Two new cavefish species of Triplophysa (Cypriniformes: Nemacheilidae) from the karst subterranean rivers of Yunnan, China

Cavefish are of considerable interest owing to the remarkable adaptations for surviving in harsh subterranean conditions. These adaptations, often described as constructive traits or regressive features, reflect trade-offs in metabolic requirements and energy utilization in response to life in darkness. In this study, we describe two new cavefish species, Triplophysa yangi sp. nov. and Triplophysa wenshanensis sp. nov., from karst subterranean rivers in Yunnan Province, China. Triplophysa yangi is distinguished from its congeners by its bilaterally expanded anterior swim bladder chambers, which protrude from the enlarged bony capsule, distending the lateral body wall and becoming externally visible. Additionally, it has highly developed pectoral and pelvic fins with filamentous extensions. Triplophysa wenshanensis can be identified by its nearly cone-shaped head, triangular head profile, and light brown to flesh pink body colour with faint brown blotches. Molecular phylogenetic analysis places both species in the hypogean group of Triplophysa, increasing the number of cavefish species in this genus from 39 to 41. The most distinctive feature of T. yangi, its expanded anterior swim bladder chambers protruding beyond the enlarged bony capsules, might represent an innovative stygomorphic trait among Chinese cavefish. This trait is hypothesized to be associated with a unique energy-saving buoyancy mechanism, crucial for the ability of the species to remain suspended and survive in perpetual darkness.