1. Many aquatic organisms can consume parasite larvae, thus hampering parasite transmission; however, information about feeding on them in the presence of an alternative prey remains scarce. When having a food choice, predators may decrease parasite consumption, therefore, it is important to assess the role of parasites in the diet of predators in natural communities with different types of prey available. Our study aims to test whether common freshwater cyclopoids feed on trematode free‐living stages (cercariae) when an alternative food source is present.
2. We experimentally studied ingestion rates of cyclopoids Macrocyclops distinctus fed with cercariae of trematode Diplostomum pseudospathaceum, a common and harmful parasite of freshwater fishes, and ciliates Paramecium caudatum (an alternative prey, known as suitable food for copepods). First, the feeding response of cyclopoids to different densities of each prey was studied. Then, feeding selectivity in the mixtures of cercariae and ciliates was tested.
3. Feeding rates of cyclopoids increased with prey densities (both ciliates and cercariae) but almost stopped growing at high prey densities, which indicated saturation (Holling type II functional response). In most cases, cyclopoids consumed cercariae at higher rates than ciliates. Maximum ingestion rates estimated from the obtained curves were 37 cercariae ind⁻¹ hr⁻¹ and 17 ciliate ind⁻¹ hr⁻¹.
4. When exposed to prey mixtures, cyclopoids fed on cercariae selectively. When cercariae were offered to cyclopoids at concentrations exceeding the saturation level, the ingestion of ciliates remained constantly low at all ciliate densities. In contrast, the ingestion of cercariae increased with rising cercariae densities even when ciliates were presented ad libitum, decreasing only at very high prey densities. Possible reasons of such feeding preferences are discussed.
5. Our study demonstrated that cyclopoids may prefer to feed on cercariae when there is an alternative food choice and can ingest cercariae at high rates. These experimental results could be extended to natural communities, suggesting that cyclopoids can reduce the transmission of parasites and contribute to the incorporation of parasite production in food webs of lentic ecosystems.

中文翻译：

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摆线虫有选择地以寄生虫的自由生长期为食

1. 许多水生生物可以食用寄生虫的幼虫，从而阻碍了寄生虫的传播。然而，关于在另类猎物面前觅食它们的信息仍然很少。选择食物时，捕食者可能会减少寄生虫的消费，因此，重要的是评估寄生虫在具有不同类型猎物的自然社区中的饮食中的作用。我们的研究旨在测试在存在替代性食物来源时，常见的淡水摆线虫是否以吸虫生活阶段（尾c）为食。
2. 我们实验研究的cyclopoids摄取率Macrocyclops distinctus用吸虫尾蚴馈送Diplostomum pseudospathaceum，淡水鱼的一个共同的和有害的寄生虫，和纤毛虫草履虫（替代猎物，被称为合适的食品桡足类）。首先，研究了摆线对不同猎物密度的摄食反应。然后，测试了尾c和纤毛虫的混合物中的进料选择性。
3. 摆线虫的摄食率随猎物密度（纤毛虫和尾c）而增加，但在高猎物密度时几乎停止生长，这表明其饱和（Holling II型功能性反应）。在大多数情况下，摆线虫消耗尾c的比率高于纤毛虫。从获得的曲线估计的最大摄取率分别为37尾蚴IND ^-1 小时^-1和17纤毛虫IND ^-1 小时^-1。
4. 当暴露于猎物混合物中时，摆线虫有选择地以尾c为食。当将尾aria以超过饱和水平的浓度提供给摆线体时，在所有纤毛密度下，纤毛的摄入量始终保持低水平。相反，即使随意出现纤毛虫，尾c的摄入也随尾c密度的增加而增加，仅在非常高的猎物密度时才减少。讨论了这种进食偏好的可能原因。
5. 我们的研究表明，当有其他食物可供选择时，摆线虫可能更喜欢以尾c为食，并且可以以很高的速度摄入尾c。这些实验结果可以扩展到自然界，这表明摆线体可以减少寄生虫的传播，并有助于将寄生虫的生产纳入透镜体生态系统的食物网。