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Natural hybridization plays an important role in species evolution, and its heterosis also provides inspiration for breeding. The present study is to compare the genetic diversity and muscle nutritional quality of Schizothorax waltoni , Schizothorax o’connori , and their natural hybrids that are naturally distributed in the Yarlung Zangbo River. Based on the cluster analysis, the genetic relationship between 13 hybrids (namely S. w. ♀ hybrid) and S. waltoni was found to be closely related, whereas 24 hybrids (namely S. o. ♀ hybrid) were closely related to S. o’connori . The haplotype polymorphisms across the four populations varied between 0.847 and 0.936, while the nucleotide polymorphisms were 0.00305–0.00418. The genetic diversity of the two hybrids was higher than that of S. waltoni and S. o’connori . The crude fat content of the two natural hybrids is significantly higher than that of S. waltoni and S. o’connori . The total amino acid (TAA), essential amino acid (EAA), and delicious amino acid (DAA) contents and the EAA index (EAAI) in the two hybrids were greater than those in S. waltoni and S. o’connori . Compare to S. waltoni (22) and S. o’connori (18), the two natural hybrids (both 24) showed the richer types of fatty acids. The highest contents of polyunsaturated fatty acids (PUFAs), ω ‐3 PUFAs, and ω ‐6 PUFAs were observed in S. waltoni , and ω ‐6 PUFA within the two hybrids possessed intermediate characteristics. In conclusion, the hybrids of S. waltoni and S. o’connori showed advantages of growth rate, genetic diversity, and nutrition quality, therefore appearing to have a potential of breeding for further development and utilization.

The morphological variation in Schizothorax oconnori, Schizothorax waltoni, and their natural hybrids was examined using conventional and image‐based analysis approaches. In total, 38 specimens of S. oconnori, 35 of S. waltoni, and 37 natural hybrids were collected from the Shigatse to the Lhasa section of the Yarlung Zangbo River during June and July 2021. A total of 21 morphometric, 4 meristic, and 27 truss variables were employed for the classification of S. oconnori, S. waltoni, and natural hybrids. Principal component analysis (PCA) and factor analysis (FA), as well as discriminant function analysis (DFA) and cluster analysis (CA), were conducted to identify differences based on traditional and truss measurements. Four principal components explained 75.92% of the variation among the morphometric characters, while five principal components accounted for 79.69% of the variation among the truss distances. FA results showed that factor 1 was associated with head shape, and factor 2 was associated with fins based on morphometric characters. Among the truss characters, factor 1 was related to head shape, and factor 2 was related to chest shape. In DFA, morphometric measurements achieved higher accuracy (100%) compared to truss distances (94.55%). The head morphology of hybrids exhibited intermediate traits between S. oconnori and S. waltoni. Both morphometry‐based and truss‐based clustering indicated that the morphology of natural hybrids leaned toward S. oconnori. In conclusion, the combination of morphometric and truss analysis is beneficial for classifying S. oconnori, S. waltoni, and their natural hybrids. The presence of natural hybrids could be considered an evolutionary response to the differentiation of nutritional and spatial niches in the middle Yarlung Zangbo River. The combination of morphometric and truss analysis is beneficial for classifying Schizothorax oconnori, Schizothorax waltoni, and their natural hybrids. The presence of natural hybrids could be considered an evolutionary response to the differentiation of nutritional and spatial niches in the middle Yarlung Zangbo River.

