Analysis Of Genetic Diversity And Growth Phenotype Of The Selected Breeds Of Red Swamp Crayfish (Procambarus Clarkii)

Red swamp crayfish(Procambarus clarkii)is a highly economic aquatic animal.Breeds are the foundation of the aquaculture industry.At present,many factors make it difficult to cultivate the improved breeds of red swamp crayfish.There is a shortage of high-quality breeds in the market,which has limited improvement of the production.In this study,six wild red swamp crayfish populations were taken as the base population,and the population selection method was used to select the breeds with excellent growth characteristics at the same growth period to form the breeding population,which was cultured in the same way.The final growth phenotype and genetic diversity of unbred and bred populations were compared.The bred population of with excellent growth performance and abundant genetic variation were cultivated through cumulative selection of several generations.In addition,each population was always cultured in its own closed breeding ponds,and the terminal growth phenotype and genetic diversity of the basal population,bred population and their offspring were measured to investigate the effect of inbreeding within the population.The phenotype of growth traits in the unbred and bred crayfish juveniles were compared in each generation,the results showed that the average size of the bred juvenile crayfish was larger and the phenotypic variation between individuals were smaller comparing to those of the unbred juvenile.The body weight,body length,carapace length,carapace width and abdomen length were significantly correlated with each other.The final phenotype of the unbred population and the bred population was compared,and body length,carapace length and width were used as evaluation indexes.The results showed that the phenotype of terminal growth traits in the bred population was significantly larger than that of the unbred population,and the final phenotype of the bred population was continued to increase with the increase of the selection algebra,which had a cumulative effect.In each generation,body length,carapace length and carapace width were increased by 2.76%-12.63%,3.78%-12.36%,and 0.00-13.52%,respectively.All the basic population and bred population had moderate genetic diversity that was not changed significantly due to breeding process.At the same time,the terminal size of the offspring of the bred population was larger than that of the unbred population.However,with the increase of breeding algebra,the difference of terminal size between the offspring of the unbred population and the bred population was decreased,and the final phenotype of body size of the crayfish in the investigated offspring was also decreased,and the offspring had moderate genetic diversity.Due to inbreeding of each population in the closed environment,population terminal phenotype value of both the basic population and the bred population showed obvious decline,and terminal phenotype value of the growth trait in the population was decreased significantly with the increase of inbreeding algebra.In each generation,body length,carapace length and carapace width were reduced by 5.06%-10.00%,5.76%-11.00%,and5.56%-11.88%,respectively.However,the moderate genetic diversity of each population was not changed significantly with the increase of inbreeding algebra.The results of this study showed that the body size of red swamp crayfish was significantly improved in the bred population,but the genetic diversity of the bred populaiton was not decreased.However,inbreeding in red swamp crayfish population caused rapid decline in body size.Anyway,it is conclusion that the improved breed of red swamp crayfish may boost the development of crayfish industry.