Preliminary Evaluation And Analysis Of The Results Of Two Generations Breeding Of Grass Carp In Yangtze River

Grass carp(Ctenopharyngodon idellus)is an important freshwater fish in China.In this study,growth traits of F1 and F2 populations were compared by using the combination of barrel culture and mixed culture in the same pond.The genetic variance of breeding populations was analyzed by using mitochondrial DNA D-loop region and multiplex microsatellite PCR methods.For further comparison between the growth traits and disease resistance traits of different populations in the future.The SNP loci related to growth traits in GH gene were preliminarily developed.The pathological changes of liver in grass carp infected with Aeromonas hydrophila were preliminary analyzed in this study.The above results provide a powerful reference for developing a more reasonable and effective breeding programs in the future.The study includes following five contents mainly:1.In this study,the growth traits of F1 and F2 populations were compared by using the combination of barrel culture and mixed culture in the same pond.The results showed that the body weight of F2 populations was significantly higher than that of F1 populations during the whole 450 days except 30 days of age.The slope of linear regression equation of F2 generations was higher than F1 generations.It means that the daily gain of F2 populations was larger than that of F1 populations.The results showed that SGR,RGR and AGR of F2 populations were 0.91%,4.92% and 14.77% higher than those of F1 populations at 150 days of age.The above three parameters of F2 populations were 0.36%,2.70% and 12.38% higher than those of F1 populations at the age of 450 days.The results showed that the average level of variation coefficient of F2 populations’ body weight was decreased 16.54% by compared with F1 populations.The above results showed that the F2 populations had faster growth rate and more neat specifications when compared with F1 populations.2.The genetic variation of mitochondrial DNA D-loop region were analyzed in two breeding generations(F1 and F2)and four wild populations(Hanjiang,Jiujiang,Shishou,Wujiang).The results showed that most of genetic diversity index of wild populations were higher than breeding populations.The genetic diversity index of F1 generations were higher than F2 generations,except for haplotype diversity(Hd).Haplotype analysis,genetic differentiation index(Fst),neighbor-joining phylogenetic trees and haplotype network graph showed that there was a great genetic differentiation between two breeding populations and wild populations(Hanjiang,Jiujiang,Wujiang).The genetic relationship between the Shishou population and breeding populations were close.The above results showed that the genetic diversity of two breeding populations had decreased with the development of breeding programs.The genetic structure of breeding populations had already changed.3.For further analyse the genetic variance in breeding populations,the genetic variation of two breeding populations(F1 and F2)and four wild populations(Hanjiang,Jiujiang,Shishou,Wujiang)were analysed by using multiplex microsatellite PCR methods.Our results showed that the genetic variation of six grass carp populations were relative high and genetic diversity parameters of two breeding populations were lower than wild populations except for average number of alleles(Na).The AMOVA analysis,genetic differentiation index(Fst)analysis,Nei’s genetic distance(Dn)and UPGMA phylogenetic tree showed that six grass carp populations are in low differentiation.The degree of genetic differentiation between two breeding populations and four wild populations was not obvious.The above results showed that the genetic diversity of two breeding populations were decreased compared to four wild populations,but they still have higher level of genetic diversity.The genetic structure of two breeding populations had already changed,but changes was not obviously.4.To screen SNP loci related to growth traits in GH gene for comparison of growth traits in grass carp populations.Nine polymorphic loci were found in this study.Nine loci were not significantly deviated from Hardy-Weinberg equilibrium,and performed moderate polymorphism.The results showed that the body weight,body length and fat content of individuals with the homozygous mutant genotype at SNP2 and SNP3 were significantly higher than wide-type and heterozygous mutant genotype.Similar results were found in fold type combinations analysis.The results showed that the polymorphism of SNP2 and SNP3 in grass carp GH gene had a significant correlation with growth traits,and it can be used as candidate assistant markers for the comparison of growth traits and the analysis of breeding progress.5.Further pave the way for comparison of disease resistance among different grass carp populations.In this study,we evaluated the biological parameters and immune enzymes in the liver of grass carp following A.hydrophila infection and quantified the liver histology using a semi-quantitative system.For the biological parameters,we found that the liver somatic index(LSI)was more sensitive than Fulton’s condition factor(CF)and was significantly decreased at three days post-injection(DPI).At the immune enzyme level,the level of peroxidase(POD),alkaline phosphatase(ALP)and acid phosphatase(ACP)were significantly increased at 1,3,and 5 DPI.Histologically,the results indicated that the changes of liver was more obvious at 3,5,and 7 DPI.