Wynne James W, English Chloe J, Vannetti Stefania M, Rigby Megan, Quezada-Rodriguez Petra R, Knüsel Ralph, Huynh Christine, Schmidt-Posthaus Heike
CSIRO Agriculture and Food, Hobart, Tasmania, Australia.
School of Environment, The University of Queensland, Brisbane, Queensland, Australia.
J Fish Dis. 2025 Mar;48(3):e14061. doi: 10.1111/jfd.14061. Epub 2024 Dec 5.
Nodular gill disease (NGD) is a serious proliferative gill condition that affects farmed salmonids, particularly in Europe. While the cause of NGD remains unknown (and maybe multifactorial), various amoebae are often isolated from the gills of affected fish and can in some cases be seen associated with lesions by histopathology. The present study aimed to quantify the abundance of different amoeba species directly from the gills of rainbow trout affected by NGD and healthy controls. An 18S rRNA amplicon metagenomic approach was employed to profile the diversity and abundance of micro-eukaryotes (including amoebae) while suppressing the amplification of host DNA using a salmonid-specific C3 spacer blocking primer. The 18S rRNA metagenomics approach identified a diversity of micro-eukaryotes on the gills of rainbow trout, including the phylum's Amoebozoa, Diatomea, Platyhelminthes and Ciliophora. Rainbow trout clinically affected by NGD had a significantly higher abundance of a specific sequence (zOTU2) classified as Vannella sp. compared to healthy controls. A quantitative PCR assay was then developed and validated which accurately quantified the abundance of this Vannella sp. sequence from a NGD outbreak in a Swiss rainbow trout farm. Additional PCR and Sanger sequencing analysis of the zOTU2 sequence demonstrated that this sequence is most likely derived from Vannella mustalahtiana. Our study highlights the potential role of Vannella mustalahtiana in NGD in Switzerland and further describes a specific and validated diagnostic PCR assay for accurate detection of this Vannella species.
结节性鳃病（NGD）是一种严重的增殖性鳃部疾病，影响养殖的鲑科鱼类，在欧洲尤为常见。虽然NGD的病因尚不清楚（可能是多因素的），但在受影响鱼类的鳃中经常分离出各种变形虫，在某些情况下，通过组织病理学可以看到它们与病变有关。本研究旨在直接量化受NGD影响的虹鳟鱼和健康对照鱼鳃中不同变形虫物种的丰度。采用18S rRNA扩增子宏基因组学方法来分析微真核生物（包括变形虫）的多样性和丰度，同时使用鲑科特异性C3间隔阻断引物抑制宿主DNA的扩增。18S rRNA宏基因组学方法鉴定出虹鳟鱼鳃上存在多种微真核生物，包括变形虫门、硅藻门、扁形动物门和纤毛虫门。临床受NGD影响的虹鳟鱼中，一种被归类为Vannella sp.的特定序列（zOTU2）的丰度显著高于健康对照鱼。随后开发并验证了一种定量PCR检测方法，该方法能准确量化瑞士虹鳟鱼养殖场NGD疫情中这种Vannella sp.序列的丰度。对zOTU2序列进行的额外PCR和桑格测序分析表明，该序列很可能源自Vannella mustalahtiana。我们的研究突出了Vannella mustalahtiana在瑞士NGD中的潜在作用，并进一步描述了一种用于准确检测该Vannella物种的特异性且经过验证的诊断性PCR检测方法。
