Phylogenetic Relationships of Troglonectes (Cypriniformes, Nemacheilidae), with Description of Two New Species

Troglonectes is an endemic cavefish genus of Nemacheilidae, mainly distributed in Guangxi and Guizhou, China. In April 2025, ten specimens of Troglonectes were collected from a subterranean stream of a Liujiang River tributary in Jinchengjiang District, Hechi City, Guangxi. Based on morphological comparisons and molecular phylogenetic analyses using mitochondrial Cyt b and COI genes, these specimens were identified as two new species, namely Troglonectes bottazzii sp. nov. and Troglonectes chenlixini sp. nov. Troglonectes bottazzii sp. nov. can be distinguished from congeners by having scales posterior to the dorsal fin origin, 9–10 branched dorsal fin rays, 12–13 branched pectoral fin rays, and 14 branched caudal fin rays. Troglonectes chenlixini sp. nov. is characterized by 12 branched caudal fin rays. Phylogenetically, the two new species form reciprocally monophyletic lineages with strong support, and their genetic distances meet the interspecific divergence level of Nemacheilidae. The two new species live in sympatry in the same cave waterbody, which is rare among cave loaches. Their stable morphological differences imply niche differentiation in their microhabitat and feeding ecology, which may reduce interspecific competition and likely contributes to reproductive isolation. This discovery enriches the diversity of Troglonectes and represents a valuable case and promising system for future investigations of sympatric distribution and adaptive evolution of cave-dwelling fishes.