tissue. Testes contained single spermatogonia along with Sertoli cells and spaces lacking germ cells. The obtained results showed that gonad development was influenced by genetic origin and ploidy of the sturgeon hybrids and were consistent with full fertility of hybrids with even ploidy. Sterility of females, but possibly limited fertility of males, is suggested for hybrids with odd ploidy.