The parasitic ciliate Ichthyophthirius multifiliis has a low host specificity eliciting white spot disease (WSD) in a wide range of freshwater fishes worldwide. The parasite multiplies rapidly whereby the infection may reach problematic levels in a host population within a few days. The parasite targets both wild and cultured fish but the huge economic impact of the protozoan is associated with mortality, morbidity and treatment in aquacultural enterprises. We have investigated the potential for genetic selection of WSD‐resistant strains of rainbow trout. Applying the DNA typing system Affymetrix^® and characterizing the genome of the individual fish by use of 57,501 single nucleotide polymorphisms (SNP) and their location on the rainbow trout chromosomes, we have genetically characterized rainbow trout with different levels of natural resistance towards WSD. Quantitative trait loci (QTL) used for the selection of breeders with specific markers for resistance are reported. We found a significant association between resistance towards I. multifiliis infection and SNP markers located on the two specific rainbow trout chromosomes Omy 16 and Omy 17. Comparing the expression of immune‐related genes in fish—with and without clinical signs—we recorded no significant difference. However, trout surviving the infection showed high expression levels of genes encoding IgT, T‐cell receptor TCRβ, C3, cathelicidins 1 and 2 and SAA, suggesting these genes to be associated with protection.

中文翻译：

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与虹鳟 Oncorhynchus mykiss 对寄生纤毛虫 Ichthyophthirius multifiliis 的抗性相关的数量性状位点 (QTL)。

寄生性纤毛虫Ichthyophthirius multifiliis 的宿主特异性较低，可在全世界多种淡水鱼中引发白斑病 (WSD)。寄生虫迅速繁殖，几天内宿主群体中的感染可能达到有问题的水平。这种寄生虫以野生和养殖鱼类为目标，但原生动物的巨大经济影响与水产养殖企业的死亡率、发病率和治疗有关。我们研究了 WSD 抗性虹鳟鱼品系的遗传选择潜力。通过应用 DNA 分型系统 Affymetrix ^®并利用 57,501 个单核苷酸多态性 (SNP) 及其在虹鳟鱼染色体上的位置来表征个体鱼的基因组，我们对虹鳟鱼具有不同水平的 WSD 天然抗性进行了遗传表征。报告了用于选择具有特定抗性标记的育种者的数量性状基因座（QTL）。我们发现对多子线虫感染的抵抗力与位于两条特定虹鳟鱼染色体 Omy 16 和 Omy 17 上的 SNP 标记之间存在显着关联。比较鱼类中免疫相关基因的表达（有无临床症状），我们没有记录到显着的相关性。不同之处。然而，感染后幸存的鳟鱼显示出编码 IgT、T 细胞受体 TCRβ、C3、抗菌素 1 和 2 以及 SAA 的基因的高表达水平，表明这些基因与保护有关。