Stable isotope analyses of carbon and nitrogen (δ¹³C and δ¹⁵N) are useful for elucidating consumer relationships of free-living organisms, as carbon isotopes indicate dietary carbon sources and incremental increases in nitrogen isotopic enrichment are correlated with increases in trophic position. However, host–parasite relationships are more difficult to interpret using isotopes, as data from different host–parasite systems rarely show any consistent pattern. This inconsistency of pattern reflects the complexity of host–parasite relationships, but also the scarcity of data from a diverse assemblage of host–parasite systems. We present stable isotope data from a host–parasite system including 2 ecologically contrasting helminths, an acanthocephalan (Filisoma filiformis) and a digenetic trematode (Enenterum sp.), which co-occur in the intestine of the same marine fish (Kyphosus bigibbus), the diet of which consists almost exclusively of macroalgae. We obtained δ¹³C and δ¹⁵N data from K. bigibbus muscle, stomach contents, and pooled infrapopulations of Enenterum sp. and F. filiformis. Consistent with other isotope studies including acanthocephalans, F. filiformis was depleted in δ¹³C and δ¹⁵N relative to K. bigibbus. Although Enenterum sp. exhibited values for δ¹³C similar to those for F. filiformis, they were enriched in δ¹⁵N relative to the acanthocephalan, with a signature similar to that of K. bigibbus. These findings are discussed within a host–ecosystem context, highlighting the importance of considering species-specific biology when interpreting host–parasite relationships using stable isotopes. Our study adds to the growing body of literature indicating that absorptive feeders, such as acanthocephalans, are typically depleted in δ¹³C and δ¹⁵N relative to their hosts, whereas trematodes, with a greater diversity of feeding opportunities, exhibit a wide variety of isotopic signatures across life stage and different host–parasite systems.

碳和氮（δ ¹³ C 和 δ ¹⁵ N）的稳定同位素分析有助于阐明自由生物的消费者关系，因为碳同位素表明膳食碳源，并且氮同位素富集的增量增加与营养位置的增加相关。然而，使用同位素更难以解释宿主-寄生虫关系，因为来自不同宿主-寄生虫系统的数据很少显示出任何一致的模式。这种模式的不一致反映了宿主-寄生虫关系的复杂性，但也反映了来自多种宿主-寄生虫系统组合的数据稀缺性。我们提供了来自宿主-寄生虫系统的稳定同位素数据，包括 2 种生态对比鲜明的蠕虫，一种棘头虫（Filisoma filiformis) 和一种双基因吸虫 ( Enenterum sp.)，它们共同出现在同一海鱼 ( Kyphosus bigibbus )的肠道中，其饮食几乎完全由大型藻类组成。我们得到的δ ¹³ C和δ ^15个从N个数据K. bigibbus肌肉，胃内容物，并汇集infrapopulations Enenterum藻。和F. 丝状菌。与包括棘头动物在内的其他同位素研究一致，F. filiformis相对于K. bigibbus 的δ ¹³ C 和 δ ¹⁵ N被耗尽。虽然Enenterum sp。显示值 δ ¹³C 与F. filiformis相似，它们相对于棘头动物富含 δ ¹⁵ N，具有与K. bigibbus相似的特征。这些发现在宿主-生态系统背景下进行了讨论，强调了在使用稳定同位素解释宿主-寄生虫关系时考虑物种特异性生物学的重要性。我们的研究增加了越来越多的文献，表明吸收性饲养者，例如棘头动物，相对于其宿主通常在 δ ¹³ C 和 δ ¹⁵ N 中耗尽，而吸虫具有更多样化的喂养机会，表现出各种各样的跨生命阶段和不同宿主-寄生虫系统的同位素特征。