The results of last year revealed that the genetic variability of grass shrimps capturedfrom the Tungkang coast is very high. The high genetic variability found in the wildpopulation of P. monodon may be related to the escape and release of the offsprings offoreign broodstocks which were imported continuously from many countries for thelarval production in the last thirty years. The objectives of this study is to analyze thegenetic variability and structure of Penaeus monodon from selected harbors aroundTaiwan. Wild P. monodon will be collected and the variability and structure ofmitochondrial DNA among population will be analyzed. The results of eachpopulations will be compared and the question of genetic contamination with foreignpopulations will be tested and revealed.