| Grass carp is an important freshwater aquaculture fish in China.As an important environmental factor of aquatic animals,temperature has a serious impact on the growth,development and metabolism of almost all fish.In recent years,with the intensification of the greenhouse effect,the rise of water temperature has become a global problem.As cold-blooded animals,higher water temperature often brings negative effects.The rise of water temperature will reduce the dissolved oxygen in the water body,reduce the biomass of aquatic animals and plants as fish feed resources,and worsen the water quality,which has brought many adverse factors to the normal survival and breeding of fish.In breeding,important economic traits of aquatic animals,such as growth,stress resistance and disease resistance,are quantitative traits,and quantitative genetic correlation research plays an important role in promoting the improvement of important economic traits.In this paper,the growth and heat tolerance of grass carp in three groups of Yangtze River,Pearl River and Heilongjiang were compared and analyzed;The heritability of growth and heat tolerance traits was estimated by establishing a family based on molecular marker paternity identification technology;The differentially expressed genes and pathways under high temperature stress were identified from the transcriptome of the liver and brain tissues of grass carp,and some heat-resistant genes of grass carp were screened.The main findings are as follows:1.In order to explore the growth performance and resistance to high temperature of grass carp in the Yangtze River,Pearl River and Heilongjiang populations,1620individuals of grass carp at different ages from three populations were tested for temperature tolerance.The heat tolerance UTT was used as an indicator to measure the heat tolerance of grass carp,and the corresponding growth and heat tolerance indicators were measured.The variance analysis of growth and heat tolerance was carried out,and the correlation between growth traits and heat tolerance traits was analyzed.The results showed that the heat tolerance of the three populations gradually decreased with the increase of breeding time under the high temperature stress method used in this study,that is,with the increase of individual weight,their tolerance to high temperature gradually weakened.To verify the correlation between growth traits and heat tolerance,Pearson coefficient of SPSS software was used to analyze the correlation between body length,body weight and heat tolerance UTT.For the three groups,the correlation between body length and body weight was the highest,and the correlation coefficient was above 0.900（P<0.01）.The correlation between body weight and heat tolerance of grass carp in three populations was negative.The purpose is to screen out populations with good growth performance and strong heat tolerance,explore the correlation between growth traits and temperature tolerance traits,and lay a research foundation for genetic improvement and family selection of grass carp heat tolerance.2.Based on the paternity identification technology of microsatellite markers,this study analyzed the genetic diversity of 855 individuals of grass carp in the 60-day-old Yangtze River population through 10 pairs of microsatellite markers developed in the laboratory.Statistical analysis revealed significant differences in the contribution of parents to their offspring.Through the genetic diversity analysis,the number of effective alleles in the offspring increased slightly.The frequency of invalid alleles at10 marker sites was less than 0.02.Three sets of multiple PCR systems were designed,and the pedigree information of 55 alternative parents and 800 progeny were determined.The 800 progeny could successfully match the correct parents,and the success rate of parental allocation could reach 100%.Based on pedigree information,the heritability of growth traits and heat resistance traits of 60-day-old Yangtze River grass carp was estimated using animal models.The heritability of body weight was0.326,and the heritability of body length was 0.314,belonging to medium heritability.The heritability of heat tolerance trait is 0.106,belonging to low heritability.3.In order to investigate the molecular regulation mechanism of grass carp under high temperature stress and to screen out the genes related to heat tolerance in grass carp,transcriptome data of grass carp brain and liver tissues under high temperature were analyzed by RNA-seq.42.49 GB and 42.57 GB of data were obtained from six liver libraries and six brain libraries constructed,and a total of 2534 differentially expressed genes（DEGs）were identified in liver tissues The KEGG pathway analysis revealed that the endoplasmic reticulum and peroxisome proliferator-activated receptor signaling pathways in the c AMP signaling pathway,apoptosis,Ca2+pathway,lipid metabolism The expression of genes related to metabolic and immune pathways,such as the endoplasmic reticulum and peroxisome proliferator-activated receptor signaling pathways,apoptosis,Ca2+pathway,lipid metabolism,and protein processing were significantly different(P<0.05.This study showed that high temperature promoted lipid metabolism,decreased fatty acid synthesis,and damaged the immune system in grass carp,and analyzed the molecular regulation of heat stress in grass carp,which provided valuable information for healthy breeding under high temperature. |
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