| Large-scale abalone cultivation in China began in the 1980s.In 2016,its total aquaculture production reached nearly 140,000 tons(more than 90%of the world’s),of which Fujian Province accounts for about 80%.But the hypoxia problem during the summer high-temperature period in southern China waters often leads to high mortality of abalone,which restricts the sustainable development of abalone aquaculture industry.Therefore,it is necessary to establish a complete evalution system to assesss tolerance to hypoxia stress of abalone and understand the hypoxia responses of abalone in physiological and molecular levels,laying foundation for cultivating new varieties of abalone with better hypoxia tolerance.In this study,survival,immunity and transcriptional responses of cold water species Haliotis discus hannai(DD)and its hybrid(DF)with H.fulgens(FF)were analyzed,as shown in the following.1.Evaluation of hypoxia resistance ability of DD and DF(1)Survival patterns of DD and DF under hypoxia stress were analyzed.The median lethal hypoxic concentrations of DD and DF were calculated at 20 ℃ and 28 ℃respectively.At 28 ℃,LCso of DD was greater than LC50 of DF,which demonstrating the superiority of DF under hypoxia,thermal stress.(2)The heart rate break points of dissolved oxygen(ABDOs)in abalone was tested,and a new evaluation method was established to measure hypoxia tolerance of abalone based on cardiac performance.Then the applicability and accuracy of the method were verified in DD and DF.The study found that ABDOs of DD and DF were 2.20 mg/L and 2.02 mg/L at 20 ℃,3.25 mg/L and 2.36 mg/L at 25 ℃,3.89 mg/L and 2.49 mg/L respectively,indicating that DF has a better ability to regulate heart rate under extreme hypoxia,especially at high temperature.(3)The oxygen consumption rates of DD and DF during the acute hypoxia stress were measured.At 20℃,there was no significant difference in oxygen consumption rate between DD and DF,but ar 28℃,oxygen consumption rate of DF was significantly higher than that of DD.The results indicated that DF has stronger oxygen uptake capacity under high temperature and low oxygen conditions.2.Immune characteristics of DD and DF under hypoxia stress(1)When injected with Vibrio haryeyi,survival curves showed that 24 h hypoxia stress weakened the immune ability of DF,but had no effect on DD.(2)The effect of hypoxia on total hemocyte count(THC),hemocyte mortality,phagocytosis and reactive oxygen species(ROS)levels were tested in DD and DF.Hemocyte survival rate,the ability to produce ROS and phagocytic activity of DF were found to be stronger than that of DF after 24 h hypoxia stress.However,DF was more effective in the THC,phagocytic activity,and the ability to produce ROS after 96 h hypoxia stress.It showed that weakening effect to immunity system of DD is less under short-term hypoxia stress,and with the extension of processing time,the immune system of DF initiates and responds strongly,exhibiting more excellent immunity.3.Transcriptional analysis of abalone under hypoxia stress(1)Through high-throughput sequencing and and transcriptome(mRNA and lncRNA)analysis,a large number of differentially expressed genes and lncRNAs were identified from gill tissues of DD after 24 h hypoxia stress.They are involved in biological processes such as energy metabolism,DNA synthesis,apoptosis,ion transport,local adhesion,extracellular matrix receptor interaction,salivary secretion,protein/vitamin digestion and absorption,and pathogenic immune stress.In all,the molecular response under hypoxia is to maintain its own aerobic metabolism,control energy consumption,and improve immunity.(2)In PI3K-Akt signaling pathway,six differentially expressed genes were screened,whose expression increases/decreases monotonously with dissolved oxygen.According to their expression pattens,it was speculated that these six genes reveive the hypoxic stimulation signals and transmit to HIF-1 signaling pathway through PI3K/Akt. |
