Yang Zhou

Schizothoracinae represent an endemic and dominant teleost group in the Qinghai–Xizang Plateau and adjacent regions. Despite their rich species diversity, closely related Schizothoracinae species exhibit remarkable external morphological similarity, which hinders traditional morphological discrimination. In this study, lapillus otoliths from 360 individuals representing 12 Schizothoracinae species collected across major Tibetan water systems were systematically examined. We evaluated and compared the performance of traditional scalar-based shape indices and Elliptic Fourier Analysis (EFA, 60 normalized harmonic coefficients following size-allometry correction) in otolith contour quantification and species identification. Statistical analyses including one-way ANOVA, principal component analysis (PCA), non-linear manifold learning (t-SNE and UMAP), and linear discriminant analysis (LDA) were executed. One-way ANOVA revealed highly significant differences among all 12 species across all shape indices and Fourier coefficients. The overall LDA classification accuracy was 35.3% for the shape index method, whereas EFA achieved a higher overall accuracy of 68.3%, representing a 33.0 percentage point improvement. Under EFA, Schizothorax lhasaensis (93.3%) and Schizothorax nukiangensis (90.0%) demonstrated the highest single-species discrimination success. Interspecific otolith morphological divergence was substantially higher in the riverine genus Schizothorax than in lacustrine genera (Gymnocypris and Schizopygopsis), the latter two of which show extensive morphological overlap consistent with their low genomic differentiation. Fishes of Gymnocypris displayed significantly higher otolith roundness (p < 0.05), which correlates with their adaptation to lacustrine or sluggish water habitats. Our findings demonstrate that EFA effectively captures multi-scale otolith contour harmonics, serving as a valuable morphometric approach for Schizothoracinae species identification and morphological discrimination, although challenges remain for species with incomplete lineage sorting. The morphometric database established herein provides valuable morphological baselines for the conservation and management of endemic QXP fish resources.

The river ecosystems of the Qinghai–Tibet Plateau, recognized as a vital component of the “Asian Water Tower,” possess unique hydrological conditions and extreme environments that have shaped key indicator groups, most notably zooplankton. The community dynamics and structural characteristics of these zooplankton exhibit regular spatio-temporal distribution patterns across elevational gradients and seasonal successions. However, the intrinsic mechanisms underlying community succession and their correlations with environmental factors remain poorly understood, and the primary environmental drivers influencing community structure require further elucidation. Based on systematic zooplankton surveys and environmental data collection conducted across the Lhasa River basin from 2019 to 2021, this study established a comprehensive species inventory comprising 113 taxa across four major groups, alongside a multi-dimensional environmental dataset. We analyzed the spatio-temporal heterogeneities of zooplankton community structures—including abundance, biomass, and diversity indices—across different seasons and river reaches. The results revealed the composition and seasonal turnover of dominant taxa, with rotifers accounting for 39.82% of the total taxonomic richness. Mean zooplankton abundance and biomass across the basin were 1.18 ind./L and 343.60 × 10⁻⁵ mg/L, respectively, with peak values observed during autumn and within the Chabalang Wetland. The zooplankton community structure in the upstream, midstream, and downstream reaches, as well as associated wetlands, was significantly correlated with specific environmental factors (p < 0.05), including ammoniacal nitrogen (NH₄⁺-N), magnesium (Mg²⁺), total hardness (TH), potassium (K⁺), iron (Fe²⁺), sodium (Na⁺), sulfite (SO₃²⁻), nitrate ion (NO₃⁻), chloride ion (Cl⁻), total phosphorus (TP), and sulfide (S²⁻). Cl⁻, TH, Mg²⁺, SO₃²⁻, and elevation (Ele) were the key environmental drivers significantly influencing zooplankton abundance across seasons (p < 0.05). Furthermore, zooplankton abundance decreased significantly with increasing elevation during the winter. This research deepens our understanding of community assembly mechanisms in plateau river ecosystems and provides a scientific foundation for aquatic biodiversity conservation and ecological management in the Lhasa River basin.

This research examines the otolith microchemical characteristics of the critically endangered kunming snout trout (Schizothorax grahami) collected from the sources section endemic to the Chishui River, China, a tributary of the upper Yangtze River, and the metal concentrations in the water of fish habitats. Among the analyzed elements, strontium (Sr) exhibited consistent distribution patterns across otolith rings, as observed through face-scan imagery (scanning the polished surface of the otolith cut), with a relatively low coefficient of variation. Statistical analysis using a paired two-tailed t-test revealed significant differences in Sr:Ca ratios among samples from the three river sections. Notably, magnesium (Mg) levels in the otolith core during the early life stages of the fish were notably higher compared to non-core regions. Similarly, Mg concentrations of water were elevated in the spawning grounds relative to non-spawning areas. This suggests that otolith Mg content may be influenced by the specific water conditions of the spawning grounds. Furthermore, Mg:Ca ratios in the otolith core displayed significant variation among samples from U3, L2, and other sites, implying that the fish in these samples originated from distinct spawning locations. These findings demonstrate that strontium and magnesium in otoliths can serve as effective markers for reconstructing the life history of S. grahami in the Chishui River and can contribute to the management of different fish stocks.

Otolith is one of the most commonly used tools to trace fish life history, as its formation is affected by environmental factors during growth. This study investigates the otolith micro-chemical information of Schizothorax grahami from the upper (U1, U2, U3), middle (M1, M2, M3) and lower (L1, L2, L3) reaches in the source section of Chishui River, China, as well as the metal content of the water corresponding to fish habitats. Seventeen active elements in otolith were detected, and calcium (Ca) content was the highest (175605.4*10-6 g/g). Only strontium (Sr) was regularly distributed in otolith rings by face-scan images with a relatively small coefficient of variation. A paired two t-test showed that the values of Sr: Ca were significant differences among the samples from the three reaches through otolith line scans. In the correlation test after the first-order difference processing, the change frequency of Sr: Ca values in the otolith corresponded better to the line plots and significantly differed among the three reaches, especially the samples from the U3 and L2 sites. Therefore, analyzing Sr in the otolith of S. grahami from three reaches can differentiate fish stocks and reveal their unique life histories. The magnesium (Mg) in the otolith core at the early stage of fish life was significantly higher than that of the non-core area. Likewise, Mg content was higher in the fish spawning ground than in the non-spawning ground. Presumably, Mg content in the otolith was correlated to the water environment of the spawning ground. Meanwhile, the values of Mg: Ca in the otolith core showed significant differences among the samples from U3, L2 and the other sites, indicating that fish in these samples came from different spawning grounds. The characteristics of Mg in the otolith can reflect the life history of S. grahami in the Chishui River and the location of spawning grounds. This study indicates that strontium and magnesium in otolith can be used to trace the life history of S. grahami in the Chishui River and aid fishery management for different fish stocks.

Otoliths grow throughout a fish’s life and are important for identifying fish stocks and fish age. This study aims to differentiate different stocks of Schizothorax grahami (Regan, 1904) in the Chishui River, an upper reach of the Yangtze River, by otolith morphology. The otolith morphology of S. grahami from three different river sections was analyzed using the Shape Index, Fourier coefficients, and wavelet coefficients. The composite discrimination success rate of the Shape Index was 59.7%, and it was difficult to distinguish in the scatter plots. In contrast, canonical principal coordinate scatter plots clearly showed three distinguished stocks. The above results indicate that otolith morphology can discriminate between stocks in plateau endemic fish, and several S. grahami stocks may be separately managed in the Chishui River.