Revisiting the Conservation Status of Cobitis taenia in Switzerland Using Environmental DNA

ABSTRACT Freshwater loaches of the genus Cobitis are small benthic fish inhabiting fine sediments in slow‐flowing rivers and vegetated lakes. Due to their small size, low economic value and inconspicuous behaviour, they are rarely studied, and their taxonomy and distribution remain poorly understood. In Switzerland, two species are considered native: Cobitis taenia north of the Alps and Cobitis bilineata in the southern Po basin. Historically, all loaches north of the Alps were attributed to C. taenia , and those to the south to C. bilineata . However, due to their morphological similarity, misidentifications have been common, and the true distribution of each species remains uncertain. Recent studies using morphological and environmental DNA (eDNA) methods have detected only C. bilineata north of the Alps, suggesting that C. taenia may never have been present in this region or has since disappeared. However, the existence of relict populations cannot be entirely ruled out. In this study, 35 rivers in western Switzerland (cantons of Vaud, Fribourg, Geneva and Neuchâtel) were surveyed using high‐volume eDNA filtration (up to 60 L per sample). C. bilineata was detected in 10 of the 35 watercourses—2 in the Rhône basin and 8 in the Rhine basin—whereas no C. taenia was found. These results support the hypothesis that C. taenia is absent or extinct in western Switzerland. A parallel museum survey also confirmed that specimens collected as early as 1962 could be attributed to C. bilineata on the basis of morphology. This study confirms the effectiveness of high‐volume eDNA sampling in detecting cryptic species such as C. bilineata .