Studies On Genetic Variation Of Different Populations And Disease Resistant Stock Selection Of Feneropenaeus Chinensis

Feneropaeneus chinensis which is mainly distributed in the Yellow Sea and Bohai Sea in China plays a very important role in both marine catching fisheries and marineculure. However,in 1990's the production of shrimp catch and mariculture dropped dramatically. The shrimp dropped from thousand tons to hundred tons though large scales enhancement has been carried out annually by releasing of hatchery raised fries. In 1993 an epidemic outburst of viral disease in 2.2 million mu of pond-cultured shrimp brought about a great decline in production in spite of much ameliorative measure taken to improve culture mode and culture technology. The genetic diversity of natural populations and culture stocks were investigated and genetic selection for disease resistant ability were carried out in a cultured stock in order to provide information for natural resources management and exploitation.Four populations of F. chinensis,including 2 natural populations(YP and KP)and 2 cultured stocks(CS1 and CS201)were investigated. YP is collected from the spawning ground in Jiaozhou bay in the Yellow Sea(36 37'N,121 OOE),KP is collected from the spawning ground along the Korean peninsular(35 34'N,126 00 E). CS1 is the fourth generation of Bohai Sea wild population surviving the WSSV(White spot syndrome virus)epidemics in the grow-out ponds. YP,KP and CS1 were analyzed by RAPD(Random amplified polymorphism of DNA),while YP,KP,CS1 and CS201 were analyzed by isozyme.The robust and biggest individuals were selected from CS201 in selection breeding. CS202and CS203 were the second and third generation surviving the epidemic. Disease resistant ability was assessed by oral infection. The genetic variation of the three successive generations were analyzed by AFLP(Amplified fragment length polymorphism).Both the RAPD and isozyme results showed that the genetic diversity of F.chinensis was relatively low and the genetic marker showed relatively high conformity within or among populations. RAPD results showed that the genetic diversity of KP was the highest and YP was intermediate while the CS1 was the-lowest. Among the 4 populations analyzed by isozyme,the percentage of the polymorphic loci and the heterogeneity of 8201 was the highest of the 4 populations;Judged by differentiation index,genetic differentiation was found between populations. -The selected C.S203 died.more slowly than unseleeted control and the survival rate of the former was increased by 60% in the same period in the oral infection.test. The viral pathogen was discovered in more than 60% individuals in both the selected and unseleeted stocks,which implied the selection increases the disease resistant ability for WSSV. There was no obvious change in genetic diversity between the CS201 and CS202,but the genetic diversity of 8203 is lower than the former 2 stocks.It can be concluded from the experiment results that hatchery seed has lower genetic variation and large-scale hatchery seed releasing affects the genetic diversity of the natural population. The shrimp distributed along China coast in Bohai Sea and Yellow Sea may consist of more than one populations. The viral disease resistant ability of F. chinensis is proved to be genetically inherited and can be improved by genetic selection.