Study On Biology And Heredity Of Paracobitis Variegates In Daning River

Paracobitis variegates are distributed in the trunk and its branches of the Yangtze River system within Sichuan Province,the upper Wei River and its branches, belonging to the Yellow River system,the Bailong River within Gansu Province （Ding Ruihua,1995） and the Jinsha River and the Nanpan River system within Yunnan Province.During the period from October,2006 to November,2007,313 samples were collected from the Wuxi Section of the Daning River.Researches on their age structure,growth characteristics,food compositions and genetic structure were made by applying routine biological methods.,with the aims of accumulating basic data on the growth,resources and environments of small-sized fishes,and of providing a scientific base for the protection and assessment of fishery resources in the district of the Yangtze Gorges Reservoir.The results are as follows:1.It is feasible and effective to use the otolith of P.variegates as the material for their age determination.The lapillus is similar to a horse’s hoof in shape,with its frontal end being bluntly circular,its back end inflate,its inner side fairly flat,and its outside bulging,.After polishing,it presents the shape of an irregular ellipsoid.Being quite deep,its central region is approximately a circular dark area under incident light, Outwardly are annual rings in which wide dark bands are alternatively arranged with narrow light ones.asteriscus is a slice that is concave in the middle.It is an ellipsoid in shape,with its inner side sinking and outside bulging.After polishing,its rings are clear and easily recognizable.2.The relationship between the otolirh diameter of P.variegates and their body Length is L=263.24R+9.03（R=0.986,n=129）;the relationship between their body weight and body length is W=1.95×10^-4L^2.309（R=0.9493,n=129,F=1186.254） L_t=222.708(1-e^{-0.092（t+2.162）}) W_t=51.399(1-e^{-0.092（t+2.162）})^2.309.The inflection age for growth of P.variegates in body weight is 6.97 years.3.P.variegates is a carnivorous fish species,the food compositions of which are mainly benthic insects,with Ephemeroptera,Coleoptera and Trichoptera having the highest occurrence.Occasionally,earthworm and small fish appear in the digestive tract of a few fish individuals.The ratio of male（♂） to female（♀） of P.variegates is 1.59.The minimum absolute fecundity（F）is 254 eggs, while the maximum absolute fecundity（F）is 652 ones,with the mean absolute fecundity being 383±268.The minimum relative fecundity（F_s） is 38 eggs,while the maximum relative fecundity（F_s） is 179 ones,with the mean value being 80±42.4.The sequence of mtDNA cytochrome b of P.variegates is 1140 bp long., with the contents of A,T,G and C in the gene fragment being 27.9%,28.3%,16.2% and 27.6%,respectively.,showing marked anti G bias..A total of 13 varied sites were found,accounting for about 1.14%of the total number of sites analyzed.Of the varied sites,7 are single polymorphic sites,and 6 contain brief informantion.18 sequences are clustered into 10 haploid types.The NJ phylogenetic tree,constructed on the genetic distance among their haploid types,consists of 2 branches..The mtDNA sequence of the population of P.variegates in the Daning River contains rich polymorphism,indicating that this population has rich genetic diversity.