In freshwater ecosystems, invasive salmonid fishes can have a significant impact on native fish species. Detecting the invasion and its negative effects is critical for the conservation of native fish communities. We examined the species composition and seasonal changes in the freshwater fish community, including salmonids, on the Kamikawa Plain, Hokkaido Island, Japan, using environmental DNA (eDNA) metabarcoding. We detected 23 fish species in 176 samples collected from 16 sites over 12 months (October 2018 – August 2019). Between 11 and 20 species were detected at each site, including five native salmonids (Oncorhynchus masou, Oncorhynchus keta, Parahucho perryi, Salvelinus leucomaenis leucomaenis and Salvelinus malma krascheninnikova). The invasive alien rainbow trout Oncorhynchus mykiss was detected at all 16 sites and it was the most commonly detected salmonid. Although we found no obvious competitive exclusion of native salmonids by rainbow trout in the study area, the invasive species occurred more often and at more sites than any of the natives. We also determined the occurrence and seasonal changes in the fish community, classified as native salmonids, invasive rainbow trout, Cypriniformes and other benthic fishes. There were fewer species overall in winter, but the sites with higher species richness in winter were on the lower reaches of the river. In addition, we detected domestic invaders, such as the topmouth gudgeon, Pseudorasbora parva, although they were less prevalent than rainbow trout. These results show the effectiveness of eDNA metabarcoding, which can be used for surveying species richness at an ecosystem scale. In particular, the detection of the early stages of establishment and spread of invasive species can be achieved by eDNA monitoring.

中文翻译：

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环境基因揭示了虹鳟入侵后日本北海道岛的鱼类群落

在淡水生态系统中，入侵性鲑鱼可能会对本地鱼类产生重大影响。发现入侵及其负面影响对于保护本地鱼类群落至关重要。我们使用环境DNA（eDNA）元条形码技术研究了日本北海道神川平原上淡水鱼群落（包括鲑鱼）的物种组成和季节性变化。我们在12个月内（2018年10月至2019年8月）在16个地点采集的176个样本中检测到23种鱼类。在每个地点检测到11至20种，包括5种天然鲑鱼（Oncorhynchus masou，Oncorhynchus keta，Parahucho perryi，Salvelinus leucomaenis leucomaenis和Salvelinus malma krascheninnikova）。在所有16个地点都检测到了入侵的外星虹鳟Oncorhynchus mykiss，它是最常见的鲑鱼。尽管在研究区域中我们没有发现虹鳟明显竞争性地排斥鲑鱼，但入侵物种的发生频率和位置都比任何其他物种都要多。我们还确定了鱼类群落的发生情况和季节变化，分类为本地鲑鱼，入侵性虹鳟鱼，鲤形目和其他底栖鱼类。冬季总体物种较少，但冬季物种丰富度较高的地区在河的下游。此外，尽管它们不如虹鳟鱼流行，但我们发现了诸如金枪鱼，假单孢菌等家庭入侵者。这些结果证明了eDNA元条形码的有效性，可用于在生态系统规模上调查物种丰富度。特别是，可以通过eDNA监测来检测入侵物种的建立和传播的早期阶段。