Estimation Of Sustaining Yield In Poyang Lake Wetland And Analysis Of Genetic Diversity For Procambarus Clarkii Populations In The Middle And Lower Reaches Of The Yangze River Based On AFLP

The red swamp crayfish, Procambarus clarkii, native to south-central United States and Northeastern Mexico, has been transplanted to Hawaii, Japan, Europe and even the River Nile. They were introduced to Nanjing, China from Japan in1930s. This crayfish has rapidly spread to most provinces of China, and has established dense populations due to translocation by humans for food and lack of local predators. With increasing business demand and delicacy, the red swamp crayfish has been becoming an important fishery resource of Poyang Lake in recent years. At present, although the red swamp crayfish is widely distributed in the middle and lower reaches of the Yangze River basin, but little is known about the population genetics and invasion routes in China. However, habitat loss, overfishing and the crayfish plague have diminished red swamp crayfish population thoughout their area of distribution.In consequence, this study systemically analyzes the population structure and dynamics of the red swamp crayfish in the Poyang Lake wetland using the Bhattacharya’s and Von Bertallanfy’s analytical methods. The main purpose was to collect biological data necessary for the management of this species. Additionally, we estimated the genetic diversity of six crayfish populations in four Lakes (Hongze Lake, Poyang Lake, Dongting Lake and Yue Lake) using amplified fragment length polymorphism (AFLP).The main results of this study are as follows:1. The body length of the sample group ranged from20mm to105mm; the dominant length group was70-85mm, which was approximate60.0%of the total; the dominating fishing time ranged from May to August; the best body length for fishing is above80.0mm.2. The present study showed that the population structure consisted of a maximum of5.58age classes for females and3.25for males, which indicated that the crayfish is a relatively short-lived species.3. The Y’/R analysis showed that Epresent>E0.5, which exceeded the optimization (Eopt) criterion of0.5for sustainable exploitation of fisheries, so this specie was over exploited in Poyang Lake. 4. The Lc(mean length at first capture) equals to67.5mm. The estimated mesh size for catching the red swamp crayfish equals to13.5mm.5. The virtual population analysis model (VPA) showed that the largest annual catch of red swamp crayfish is3.43×104t. Maximum Sustainable Yield (MSY) is1.18×104t.6. The low natural mortality rate range of0.68～1.11year-1suggested that it is ecologically worthwhile to allow the red swamp crayfish to grow to larger size to contribute to the biomass for biologically optimum exploitation. This could be facilitated by adoption of closure measures to conserve the fishery.7. A total of89loci were generated with five EcoRI+3/MseI+3primer combinations and scored as binary data in139individuals. These data were analyzed by cluster methods in the software package NTSYSpc. Five EcoRI-MseI primer combinations were used to evaluate genetic variation in6geographic populations of red swamp crayfish. PPB=75.74%, Ne=1.4181, Nei’s (1973) gene diversity H=0.5829, Shannon’s Information index Hpop=0.441. Therefore, among the six populations, the highest gene diversity was found within the Nanjing (HZ) population.8. Similarly, the estimated fixation index (Fst) value averaged across all polymorphic loci across the four lakes was0.4186, suggesting a high genetic differentiation. The analysis of molecular variance (AMOVA) demonstrated that most variation occurred within populations (91.20%).9. The six populations are separated into three major clusters by principal coordinate analysis (PCA) and cluster analysis (UPGMA). Interestingly, the water level is a crucial factor to affect the population structure of freshwater crayfish. These results will provide reliable information for future broodstock selection and management, and will help in the selection of high quality individuals for artificial reproduction.10. These results proved that the genetic differentiation of crayfish in the middle and lower reaches of the Yangze River was at a high level. Such information will provide reliable information for future broodstock selection and management, and will help in the selection of high quality individuals for artificial reproduction.