Study on artificial induction and early development of gynogenetic fat greenling Hexagrammos otakii

Fat greenling Hexagrammos otakii, belonging to Scorpaeniformes, is an important commercial marine fish species distributed in coast waters of China, Japan, and Korea. Artificial gynogenesis induction is one of the important techniques of chromosome manipulation and genetic breeding. The eggs are fertilized with genetic inactivated sperm, and genome information of the offspring is totally contributed by maternal genome. Until now, no gynogenesis induction was reported in H. otakii and other Scorpaeniformes species. The present study developed an effective gynogenesis induction method in H. otakii 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 20 min post fertilization. The relative hatching rates could reach 92%. The early development and growth before 6 month post hatching showed no difference between the gynogenetic and control diploid. The all-maternal inheritance was confirmed with 4 microsatellite loci. The genetic diversity of the control and gynogenetic diploid revealed with 20 microsatellite loci showed that the homozygosity of the gynogenetic diploid stocks was 0.84 in average, which was nearly double the value of the control diploid stocks (0.45 in average). Under scanning electron microscope, the egg envelop had a gelatinous-honeycomb before 0.5 h post fertilization (hpf). Then all or part of the gelatinous-honeycomb layer disappeared before 24 hpf. The uniform pores distributed to hexagonal pattern on the egg envelop were found in the control diploid and haploid groups. However, no pore on the egg envelop was found in the gynogenetic diploid from fertilization to hatching. These results would provide a valuable reference for gynogenesis induction in fish with viscous ovarian fluid coated eggs, although special incubation process to increase the survival rate should be further developed based on the characteristics of gynogenetic H. otakii.