1. Local extinctions break species interactions and have cascading effects throughout ecosystems; parasites are often severely affected. The European bitterling, Rhodeus amarus, is a cyprinid fish that parasitizes unionid mussels by laying eggs into the mussel gill cavity, where embryos develop and emerge as active juveniles; this relationship is obligatory for the bitterling.
2. This article describes a field experiment aimed at averting the secondary extinction of the European bitterling after a complete die-off of a freshwater mussel community, as a result of habitat destruction.
3. Approximately 5,000 unionid mussels were reintroduced within the short time frame in which the remnant bitterling population was still present at the site. Mussel survival was high, and bitterling resumed reproduction, with vigorous courtship observed within 24 hours of mussel release. Recruitment was successful, as evidenced by increased occupancy, densities, and relative frequencies in the fish assemblage. The frequency of sub-adults and young-of-the-year changed from 0% before mussel reintroduction to 80% a year later, and 50% 2 years later, when young-of-the-year contributed to about half of the young fish. No bitterling were observed at two control sites where mussels were not reintroduced.
4. This study exemplifies how the timely restitution of affiliate species can avert co-extinction. It also shows how the conservation of the bitterling within its historical distribution range can serve mussel conservation, including species that although not legally protected, are important keystone species and ecosystem engineers, shaping the structure and function of a broad range of freshwater habitats.

中文翻译：

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避免共同灭绝：成功的贻贝易位拯救了濒临灭绝的欧洲苦口鱼 Rhodeus amarus

1. 局部灭绝破坏了物种之间的相互作用，并对整个生态系统产生了连锁效应；寄生虫往往受到严重影响。欧洲苦鱼，Rhodeus amarus，是一种鲤科鱼类，通过在贻贝鳃腔中产卵来寄生于贻贝，胚胎在那里发育并作为活跃的幼鱼出现；这种关系是强制性的苦涩。
2. 本文描述了一项田间试验，该试验旨在避免淡水贻贝群落因栖息地破坏而完全灭绝后再次灭绝。
3. 大约 5,000 只贻贝在很短的时间内被重新引入，其中残留的苦口鱼种群仍然存在于现场。贻贝的存活率很高，苦味恢复繁殖，在贻贝释放后 24 小时内观察到强烈的求爱。招募是成功的，鱼群中的占有率、密度和相对频率增加就证明了这一点。亚成体和幼体的频率从重新引入贻贝前的 0% 变为一年后的 80% 和 2 年后的 50%，当年幼体贡献了大约一半的幼体鱼。在没有重新引入贻贝的两个对照地点没有观察到苦味。
4. 这项研究举例说明了及时恢复附属物种如何避免共同灭绝。它还展示了在其历史分布范围内保护苦鲆如何为贻贝保护服务，包括虽然不受法律保护的物种，但它们是重要的关键物种和生态系统工程师，塑造了广泛的淡水栖息地的结构和功能。