| More than 1500 kinds of fishes exist in the Chinese coastal areas, and most likely have an economic value. Cutlassfish (Trichiurus haumela) is an important member of the four major commercial marine fishes of China (yellow croaker, Chinese herring, cutlassfish and chub mackerel), because of its wide distribution, large size and high production. The cutlassfish distributes in warm waters around the world widely. They are found in all Chinese waters including East China Sea, Yellow Sea, Bohai Sea, South China Sea and the northern Bay. However, due to overfishing, pollution and deterioration of marine ecosystem, the production of cutlassfish decreases. Besides, the genetic diversity of cutlassfish declines sharply. Flounder (Paralichthys olivaceus) is the dominant fish species in the marine fish farming of North China. With the rapid development of artificial breeding industry of flounder, the demand of seed increases year by year. In recent years, the lower level of genetic structure was resulted by long-term artificial selection and breeding in flounder. Molecular marker technology provides a powerful tool for understanding the genetic differences between individuals from the DNA level directly. Microsatellite DNA marker becomes a popular molecular marker in analysis of population genetics, because of its high level of polymorphism, high information, co-dominant Mendelian inheritance, simple operation and stable result. Three items were studied in this paper, including:(1) Isolation of polymorphic microsatellite markers of cutlassfish; (2) Correlation analysis between genetic distance among parents and growth rate of offspring in Paralichthys olivaceus; (3) Family identification and parentage determination in farmed Japanese flounder using SSR. The main research results are as follows:1. Isolation of polymorphic microsatellite markers of cutlassfish:A (GT)n enriched genomic library was constructed for cutlassfish using the FIASCO method (fast isolation by AFLP of sequences containing repeats). After sequencing,68. clones were found containing microsatellite repeat sequences. Finally, PCR primers were designed for 36 loci successfully, of which 12 loci showed polymorphic. This could be useful for the further study of the genetic structure, genetic diversity of cutlassfish.2. Correlation analysis between genetic distance among parents and growth rate of offspring in Paralichthys olivaceus:Using microsatellite technology,21 polymorphic microsatellite markers were used to study the genetic diversity of Japanese flounder parents. The genetic distance of 32 parents was computed. Simultaneously, the correlation between parent SSR genetic distance and the growth rate of their offspring was assayed using SPSS software. The results showed that the mean observed heterozygosity (Ho), expected heterozygosity (He), and polymorphism information content (PIC) of these 32 parents was 0.6931,0.6784,0.6237, respectively. It illustrates that this parents population possesses high genetic diversity level, strong ability to adapt to environmental change, and high breeding capacity. Meanwhile, it showed that the genetic distance of parents ranged from 0.2578 to 0.9773. As the parental genetic distance for 0.2578～0.5958, the correlation between growth rate of offspring and parental genetic distance appeared to be positively significant at P<0.05; As the parental genetic distance for 0.6099-0.6604, there was no significant correlation; As the parental genetic distance for 0.6640～0.9773, the correlation between growth rate of offspring and parental genetic distance appeared to be negatively significant at P<0.05. This is of great significance for cultivating rapid growth breed, so as to improve the quality and economic benefit of artificial farmed flounder.3. Family identification and parentage determination in farmed Japanese flounder using SSR:Eight hyper-variable microsatellite loci were selected to execute the family identification and parentage determination in aquaculture populations for Japanese flounder (Paralichthys olivaceus).180 offsprings from nine families (established in 2007) and 32 broodstocks were used in this study. At the same time, the influence of the number of microsatellite markers to the family identification accuracy was investigated. It was found that the number of alleles per locus in the offspring was reduced 13.9% compared to the broodstock. The average heterozygosity of offsprings (He=0.7702) was lower than that of their parents (He=0.8044). Fourteen family unique alleles were found out:one in 39#, 61# and 69# family, respectively, two in 36# and 68# family, respectively, three in 47# family, and four in 82# family.148 out of 180 juveniles were successfully assigned to their real parents after parentage analysis. The study result also demonstrated that 4 loci were required to assign 94% of progeny and 5 loci to assign 97% of progeny. It shows that microsatellite DNA markers could be used as a powerful tool for determining kinship, gaining pedigree information in selective breeding programs of flounder. |
PDF Full Text Request