Applications Of Genetic Markers In Fish Breeding And Ecology

Silver carp (Hypophthalmichthys molirix) and bighead carp (Aristichthys nobilis) are extensively distributed in the Yangtze River, Zhujiang River, Heilongjiang River and other lakes and they own the largest cultivation production in China. At present the germplasm qualities of the two species degenerate rapidly owing to lack of scientific management in artificial breeding and human activities, such as dam construction, overfishing. Therefore, to breed new varieties with a high yield, fast growth and disease resistance is an urgent task. Pure line construction is one of breeding methods and it achieves traditionally by carrying out sib mating of over 10 consecutive generations or two consecutive gynogenesis as well as sex reversal. But it is too long for silver carp and bighead carp because of their long life cycles. So the method was developed by adding RAPD marker selection to artificial gynogenesis and sex reversal. And we aimed to construct pure lines only through one gynogenesis. The river-lake connecting relationship among the Yangtze River, Poyang Lake and Ganjiang River is very especial and there are lots of spawning grounds in the Yangtze River and Ganjiang River. So we investigated genetic construct of the silver carp from the Yangtze River, Ganjiang River and Poyang Lake for understanding which population contributing most to Poyang Lake population. The value of PhiST was 0.0346 between Poyang Lake population and Ganjiang River population and this indicated that there was no apparent differentiation between them. So the two populations could be considered as one population. It was 0.1663 and 0.2020 between the Yangtze River population and Poyang Lake population and between the Yangtze River and Ganjiang River respectively, which showed their significant differentiation. So we made a conclusion that the composition of Poyang Lake silver carp population consisted mainly of Ganjiang River population. It was coincident with the fact that the water level of Poyang Lake outlet had always been higher than that of the Yangtze River during the spawning season of the silver carp. Yellow catfish, darkbarbel catfish and longsnout catfish are economic fishes distributing along the Yangtze River. But these fishes were separated by the natural barrier, the Three Gorges. The genetic diversities and genetic structure of these fishes were studied by the methods of PCR-RFLP and direct sequence of mitochondrial DNA fragments (ND5/6, Cytb and D-loop). The results indicated that apparent differenciation existed between the populations from upstream and mid-down stream of the Yangtze River. But there was no apparent differenciation among the populations from mid-down stream and it was concerned with the absence of barriers to prevent gene flow. Yellow catfish and darkbarbel catfish were very uniform in morphology and reproduction mode. However, with regard to genetic variances of Yellow catfish and darkbarbel catfish, the compositions of genetic variance were different. And it may result from the different life history of the two fishes. As for long snout catfish, the genetic diversities are very low. What's more, the abundance of long snout catfish is very low at present. So appropriate measures should be taken to conserve long snout catfish.