| Large yellow croaker is one of the most important marine farming fish in China, but the economic character of cultured large yellow croaker was severely degenerated, the genetic breeding work was pressingly needed. The Fish Genetics and Breeding Research Group in Jimei university was committed to the studies on genetic improvement of large yellow croaker from 2001, with 4 generation of consecutive breeding,"Minyou No. 1"was proved an exceptional strain. Our studies go in for the genetic structure and genetic diversity analysis of"Minyou No. 1"with microsatellite markers. Genetic parameter of this strain was estimated with the assistance of microsatellite pedigree tracing. The main results were as follow:1) Thirteen microsatellite markers were used to analyze the genetic structure and genetic diversity of the breeding populations"Minyou No. 1"from F1 to F4. The results showed that the genetic diversity of the breeding population was decreasing, the average polymorphism information content (PIC) of the 13 microsatellite markers decreased from 0.638 to 0.524, the average allele number from 5.462 to 4.308, the average heterozygosity from 0.779 to 0.532, the average Shannon's gene diversity index from 1.356 to 1.092, respectively. The genetic identity between F1 and its descendant generations (F2, F3, F4) decreased (from 0.7194 to 0.5813) while the genetic distance increased. The genetic identity between the adjacent generations increased and the Fst values decreased (0.0619 in F1-F2; 0.0511 in F2-F3; 0.0475 in F3-F4). The allele frequency of the loci LYC0002 and LYC0054 changed regularly in the four breeding generations and they might correlate with the selected traits, which should be approved by further research. Our study suggested that the selective breeding work were efficient, some adverse gene were phased out, the hereditary basis of the population was getting pure and the genetic structure would be stable with the continuation of the breeding work.2) Parental contributions were evaluated in 3 artificially bred batches of"Minyou No. 1"strain of P.crocea using parentage assignment with microsatellite markers. Among all the 959 investigated fish, a total of 955 individuals were assigned as progenies of 42 mating combinations at 95% confidence level (385/389, 323/323 and 247/247 for each batch, respectively). The results showed significant inequality of the progeny distribution among mating combinations. For some mating combinations, even no progenies were found; For some other mating combinations, the numbers of progeny were preponderant in the analyzed batch. The contributions of male parent were 1.2% to 47.1%, 1.0% to 89.3% and 2.0% to 61.9% for the batch 1, batch 2 and batch 3, respectively; whereas that of the female parent were 25.1% to 37.8%, 1.5% to 69.6% and 8.5% to 81.3% for the batch 1, batch 2 and batch 3, respectively.3) Genetic parameters was estimated by the MTDFREML program using the pedigree information which was given in parentage analysis. The results show that the heritability of total length, body length, body height, body weight of 13 month large yellow croaker was 0.06±0.051, 0.05±0.047, 0.10±0.068, 0.09±0.068, respectively. The low heritability results indicated that family selection method should be taken for better selective breeding result. The genetic correlation of the four phenotypic character of large yellow croaker was very large and all close to one. It means that other three phenotypic characters would obtain genetic improvement indirectly if one of the four was taken select breeding trait directly.
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