Research progress of the genetic diversity, origin and evolution of Carassius auratus in China

Carassius auratus is the important aquaculture fish in China and has high economic value, which can be classified into two subspecies: C. auratus auratus and C. auratus gibelio. C. auratus has strong adaptability, primarily inhabits freshwater and is widely distributed with complex genetic background and different morphology and ploidy. At present, scholars have studied the genetic diversity, origin and evolution of different C. auratus with various methods. And there are big differences in research results, due to the differences of research methods, objects and standards. This paper summarizes the resourses and genetic diversity as well as the origin and evolution of C. auratus in China. We found that there exist abundant germplasm resources and genetic diversity of wild C. auratus in China, and the genetic variation of different local groups of wild C. auratus is great, which indicated a great breeding potential of them. The same gynogenetic clones show high genetic homogeneity, and various gynogenetic clones display abundant genetic diversity. The genetic diversity of goldfish bred according to human preference is much lower than that of wild C. auratus. The origin and evolution of C. auratus gibelio, C. auratus var. pengze, and other C. auratus and goldfish are also discussed in this paper. Although the origin of C. auratus gibelio is controversial, most of the results still support the perspective that “C. auratus gibelio and C. auratus belong to the same species, and triploid C. auratus gibelio is a population differentiated from C. auratus under special circumstances”. C. auratus var. pengze may be exotic fish of natural waters which escaped from the pond where the C. auratus gibelio is raised or originated from the wild C. auratus, which has obvious growth advantages and was selected for its obvious fine traits. Also, the discovery of different gynogenetic clones makes the genetic relationship between C. auratus var. pengze, C. auratus gibelio, and wild C. auratus more complicated, and further comparative study is needed. In most areas of China, there are a high likelihood of independent origins of the triploid wild C. auratus gibelio, and a lower possibility of spreading to other water systems after forming in one place. That doesn't rule it out that the early history of fish farming induced the invasion of some C. auratus geographic groups. Goldfish may originate from the wild C. auratus in the middle and lower reaches of the Yangtze river in China. It first evolved into grass goldfish, and then differentiated into fantail goldfish and dragon-eye goldfish. Yet as time passed and with artificial selection, fantail goldfish was further differentiated into bubble eye goldfish and dragon-eye goldfish was further differentiated into oval goldfish. Although there are many varieties of goldfish, but they belong to the same maternal origin from the perspective of mitochondrial genome. By reviewing the previous research aiming at C. auratus in China, this study analyzes and discusses the present situation of germplasm resources, existing problems and future research of C. auratus, and provides a basis for reasonable utilization and protection of C. auratus resources, and to promote the good and fast development of C. auratus industry.