Study On Molecular Systematics, Speciation And Biological Characteristics Of Zacco Platypus (Cypriniformes: Cyprinidae) In China

Zacco platypus (Cypriniformes: Cyprinidae) is one of the endemic freshwater fishes in the East Asia, widely distributed in China, Japan, Korean and Vietnam. In China, Z platypus is distributed in main eastern river systems. The fish always lives in small rivers around mountains and has some commercial value for local people.We studied on the molecular systematics of Zacco platypus, based on the complete sequence of cyt b gene of mitochondria of 106 samples (38 are our samples and 68 from Genbank) distributed in 6 main river systems including Amur, Yalu-Jiang, Hai-He, Huai-He, Yangtze and Pearl River basins. Two main Zacco lineages, North and South Clades, were isolated by the Qinling Mountains. The South Clade had two clear Sub-clades: Sub-clades Yangtze and Pearl isolated by the Nanling Mountains. Genetic distance between the North and South Clades was up to 14.9%, which shows high genetic variance interaspecies. There were 59 haplotypes out of 106 specimens, which indicates high haplotype diversity. Analysis of molecular variance (AMOVA) showed that genetic variance between clades was the highest and between drainages in one clade was the lowest.Based on the results of the molecular systematics, we used multivariate morphometrics and landmark methods to analyze 41 geographical populations distributed in 6 major river systems of China. According to the Principal Component Analysis (PCA) of 53 external characters including 10 meristic characters and 43 morphmetric characters, Zacco in mainland China had morphological differences between the North and South Clades. On the morphological variations, mouth width, caudal-peduncle length and the distance from inferior border of opercular to origin of pectoral fin of North Clade were bigger than South Clade. We also analyzed the morphological variation within each Clade and the results displayed the differences within the North Clade and no difference within the South Clade.Combining the results of the molecular systematics and the morphometrics, the North and South Clades should be recognized as two species because of high morphological and genetic variances. Both evolution history and distribution pattern of Zacco are related to the geographical events appeared in the Late Tertiary. According to the fossil records, the ancestors of the current Zacco might origin and mostly spread all over the East Asian at the Early Tertiary. Based on the molecular clock, we estimated that the divergent time of the North and South Clades is about 9.8-7.0 million years ago probably due to the lift of the Qinling Mountains. The divergent time between the Sub-clade Yangtze River and the Sub-clade Pearl River is about 4.3-3.6 million years, which may be related to the Qinghai-Xizang movement, especially the Qinghai-Xizang movement Act A (3.6 MaBP).In addition, the characteristics of the age, growth, food and reproduction of Zacco platypus in Beijing were also investigated. Maximum ages are observed as 3 years for males and 2 years for females. The equation of body length-weight relationship is BW (Body Weight) =1×10⁵L^3.1279 (r=0.9477), NW (Net Weight) =8×10^-6L^3.1404 (r=0.9478), which explains their growth is allometric. The Von Bertalanffy equation of male is L_t=121.56×(1-e^{-0.3718(t+0.6272)}, maximum body length is 121.56mm, W-t=18.26×(1-e^{-0.3718(t+0.6272)3},maximum body weight is 18.26g, growing inflexion is 2.41 years. The Von Bertalanffy equation of females was not established because their maximum ages are 2 years old. The fullness and the fillness index showed annual changes, which may be attributed to the changes of the water temperature and idiophase. The investigation on food contents displayed that the food in the fish gut mainly consisted of alga and the fish might select their favorite speices. The sex ratio of the fish was close to 1:1, and the mature age is 1 year. The main spawning season is estimated to be from April to July and the peak of reproduction is in May. Based on the biological characteristics and living environment, we suggest to control fishing amount, choose fitable fishing season and protect living condition so as to maintain sustainable use of local Z. platypus.