Growth Performance,hunger Stress And Screening Of Marker Linked To Hypoxia-tolerant In New Strain Of Hypoxia-tolerant Blunt Snout Bream

Blunt snout bream is one of the main breeding species in China and deeply loved by consumers.However,its resistance to low oxygen.In this study,the hypoxic-tolerant breeding lines of blunt snout bream were used as materials to analyze the growth performance at the first and second ages and effects of hunger stress on the gill microstructure and Na⁺/K⁺-ATPase,antioxidant enzyme,and the screening of marker linked to hypoxia-tolerant.This study includes the following three aspects:（1）In order to understand the growth performance of hypoxia-tolerant F₄generation of blunt snout bream,selective group and control group was compared by cut-fin marking method in the same pond during the one and second year at Pudong station and Qingpu station in Shanghai.The results showed that compared to the control group,the growth rate of 1,2 age group faster than 24.7%and 20.9%from the Pudong station.Compared to the control group,the growth rate of 1,2 age group faster than24.4%and 20.9%from the Qingpu station.The results showed that,the growth-performance of hypoxia-tolerant F₄ generation of blunt snout bream was better than others,which was worthy of popularizing.（2）In order to research the effects of different hunger time（0,5,10,15,20,25,and30d）on gills of hypoxia-tolerant F₄ generation of blunt snout bream.The gill microstructure,Na⁺/K⁺-ATPase and antioxidant enzyme of hypoxia-tolerant F₄generation of blunt snout bream was studied by light,scanning electron microscopical and absorptiometry at（25±1.0）℃and dissolved oxygen（7.0±0.5）mg·L^-1.The results showed that with the increase of the hunger time,the activity of Na⁺/K⁺-ATP,SOD and CAT in the hypoxia-tolerant F₄ generation of blunt snout bream was gradually decreased and then restored to normal level after 7 days of re-feeding.Gill microstructure observation showed that the protruding lamella lengths were enlarged,which caused the expansion of the lamella surface area,and the height and volume of the ILCM decreased.After 7 days of re-feeding recovery,the changes in gill morphology were reversed.These results indicated that the hunger stress could seriously disturb the antioxidant system,but fish showed the capacity to alter respiratory surface area in response to hunger.（3）Using the transcriptome data obtained in our laboratory,we selected 10 target genes related to hypoxic tolerance traits,the results of linkage disequilibrium showed that T³⁹⁷C³⁹⁷,T⁷¹⁵G⁷1515 were a set of completed linkage disequilibrium（r²=1）,can be combined into two haplotypes type,namely,haplotypes I(C³⁹⁷G⁷¹⁵)and II(T³⁹⁷T⁷¹⁵).Haplotype analysis revealed that haplotypes I in the control strain was significantly higher than that in new strain of hypoxia-tolerant blunt snout bream,and haplotypesⅡin the control strain was significantly lower than that in new strain of hypoxia-tolerant blunt snout bream.Haplotypes I and II can be combined into three diploid type,namely,diploid typeⅠ(C³⁹⁷C³⁹⁷G⁷¹⁵G⁷¹⁵),diploid typeⅡ(T³⁹⁷T³⁹⁷T⁷¹⁵T⁷¹⁵)and diploid typeⅢ(T³⁹⁷C³⁹⁷T⁷¹⁵G⁷¹⁵).The diploid typeⅡtrain had a significantly（P<0.01）lower critical oxygen tension at which they lost their equilibrium(LOE_crit).The activities of CAT,SOD and Na⁺/K⁺-ATP in diploid typeⅡwere also significantly higher than those in other combinations.When diploid typeⅡtrain were exposed to 4 or7 days of hypoxia,the average protruding lamella heights and mean lamellar area of gills were significantly（P<0.01）smaller than those of diploid typeⅠstrain.These changes resulted in enlarged average interlamellar cell mass（ILCM）height and volume under hypoxia,These showed thatdiploid typeⅡtrain possessed higher hypoxia tolerance than diploid typeⅠstrain.Simultaneously,the blood erythrocyte count and hemoglobin（Hb）concentration of diploid typeⅡstrain increased significantly（P<0.01）compared to diploid typeⅠstrain during hypoxia treatment.The results showed that diploid typeⅡstrain in blunt snout bream Egln2 gene had a significant correlation with hypoxia-tolerant traits,and it might have utility as markers for practical breeding programs for molecular breeding in new strain of hypoxia-tolerant blunt snout bream.