| Genetic breeding has been one of the most important way to improve productivity of agriculture plants and animals. In aquaculture species, especially in which only wild population is cultured, genetic improvement will play more important role in raising productivity. Here we report genetic breeding practice in olive flounder Paralichthys olivaceus using two major breeding methods: selection and chromosome manipulation for sex control. We also report the QTL analysis for growth speed with AFLP markers.1. Meiotic gynogenesis in P. olivaceus was induced by cold shocks to the eggs fertilized with UV irradiated sperms. Using 2 paralleled UV light (20W each), the optimal time of UV irradiation for effective inactivation of P. olivaceus sperms was 60sec when the distance between sperms and the UV light was 10cm. Results of developmental potential showed that when the fertilized eggs were maintained at 15 ?0.5℃ before any treatment, chromosome diploidy was achieved by suppression of the second polar body release by early cold shocks applied l-10min after fertilization at 0-10癈 with 15-90min durations. For obtaining maximal rate of diploidy(79. 7%) in this species, the optimal cold shock was at 2-4癈 that was applied at 3min after fertilization and lasted 45min. The haploid chromosome number of untreated embryos and the diploid chromosome number of putative diploid gynogens indicated the effectiveness of UV irradiation and cold shocks, respectively.2. Meiotic gynogenesis in P. olivaceus was also induced by hydrostatic pressure shocks. Chromosome diploidy was achieved by early pressure shocks applied 1-lOmin after fertilization with pressures range in 40-65MPa that lasted for 2-10min. The optimum pressure condition to induce maximal diploidy (61%) of meiotic gynogenesis was 55MPa pressure that was applied at 3min after fertilization and lasted for Grain.3. Mitotic gynogenesis was induced by hydrostatic pressure shocks forthe first time. Chromosome diploidy could be achieved by suppression of the first cleavage by late pressure shocks applied 40-100min after fertilization with pressures range in 45~70MPa that lasted for 2-10min. The optimum pressure condition to induce maximal diploidy (18%) of meiotic gynogenesis was 55MPa pressure that was applied at 3min after fertilization and lasted for 6min.4. AFLP technology was used to mark the growth differences in cultured population and QTL analysis for growth speed. Large and small individuals were divided into two groups and compared. Among 96 pairs of primers, 6 pairs were selected for growth analysis. A total of 444 loci were amplified, of which 49.*78% were polymorphic. One factor variance analysis indicated that 48 loci were associated with body length, of which 35 loci were positively related at 0.01 level. The same analysis also selected 52 loci that were related to body weight, in which 38 loci were found to be highly positively related. One locus was found only in small group.5. Mass selection was applied to select fast growth trait for two successive generations. The selection intensities were 3% and 8% in the first and second generations, respectively. The growth performances of the offspring of selected population were compared in cage and indoor cultures with that of wild population of the same age. The growth rate of the second generation was 9.02% higher in cage culture and 6.92% in indoor culture than that of wild population, and the growth of the third generation was 36. 3% higher in cage culture and!9. 2% in indoor culture than that of wild population, respectively.The present study proved the effectiveness of selection and the possible use of molecular markers in the selection for growth, and provided possibility of sex control in this species. |
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