The Tumen River, which delineates the border between China, North Korea, and Russia, is a vital river in Northeast Asia. Understanding its current fish diversity holds significant scientific value for aquatic ecological protection. Therefore, traditional and eDNA sampling were conducted from 2022 to 2023. Integrating the historical literature with our field collection results reveals that the Tumen River has a total of 64 native fish species, of which 51 species have been surveyed in the wild. The fish composition is mainly dominated by cold-water species, with a high proportion of these being rare, endangered, and nationally protected. eDNA surveys are crucial complements in boundary rivers where traditional methods are not feasible. The results indicated that α diversity values were highest in the Hunchunhe River, attributed to the favorable natural geographical conditions and effective conservation efforts. Recently, the fish diversity in the Tumen River has been disrupted, primarily reflected in the absence of migratory species such as Oncorhynchus gorbuscha and Pseudaspius hakonensis. The study suggests that establishing nature reserves, preventing and controlling alien species, and strengthening international cooperation are key to protect fish diversity.

The genus Abbottina Jordan & Fowler, 1903 comprises small benthic gobionid fishes widely distributed in East Asia. However, due to the unclear generic characteristics as defined in the original description, the taxonomic status of the species within this genus remains controversial, and its definition needs clarification. This study examined the morphology of the type species, Abbottina rivularis (Basilewsky, 1855), to more accurately redefine generic characteristics. The genus Abbottina can be distinguished from all other gobionid genera by the following characteristics: mouth inferior; lips thick, relatively smooth, with small less-developed papillae or shallow grooves; lower lip with anterior fold, medial pad forming two oval protuberances; jaws covered by lips, without horny margin; barbel one pair; the last unbranched dorsal-fin ray thin and soft; with five branched anal-fin rays; pharyngeal teeth in one row; air-bladder moderately large, possessing two soft chambers; anterior chamber enclosed in membrane capsule. Based on morphological characters and phylogeny of mitochondrial genome sequences, Abbottina lalinensis has been reassigned to the genus Microphysogobio . Further, based on the morphology of Abbottina binhi from Cao Bàng Province, this species is reassigned to the genus Oriengobio . Thus, the genus Abbottina becomes a monotypic genus.