Large parasites in a crowded space: variation in prevalence and volumetric effects of <em>Sarcotaces arcticus</em> (Collett, 1874) in two host rockfish (<em>Sebastes</em> spp.) species.

Sarcotaces arcticus (Collett, 1874) is a relatively large, internal parasitic copepod that infects many marine fishes. Although its large size suggests it may have a negative effect on host reproduction by reducing space available in the abdominal cavity (i.e., volumetric effect), such quantitative aspects of host-parasite relationships for S. arcticus have never been documented. We compared the prevalence and the ratio of live to dead parasites among sizes and sexes of two species of rockfish hosts (Sebastes ciliatus, Tilesius, 1813, dark rockfish; and Sebastes variabilis, Pallas, 1814, dusky rockfish) and quantified the reduction of internal space available in infected hosts. Samples were collected in southeast Alaskan waters where the two host rockfish species coexist in sympatry. Both total prevalence and prevalence of live S. arcticus were significantly higher in S. variabilis compared to S. ciliatus, because of higher prevalence in female S. variabilis. The relationship between bo..., To assess the prevalence and effects on internal volume of hosts of S. arcticus, we surveyed two species of rockfish: S. variabilis and S. ciliatus. Sebastes ciliatus and S. variabilis are sister species that are commonly caught in the same areas. Both species are pelagic, occur in large aggregations, and feed on pelagic crustaceans in the water column. They are sympatric and syntopic in the areas we surveyed, such that fishing yields a mix of both species and sexes, and the depth at which both species are caught does not differ. We caught both species via hook and line in Frederick Sound, near Admiralty Island, AK, USA (56°57′14.76″ N, 134°10′36.19″ W). We were not able to collect individuals from the smallest size class (&lt;240 mm TL; ages 1–4 yr) of either host fish species. This study focuses on individuals larger than about 240 mm TL, which are the smallest individuals available in the large aggregations where we fished. Study system We caught a total of 182 S. ciliatus and 135 S...., , # Large parasites in a crowded space: variation in prevalence and volumetric effects of *Sarcotaces arcticus* (Collett, 1874) in two host rockfish (*Sebastes* spp.) species [https://doi.org/10.5061/dryad.1ns1rn93z](https://doi.org/10.5061/dryad.1ns1rn93z) ## Description of the data and file structure Large parasites in a crowded space: variation in prevalence and volumetric effects of *Sarcotaces arcticus* in two host rockfish (*Sebastes* spp.) species ### Files and variables #### File: Sarcotaces_arcticus_dataset_Sept_2025.xlsx | TAB: All Fish Data, Columns | Description | | :----------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------- | | Data collected from July 7–10, 2017 | ...,# 拥挤空间中的大型寄生虫：两种岩鱼宿主（平鲉属*Sebastes* spp.）体内北极肉虱（*Sarcotaces arcticus*，Collett, 1874）的感染率与体积效应变异 [https://doi.org/10.5061/dryad.1ns1rn93z](https://doi.org/10.5061/dryad.1ns1rn93z) ## 数据集概述 北极肉虱（*Sarcotaces arcticus*，Collett, 1874）是一类体型较大的体内寄生桡足类（Copepod），可感染多种海洋鱼类。尽管其体型较大，推测可能通过挤占宿主腹腔可用空间（即体积效应）对宿主繁殖产生负面影响，但目前尚无针对该寄生虫与宿主间这种量化寄生关系的研究记录。 本研究针对两种岩鱼宿主——裸平鲉（*Sebastes ciliatus*，Tilesius, 1813，又称暗色岩鱼）及变色平鲉（*Sebastes variabilis*，Pallas, 1814，又称暗灰岩鱼）的不同体长组与性别组，比较了其北极肉虱感染率及寄生虫存活/死亡比例，并量化了感染宿主的腹腔可用空间缩减量。样本采集于阿拉斯加东南部海域，该区域两种岩鱼宿主同域分布。相较于裸平鲉，变色平鲉的总感染率及活北极肉虱感染率均显著更高，这一差异源于变色平鲉雌性个体的感染率更高。[原文此处内容截断] 为评估北极肉虱的感染率及其对宿主腹腔体积的影响，本研究针对两种岩鱼宿主展开调查。裸平鲉与变色平鲉为姊妹物种，二者常被同时捕捞于同一海域。两种岩鱼均为远洋性物种，常聚集成大群，以水层中的远洋甲壳类为食。在本研究的调查区域内，二者同域且同生境分布，因此捕捞所得样本同时包含两种鱼类的不同性别个体，且两种岩鱼的捕捞水深无显著差异。 本研究于美国阿拉斯加州阿德默勒尔蒂岛附近的弗雷德里克桑德海域，通过手竿钓获了两种岩鱼样本，采样坐标为北纬56°57′14.76″，西经134°10′36.19″。我们未能采集到两种宿主岩鱼最小体长组（总长度<240mm TL；年龄1~4龄）的个体。本研究仅针对总长度约240mm TL以上的个体展开分析，这类个体也是本次捕捞作业所获大群样本中的最小个体。 ### 研究系统 本次作业共采集到182尾裸平鲉与135尾[原文此处内容截断] ## 数据与文件结构说明 ### 文件与变量 #### 文件：Sarcotaces_arcticus_dataset_Sept_2025.xlsx | 表格：All Fish Data（所有鱼类数据），列信息 | 详细描述 | | :----------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------- | | 数据采集于2017年7月7日至10日 | ... |