A Primary Study On Molecular Genetic Differences And Growth Of Different Loach Populations In The Yangtze River Basin

Loach(Misgurnus anguillicaudatus)belongs to Cypriniformes,Cobutudae,Cobitinae,Misgurnus, it is one of the freshwater fish which is very popular in domestic and foreign markets in recent years, and it has become an important object of aquaculture because of its character of good adaptability,less disease,high survive rate and convenient transportation. But, the fry used in the loach cultivation mostly come form natural waters at the present time, the genetic backgrounds and the growth-performance of different loach populations are not the same, and it has become tremendous pressure to the producton management. In this sdudy, the SSR genetic marks and the growth-performance of different loach populations in the Yangtae River Basin were analyzed comprehensively, and the age and growth of Misgurnus anguillicaudatus and Paramisgurnus dabryanus was studied, providing essential throretical support for further study of germplasm resources protection and genetic breeding. The major results are as following:1. Microsatellite DNA Marker Analysis of Genetic Diversity of the Loach (Misgurnus anguillicaudatus) Populations in the Yangtze River BasinNine microsatellite loci were used for analyzing six wild loach populations(Suzhou population, SZ,Gaoyou population, GY,Anhui population, AH,Hunan population, HN,Hubei populations, HN,Jiangxi population, JX), Observed (HO) and expected (He) heterozygosity values, polymorphic information content (PIC) , and number of effective alleles (Ne) were all detected. Genetic similarity index and genetic distance were computed based on the allele frequency. The Hardy-Weinberg Equilibrium was checked according to the test ofχ2. Genetic differentiation and hierarchical partition of genetic diversity were evaluated by Fst and Nm. A clustering dendrogram was made based on the results of UPGMA methods using MEGA 3.1 software. There were totally 352 fragments ranging from 105bp to 383bp in length. 1 to 4 alleles were amplified at the nine loci and 27 alleles in all 6 loach populations. The average number of alleles in each locus was 3. The results showed that:(1)The level of genetic variability was relatively low in the six populations. Polymorphic information contents of the six wild loach populations were 0.2731,0.3928,0.3906,0.2901,0.3351 and 0.2319 respectively. The average numbers of effective alleles were 1.5881,1.9577,2.0336,1.6305,1.7652 and 1.5124. The average expected heterozygosity values were 0.3130,0.4614,0.4658,0.3641,0.4019 and 0.2866 respectively;(2)The genetic differentiation of 6 loach populations was obvious, the average value of coefficient of genetic differentiation for all loci was 0.2147, and the average valure of gene flow(Nm) was 0.9146.(3)The highest genetic similarity index that came form the populations of JX and HN was 0.9535, the lowest index was 0.5804, and it came form the populations of SZ and JX. There was a certain correlation between the clustering result and the geographical distribution.2. Comparison of Growth-Performance of different Loach (Misgurnus anguillicaudatus) Populations in the Yangtze River BasinThe comparative experiments of growth of loach offsprings of Suzhou population (SZ),Gaoyou population (GY),Anhui population (AH),Jiangxi population(JX),Hunan population(HN),Hubei population(sHN) and Suzhou population (♀)×Gaoyou population(♂)(GS)were proceeded during 124 days from August 2th to November 4th in 2008:(1)Absolute growth rate(g/d): GS﹥SZ﹥GY﹥AH﹥HN﹥HB﹥JX, GS was 16.7%,14.0% higher than GY and SZ respectively, there was most significant differences between GY and other six loach populations(P﹤0.01), the difference between GY and SZ is not signidicant, and the absolute growth rate of the two population are higher than that of AH,JX,HN and HB.(2)Variation coefficients of body weigh(t%): HN﹥HB﹥JX﹥AH﹥GY﹥GS﹥SZ, the variation coefficients of body weight of SZ was the lowest, and the varitation coefficients of JX,AH,HN and HB were higher than that of GY and GY.(3)Survival rates(%): SZ﹥GS﹥GY﹥AH﹥HN﹥JX﹥HB, thereinto, the average survival rate of SZ was the highest(96.7%), and that of HB was the lowest(86.0%), there were significant differences between any one of four loach populations and GS(P﹤0.05) except GY and SZ(P﹥0.05). In a word, based on the evaluation of growth performance and survival rate, the GY and SZ all shows excellent cultivation performances in the current environmental conditions of Suzhou. The growth performance of GS is superior to its parent populations, and shows better cultural potential.3. Primary stydy on the age and growth of the loach ( Misgurnus anguillicadudatus)and large scale loach (Paramisgurnus dabryanus)The scale was choosed as age identification materials of Misgurnus anguillicaudatus and Paramisgurnus dabryanus, and the two kinds of fish were determined by the conventional biology methods. The results showed that the relationships between the body length and the scale radius of Misgurnus anguillicaudatus and Paramsigurnus dabryanus is beeline correlative and the expressionses were L = 99.577R + 9.7435(r = 0.997)and L = 74.445R + 9.6442(r = 0.995). The growth trait of the length and weight of these two fishes was similar: W = 0.0118L2.8644(r = 0.899); W = 0.0146L2.8135(r = 0.923). The body groth pattern can be well described by Von Bertallanffy equation(P﹤0.01)and they were Misgurnus anguillicaudatus: Lt = 25.90[1-e-0.191(t+0.806)], Wt = 135.90[1-e-0.191(t+0.806)]3 and Paramsigurnus dabryanus: Lt = 25.59[1-e-0.201(t+0.731)], Wt = 169.45[1-e-0.201(t+0.731)]3。The stage before the age of 3 was a speediness growth phase of body length. The ages of growth turning point of body weight of the two fishes were 4.95 years and 4.73 years respectively.