Ploidy level and performance in meiotic gynogenetic offsprings of grass carp using UV-irradiated blunt snout bream sperm

Diploid (2n) gynogens, triploid (3n) hybrids and 2n hybrids fish were produced in meiotic gynogenetic offsprings of grass carp (Ctenopharyngodon idella) eggs using UV-irradiated blunt snout bream (Megalobrama amblycephala) sperm. Flow cytometry revealed that a total of 306 (54.2%) 2n gynogens, 157 (27.7%) 2n hybrids and 102 (18.1%) 3n hybrids were identified at one year old stage examined. Chromosome analysis showed that 2n gynogens and 2n hybrid individuals had the same chromosome number as their parents (2n = 48), while the chromosome number of 3n hybrids was 3n = 72. The morphological characters of 2n hybrids and 3n hybrids were intermediate between their parents, and the 2n gynogens were similar to grass carp. Microsatellite genetic analysis showed that the expected heterozygosity (He) of 2n gynogens, 2n hybrids, 3n hybrids and grass carp control were 0.3775, 0.6518, 0.6601, 0.6502, respectively, and the polymorphism information content (PIC) was 0.3791, 0.5749, 0.5907, 0.5738, respectively. Compared with 2n and 3n hybrids, the He and PIC of 2n gynogens were significantly decreased, indicating that high homozygous could be obtained by the gynogenetic method. The 3n hybrids grew faster than both 2n gynogens and 2n hybrid individuals, suggesting that 3n hybrids had an obvious growth advantage.