Identification of Schizothorax species in Yarkand River, (Xinjiang, China) based on otolith morphology

This study explored the morphological characteristics and differences of the otoliths in three native species, Schizothorax biddulphi, S. eurystomus and S. curvifrons, in the Yarkand River of the Tarim River, Xinjiang, China. A total of 93 specimens (27 S. biddulphi, 39 S. eurystomus, and 27 S. curvifrons) were analyzed using six basic otolith morphological parameters (OA, Rmax, Rmin, OP, OL, OW) to derive six factors (F1, F2, F3, F4, F5, F6) and seven indices (RO, FF, CI, RE, EL, RR, AR) for morphological assessment. A discriminant analysis incorporating 77 Fourier coefficients of the otoliths revealed distinct morphological differences among the species. A significant power function relationship between otolith morphology and standard length was observed across the species, with R2 values ranging from 0.409 to 0.749. Principal component analysis (PCA) of 7 traditional otolith morphological indicators explained 81.243% of the variance, yielding an overall species discrimination rate of 81.65%. Further PCA of 77 Fourier harmonic values enhanced the discrimination accuracy, with the first 3 components accounting for 77.49% of the total variation and an improved discrimination rate of 100.00%. Cluster analysis resulted in the grouping of S. biddulphi and S. curvifrons together and revealed their association with S. eurystomus, indicating notable morphological distinctions. Both otolith shape indices and elliptical Fourier analysis have been useful in distinguishing the phenotypic units of different fish species. In this study, otolith morphology was applied for the first time to identify Schizothorax species, providing an in-depth description of species distribution and evolutionary history. This study provides a reference for the identification and systematic classification of Schizothorax species and a scientific basis for formulating effective species protection measures, for promoting the sustainable management of species and important habitats.