Artificial selection in the new breed of Fenneropenaeus chinensis named

After six- generation selection successively , Fenneropenaeus chinensis showed better economical traits such as fast growth and disease- resistance and so on. The average body length and the weight of each selective population increased by 8. 4% and 26. 86%, respectively, compared to the control. The morbidity was less than 10%, while it was more than 40% in the control. Genetic structure of each generation was also analyzed in the paper, the results were as follows: ( 1) Isozyme analysis: thirteen loci were examined and five loci were polymorphic, i. e. , MDH-2, GPI , MPI , PGM- 2 and PGM- 3. There were significant differences at the locus PGM- 3, and the gene frequency showed a decreased trend. At MPI locus allele C was found at the cultured populations, and the frequency showed an increased trend. ( 2) RAPD analysis: RAPD technique was used to investigate the genetic structure of five generation successively. The proportions of polymorphic loci showed a decreased trend while there was no difference between fifth generation and sixth generation. The degree of genetic differentiation ( Gst ) was moderate between populations except third population and fourth population. ( 3) SSR analy sis: eight loci were analyzed among five generations, and 108 alleles were detected. The average heterozy gosities showed a decreased trend while sixth generation remained the level of fifth generation. The values of Gst were less than 0. 05, which showed that there was differentiation to some degree but it was weaker.