We describe a new species of cave-dwelling loach, Triplophysa wulongensissp. nov., based on specimens collected in a subterranean pool in a cave in Wulong County, Chongqing, Southwest China. The pool is connected to the Wujiang River drainage. Triplophysa wulongensis differs from its congeners by the following combination of characters: eyes present, caudal fin with 18 branched rays; posterior chamber of the air bladder degenerate; stomach U-shaped; intestine without bends or loops immediately posterior to stomach; body smooth and scaleless, and lateral line complete. The mitochondrial cytochrome b sequence differs from those of other published sequences of species of Triplophysa by 14.9–24.9% in K2P distance. Phylogenetic analysis based on cytochrome b gene sequences recovered T. wulongensis as sister taxon to all other cave-dwelling species of Triplophysa.

Environmental DNA (eDNA) is a good indicator of fish diversity and distribution in aquatic environments. This study used metabarcoding to assess fish diversity and distribution in two connected ponds during two sampling periods. The eDNA analysis of surface samples displayed differences in the fish communities between the two connected ponds, while within each sampling site the species detected across the two time points were not always the same. These results revealed poor horizontal transport of eDNA between the two connected ponds alongside poor mixing of eDNA for a single pond’s stocked fish. Additionally, water temperature, pH, and total nitrogen were the key environmental factors affecting fish eDNA spatial and temporal distribution. These findings have important implications for designing eDNA sampling strategies in lentic ecosystems; for example, complete fish diversity in a lentic ecosystem cannot be detected by collecting only surface samples and in only one sampling period.

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