Predation risk for animal migrants can be impacted by physical condition. Although size- or condition-based selection is often observed, observing infection-based predation is rare due to the difficulties in assessing infectious agents in predated samples. We examined predation of outmigrating sockeye salmon (Oncorhynchus nerka) smolts by bull trout (Salvelinus confluentus) in south-central British Columbia, Canada. We used a high-throughput quantitative polymerase chain reaction (qPCR) platform to screen for the presence of 17 infectious agents found in salmon and assess 14 host genes associated with viral responses. In one (2014) of the two years assessed (2014 and 2015), the presence of infectious haematopoietic necrosis virus (IHNv) resulted in 15–26 times greater chance of predation; in 2015 IHNv was absent among all samples, predated or not. Thus, we provide further evidence that infection can impact predation risk in migrants. Some smolts with high IHNv loads also exhibited gene expression profiles consistent with a virus-induced disease state. Nine other infectious agents were observed between the two years, none of which were associated with increased selection by bull trout. In 2014, richness of infectious agents was also associated with greater predation risk. This is a rare demonstration of predator consumption resulting in selection for prey that carry infectious agents. The mechanism by which this selection occurs is not yet determined. By culling infectious agents from migrant populations, fish predators could provide an ecological benefit to prey.

动物迁徙的捕食风险会受到身体状况的影响。尽管经常会观察到基于大小或条件的选择，但由于难以评估掠夺性样本中的传染原，因此很少观察到基于感染的掠食性。我们研究了由鳟鱼（Salvelinus confluentus）移出的红鲑（Oncorhynchus nerka）软体动物的捕食）位于加拿大不列颠哥伦比亚省中南部。我们使用了高通量定量聚合酶链反应（qPCR）平台来筛选鲑鱼中发现的17种传染原，并评估14种与病毒反应相关的宿主基因。在评估的两年（2014年和2015年）中的一个（2014年），传染性造血坏死病毒（IHNv）的存在导致被捕食的机会增加了15-26倍；在2015年之前，所有样本中都没有IHNv。因此，我们提供了进一步的证据，证明感染会影响移民的捕食风险。一些具有高IHNv负荷的软体动物也表现出与病毒诱导的疾病状态一致的基因表达谱。在这两年之间，还观察到其他九种传染病原体，它们均与鳟鱼的选择增加无关。在2014年，感染因子的丰富还与更大的捕食风险相关。这是食肉动物消费的罕见展示，导致选择了携带传染性因子的猎物。尚未确定进行此选择的机制。通过从移徙人口中剔除传染病，鱼类捕食者可以为猎物提供生态效益。