Genetic diversity in crucian carp (Carassius auratus)

A survey of restriction fragment polymorphism in mitochondrial DNA of three subspecies of Carassius auratus throughout four provinces in China was und ertaken using 17 restriction enzymes. Two carp, Cyprinus carpio rubbrofuscu s and Cyprinus carpio carpio, were included as the outgroup. A total of 16 haplotypes was observed: 5 in tetraploids of C. auratus auratus; 8 in hexap loids of C. auratus auratus; and 2 in C. auratus gibelio and C. auratus cuv ieri, respectively. The tetraploids and hexaploids share three common haplo types as I, V, and VI. C. a. Cuvieri may have diverged first among the thre e subspecies. Interestingly, C. a. auratus and C. a. cuvieri did not form m onophyletic clades, which indicated that the classification of carassius au ratus required further studies. The current hypothesis, that hexaploids ori ginated from tetraploids by a polyploidy event, is less favorable, based on the distribution of haplotypes and the lower diversity in tetraploids than in hexaploids. Our data also indicate that divergence of hexaploids and te traploids might be recent and mtDNA polymorphism existed before the diverge nce. Meanwhile, genetic isolation exists between the hexaploids and the tet raploids.