Effect of diurnal oxygen variation on gene expression in Pacific white shrimp reared in green water system tanks

World aquaculture production of the Pacific white shrimp (Litopenaeus vannamei) is estimated to account for 80% of the total shrimp produce worldwide. The global demand for shrimp has driven the industry to utilize and rely on semi-intensive and intensive shrimp systems. In the United States, Pacific white shrimp production can take place in semi-intensive earthen ponds, recirculating aquaculture systems (RAS), biofloc technology and green water. In this study, the effects of lowering dissolved oxygen conditions in outdoor green water tanks on global gene expression is examined. Tissue samples from the gill and intestine were collected for gene expression analysis via RNA sequencing. Among all comparisons, RNA sequencing revealed the up-regulation of a single gene: hydroxyacid oxidase 1 gene. The HOA1 gene was found to be 7-fold higher in the intestine sample at the medium aeration level compare to that of the high (control) level. The HAO1 gene, also known as glycolate oxidase 1 (GOX1) is a gene related to the 2-hydroxyacid oxidase enzyme that is part of the oxidoreductase family and plays a role in glyoxylate and dicarboxylate metabolism. The identification of a single differentially expressed gene across all analyzed samples suggests that Pacific white shrimp exposed to lowering dissolved oxygen set points does not induce global changes in gene expression at these levels. Twelve (800 L) round tanks were stocked each with 35 shrimp (1.99 ± 0.06g) and reared in 15 ppt green water system tanks for 6 weeks. Four of the tanks were aerated at 0.25 cubic feet per second (cfs; low), four at 0.35 cfs (medium) and four at 0.7 cfs (high). The experiment was terminated 42 days after stocking, when two shrimp per tank were randomly collected, and gill (fourth gill filament from one side) and intestine were extracted and preserved in DNA/RNA shield (ZYMO Research, Irvine, CA, USA) for RNA sequencing.

太平洋白对虾（Litopenaeus vannamei）的全球水产养殖产量约占全球对虾总产量的80%。全球对虾需求推动养殖产业采用并依赖半精养与精养对虾养殖系统。在美国，太平洋白对虾养殖可采用半精养土塘、循环水养殖系统（recirculating aquaculture systems, RAS）、生物絮团技术以及绿水养殖模式。本研究探讨了室外绿水养殖箱中溶解氧设定值降低对太平洋白对虾全局基因表达的影响。研究人员采集鳃与肠道组织样本，通过RNA测序（RNA Sequencing）开展基因表达分析。在所有比对组别中，RNA测序仅鉴定出单个上调基因：羟酸氧化酶1（hydroxyacid oxidase 1）基因。研究发现，相较于高曝气（对照组）水平，中等曝气条件下肠道样本中的HOA1基因表达量上调7倍。HAO1基因又称乙醇酸氧化酶1（glycolate oxidase 1, GOX1），属于氧化还原酶家族的2-羟酸氧化酶编码基因，参与乙醛酸与二羧酸代谢过程。在所有分析样本中仅检出单个差异表达基因，这表明暴露于降低溶解氧设定值的太平洋白对虾，在本实验设置的浓度范围内不会引发全局基因表达变化。本实验共设置12个容积为800升的圆形养殖箱，每箱放养35尾体重为1.99±0.06g的对虾，在盐度为15ppt的绿水养殖系统中饲养6周。其中4个水箱以0.25立方英尺每秒（cfs；低曝气组）曝气，4个以0.35 cfs（中曝气组）曝气，剩余4个以0.7 cfs（高曝气组）曝气。实验于放苗后42天终止，随机采集每箱2尾对虾，提取其鳃组织（单侧第四鳃丝）与肠道组织，保存于DNA/RNA保护液（DNA/RNA shield，ZYMO Research，美国加利福尼亚州欧文市）中，用于后续RNA测序。