Abstract: The cyprinid genus Sinocyclocheilus, endemic to the karst regions of southwestern China, represents the world's most species-rich cavefish radiation. Its remarkable species diversity and ecological divergence provide an ideal model for studying extreme environmental adaptation and polyploid evolution. Compared to the classic diploid cavefish model Astyanax mexicanus, Sinocyclocheilus exhibits a unique phylogenetic background, an allotetraploid origin, and distinct phenotypic evolutionary trajectories. In this review, we outline its taxonomy and phylogeny and summarize the continuous ecological morphs from surface to obligate cave dwellers alongside their phenotypic variations. We highlight the molecular mechanisms underlying key adaptive traits—including eye degeneration, pigmentation loss, scale reduction, and sensory compensation—and discuss the role of polyploidization in gene redundancy, expression regulation, and adaptive evolution. Current evidence reveals that cave adaptation in Sinocyclocheilus involves convergence through multiple evolutionary routes and synergistic trait trade-offs, which are largely facilitated by its polyploid genomic background. This review deepens our understanding of cavefish adaptation and polyploid evolution, highlighting the potential of this genus in providing valuable evolutionary perspectives and natural mutation pedigrees for deciphering fundamental biological processes.

Key words: Sinocyclocheilus, cavefish, whole-genome duplication, extreme environment adaptation, model organism