Study on artificial induction, growth and gamete quality of mitogynogenetic turbot Scophthalmus maximus

Abstract

Artificial gynogenesis induction is one of the important techniques of chromosome manipulation. The eggs are fertilized with inactivated sperm to prevent the inheritance from the paternal genome, and genome information of the offspring is totally contributed by the maternal genome. Mitogynogenesis, in which diploidization of chromosome set is performed by blocking the cleavage, is theoretically homozygous and has got more attention in breeding. In this study, we performed the mitogynogenetic diploid induction in turbot Scophthalmus maximus, one of the most important maricultural fish in China and Europe, by applying hydrostatic pressure to the eggs activated with UV-irradiated homologous sperm. The optimal inducing conditions were 36,000 erg mm-2 for UV-irradiated and pressure of 65 MPa for 6 min at 15 min before the appearance of the cleavage furrow. Two mitogynogenesis stocks were obtained in 2016 and 2017. The results showed that there was no distinct difference in incubation time and morphological traits between mitogynogenetic diploid and control diploid. The survival rates of mitogynogenetic diploid sharply decreased in the first month post hatching (mph). Their total weight (tW) and total length (tL) increased rapidly from 12 to 18 mph. The mitogynogenetic diploids induced in 2016 and 2017 showed very different growth. The mean tW and tL of 10 fast-growing individuals at 18 mph were 2.78 and 1.32 times of the others in 2016 stock, while 4.50 and 1.74 times in 2017 stock, respectively. The higher male ratio and rising trend of male ratio indicated the female heterogametic ZW/ZZ genetic mechanism of sex determination in turbot. Twenty-four adults in 2017 stock survived until 24 mph. While twenty-nine adults in 2016 stock survived until 36 mph, in which 11 adults could be promoted mature. Then the qualities of gametes were evaluated and showed that both the egg and the sperm qualities of mitogynogenetic diploid were lower than those of control diploid. However, the embryo and larvae development showed no difference between mitogynogenetic diploid progeny and control diploid.