1. The presence of threatened or endangered species often strongly influences management and conservation decisions. Within the Murray–Darling Basin (MDB), Australia, the presence of threatened native fish affects the management and allocation of water resources. In New South Wales, these decisions are currently based on traditional fisheries data and a predictive MaxEnt model. However, it is important to verify the model's predictive power given the implication it may have, but this requires methods with a high detection sensitivity for rare species.
2. Although the use of environmental DNA (eDNA) monitoring, in particular eDNA metabarcoding, achieves a higher detection sensitivity compared with traditional methods, earlier surveys in the MDB have shown that the highly abundant and invasive common carp (Cyprinus carpio) can reduce detection probabilities for rare species. Consequently, a polymerase chain reaction (PCR) blocking primer designed to block the amplification of carp eDNA could increase the detection probabilities for rare native species while simultaneously reducing the required sampling effort and survey costs. Although PCR blocking primers are often used in ancient DNA and dietary studies, no aquatic eDNA metabarcoding study to date has evaluated the potential benefits of using PCR blocking primers.
3. A laboratory and field‐based pilot study was used to address this knowledge gap and assess the impact of a blocking primer, targeting cyprinid fishes (including carp), on the detection probabilities of native species and the minimum sampling effort required.
4. Results showed that the inclusion of the blocking primer increased the detection probabilities for native species by 10–20% and reduced the minimum required sampling effort by 25–50%. These findings provide important insights into possible methods for optimizing eDNA metabarcoding surveys for the detection of rare aquatic species.

中文翻译：

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在环境DNA元条形码调查中改善对稀有本地鱼类物种的检测

1. 受威胁或濒危物种的存在通常会严重影响管理和保护决策。在澳大利亚的默里-达令盆地（MDB）中，受威胁的本地鱼类的存在影响着水资源的管理和分配。在新南威尔士州，这些决定目前基于传统渔业数据和可预测的MaxEnt模型。但是，鉴于模型可能具有的含义，验证模型的预测能力很重要，但这需要对稀有物种具有高检测灵敏度的方法。
2. 尽管与传统方法相比，使用环境DNA（eDNA）监测（尤其是eDNA元条形码）可以实现更高的检测灵敏度，但MDB的早期调查显示，高度丰富且具有侵入性的鲤鱼（Cyprinus carpio）可以降低对虾的检测概率。稀有物种。因此，设计用于阻断鲤鱼eDNA扩增的聚合酶链反应（PCR）阻断引物可以提高稀有天然物种的检测概率，同时减少所需的采样工作量和调查成本。尽管在古代DNA和饮食研究中经常使用PCR封闭引物，但迄今为止，尚无水生eDNA元条形码研究评估使用PCR封闭引物的潜在益处。
3. 一项基于实验室和实地的先导研究被用来解决这一知识鸿沟，并评估针对塞浦路斯鱼类（包括鲤鱼）的封闭引物对本地物种检测概率的影响以及所需的最小采样工作。
4. 结果表明，加入封闭引物可将天然物种的检测概率提高10–20％，并将所需的最低采样工作量降低25–50％。这些发现为优化eDNA元条形码调查以检测稀有水生物种的可能方法提供了重要的见识。