Abstract The fat greenling, Hexagrammos otakii, is an emerging aquaculture species and is being evaluated for production in recirculating aquaculture systems (RAS). To better understand the tolerance of H. otakii to varying environmental salinity in actual aquaculture operations, the effects of salinity on survival, growth, hematological parameters, gill microstructure and gill transcriptome were investigated. Juvenile H. otakii (22.0± 1.8 g; 11.2 ± 0.7 cm) were reared at different salinities, 6.7 ± 0.1 PSU (7 PSU), 12.3 ± 0.1 PSU (12 PSU), 18.2 ± 0.1 PSU (18 PSU), 23.9 ± 0.6 PSU (24 PSU), and 28.9 ± 0.8 PSU (29 PSU) in triplicated RASs for five weeks, and the impacts of salinity on these endpoints were evaluated. Fish in the 7 PSU group exhibited significantly lower survival, final weight, feed conversion ratio, and specific growth rate than fish in other treatments. While no statistically significant differences were found among mean white blood cell counts, red blood cell counts and hemoglobin concentrations, mean corpuscular volume was significantly lower in the 7 PSU group than in other groups. At the histological level, there were smaller numbers and smaller volume of mitochondria-rich cells in the 7 PSU group, and the numbers of pavement cells and mucous cells were significantly higher than in other groups. Transcriptome sequencing for a sample of individuals from the 7 PSU, 18 PSU and 29 PSU groups indicated that gene expression in the gills of H. otakii differed significantly among groups. Gene ontology (GO) enrichment showed differential expression between the 7 PSU and 29 PSU groups for seven genes with activities as neurotransmitter transmembrane transporters and neurotransmitter: sodium symporters. Comparing to the 18 PSU group, 16 genes with activities in gas or oxygen transport were down-regulated in the 7 PSU group. No such differences in expression of gas transport genes was found between the 18 PSU and 29 PSU groups. Overall, our exploratory transcriptome analysis suggested that fish in the low-salinity 7 PSU group exhibited high gene expression in the osmoregulation and gas transport pathways. Our results at the histological and gene expression levels suggest why rearing juvenile H. otakii in salinities of 12–29 PSU is optimal for commercial aquaculture production.

中文翻译：

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盐度对肥菖蒲生长、血液学参数、鳃微结构和转录组的影响

摘要 肥鱼 Hexagrammos otakii 是一种新兴的水产养殖品种，正在对循环水产养殖系统 (RAS) 的生产进行评估。为了更好地了解 H. otakii 在实际水产养殖操作中对不同环境盐度的耐受性，研究了盐度对存活、生长、血液学参数、鳃微观结构和鳃转录组的影响。H. otakii 幼鱼 (22.0± 1.8 g; 11.2 ± 0.7 cm) 在不同盐度下饲养，6.7 ± 0.1 PSU (7 PSU)、12.3 ± 0.1 PSU (12 PSU)、18.2 ± 0.1 PSU (18 PSU)、± 0.6 PSU (24 PSU) 和 28.9 ± 0.8 PSU (29 PSU) 在三重 RAS 中持续五周，并评估了盐度对这些终点的影响。7 PSU 组中的鱼的存活率、最终体重、饲料转化率、和比其他处理中的鱼的特定增长率。虽然在平均白细胞计数、红细胞计数和血红蛋白浓度之间没有发现统计学上的显着差异，但 7 PSU 组的平均红细胞体积显着低于其他组。在组织学水平上，7 PSU组富含线粒体的细胞数量较少，体积较小，而铺路细胞和粘液细胞的数量明显高于其他组。来自 7 个 PSU、18 个 PSU 和 29 个 PSU 组的个体样本的转录组测序表明，H. otakii 鳃中的基因表达在各组之间存在显着差异。基因本体论 (GO) 富集显示 7 个 PSU 组和 29 个 PSU 组之间存在差异表达，其中 7 个基因具有神经递质跨膜转运蛋白和神经递质：钠同向转运蛋白的活性。与18 PSU组相比，7 PSU组中有16个具有气体或氧气运输活性的基因下调。在 18 个 PSU 和 29 个 PSU 组之间没有发现气体转运基因表达的这种差异。总体而言，我们的探索性转录组分析表明，低盐度 7 PSU 组中的鱼在渗透调节和气体运输途径中表现出高基因表达。我们在组织学和基因表达水平上的结果表明，为什么在 12-29 PSU 的盐度中饲养 H. otakii 幼鱼最适合商业水产养殖生产。与18 PSU组相比，7 PSU组中有16个具有气体或氧气运输活性的基因下调。在 18 个 PSU 和 29 个 PSU 组之间没有发现气体转运基因表达的这种差异。总体而言，我们的探索性转录组分析表明，低盐度 7 PSU 组中的鱼在渗透调节和气体运输途径中表现出高基因表达。我们在组织学和基因表达水平上的结果表明，为什么在 12-29 PSU 的盐度中饲养 H. otakii 幼鱼最适合商业水产养殖生产。与18 PSU组相比，7 PSU组中有16个具有气体或氧气运输活性的基因下调。在 18 个 PSU 和 29 个 PSU 组之间没有发现气体转运基因表达的这种差异。总体而言，我们的探索性转录组分析表明，低盐度 7 PSU 组中的鱼在渗透调节和气体运输途径中表现出高基因表达。我们在组织学和基因表达水平上的结果表明，为什么在 12-29 PSU 的盐度中饲养 H. otakii 幼鱼最适合商业水产养殖生产。我们的探索性转录组分析表明，低盐度 7 PSU 组中的鱼在渗透调节和气体运输途径中表现出高基因表达。我们在组织学和基因表达水平上的结果表明，为什么在 12-29 PSU 的盐度中饲养 H. otakii 幼鱼最适合商业水产养殖生产。我们的探索性转录组分析表明，低盐度 7 PSU 组中的鱼在渗透调节和气体运输途径中表现出高基因表达。我们在组织学和基因表达水平上的结果表明，为什么在 12-29 PSU 的盐度中饲养 H. otakii 幼鱼最适合商业水产养殖生产。