Reproductive Characteristics of Reciprocal Hybrids of Sturgeon Species with Different Ploidy Levels: Sterlet Acipenser ruthenus and Kaluga A. dauricus (Acipenseridae)

We present the reproductive characteristics of fertile reciprocal hybrids of two sturgeon species with different ploidy levels, sterlet Acipenser ruthenus and kaluga A. dauricus, obtained for the first time. The ability of these hybrid males and females to produce viable offspring in backcrosses is discussed in the light of previously obtained data on the origin of the sterlet × kaluga hybrid female as a result of fertilization of the unreduced sterlet egg by kaluga sperm and the production of sperm with different numbers of chromosomes by hybrid sterlet × kaluga males and unreduced eggs by hybrid kaluga × sterlet females. Based on a number of studied biological characteristics (body size, time of first maturation, spawning cycle, and egg size), a manifestation of the maternal effect is noted in hybrid specimens. The differences in the egg size are also explained by the fact that the eggs of kaluga× sterlet hybrid females are triploid in relation to the haploid number of chromosomes (60), and the eggs of female sterlet × kaluga are diploid.