Schizothorax waltoni has garnered significant interest due to its ecological and evolutionary significance. Despite its pivotal role in estrogen biosynthesis and sex differentiation, the Cyp19a gene has been underexplored in this species. This study showed that the SwCyp19a gene's full-length open reading frame was found to consist of 1554 nucleotides, encoding a protein with 517 amino acid residues. Phylogenetic analysis indicated high sequence identity with Cyp19a genes from other fish species, positioning SwCyp19a within a closely related clade. Tissue distribution analysis revealed predominant expression of Cyp19a in the ovaries, with sexually dimorphic expression patterns showing higher levels in females compared to males. Sexual dimorphic expression patterns refer to the phenomenon where the expression of certain genes or proteins varies significantly between males and females. This study provides the first comprehensive characterization of the Cyp19a gene in S. waltoni, highlighting its sexually dimorphic expression and potential role in sex differentiation. These findings contribute to the broader understanding of reproductive biology in high-altitude fish species and offer valuable insights for future conservation and genetic studies, and consider linking this to practical applications for fish conservation efforts.

In this paper, based on the improved DeepSORT algorithm, four target species of passing fish ( Schizothorax o’connori , Schizothorax waltoni , Oxygymnocypris stewartii and Schizopygopsis younghusbandi ) from a fishway project in the middle reaches of the Y River were used to achieve dynamic identification and automatic counting of passing fish species using fishways monitoring video. This method used the YOLOv5 model as the target detection model. In view of the large deformation by fish body twisting, the network structure of the re-identification (ReID) model was deepened to strengthen the feature extraction ability of the model. It was proposed to identify and track fish that cross the line by setting a virtual baseline to achieve the dynamic identification of fish species passing and the automatic counting of upward and downward quantities. The results showed that 1) among the five models, YOLOv5n, YOLOv5s, YOLOv5m, YOLOv5l, and YOLOv5x, the highest value of mean average precision (mAP) was 92.8% achieved by the YOLOv5x model. Specifically, recognition accuracies of 96.95%, 94.95%, 88.79%, and 91.93% were recorded for Schizothorax o’connori , S. waltoni , S. younghusbandi and O. stewartii , respectively. 2) The error rate of the improved ReID model was 20.3%, which was 20% lower than that before the improvement, making it easier for the model to obtain target features. 3) The average accuracy of the improved DeepSORT algorithm for counting four target fishes was 75.5%, among which the accuracy of Schizothorax o’connori , S. waltoni , S. younghusbandi and O. stewartii were 83.6%, 71.1%, 68.1%, and 79.3%, respectively. Meanwhile, the running speed was 44.6 fps, which met the real-time monitoring. This method is the first to implement intelligent identification of the target passing fish in fishways projects, which can accumulate long series monitoring data for fishways operation and management and provide a technical solution and reference for the work related to the realization of intelligent and informative passing fish monitoring.

Due to a sharp decline in resources, Schizothorax waltoni Regan and Percocypris retrodorslis have been listed as wildlife under second-class protection in China. Under culture conditions, the early development and allometric growth patterns of S. waltoni and P. retrodorslis were researched from the hatching stage to 60 DPHs (days post-hatching), and a sampling of ten to fifteen larvae was made every day, followed by measurements with Axio Vision 4.8 software (Carl Zeiss AG, Jena, Germany). Morphological indicators included the anal fin length, the body depth, the body depth at the anus level, the caudal fin length, the dorsal fin length, the eye diameter, the head length, the head depth, the pectoral fin length, the tail length, the trunk length, the snout length, the total length, and the ventral fin length. Based on the morphology development of S. waltoni Regan and P. retrodorslis, four periods of larval growth were identified: pre-flexion larvae at 0–14 DPHs and 0–16 DPHs; flexion larvae at 14–23 DPHs and 16–26 DPHs, post-flexion larvae at 23–50 DPHs and 26–52 DPHs, and the juvenile stage. In newly hatched larvae, most organs and body parts were not differentiated, and they successively developed within 26 DPHs. The depletion of the yolk sac was observed at 23 DPHs and 25 DPHs. Allometric growth mainly occurs in the head and tail regions, indicating that body parts related to feeding and swimming behaviors were more important than the other parts. In addition, the growth pattern shows that the development of organs gives priority to the functions of gill respiration, sensation, exogenous feeding, and swimming. The inflection points of body part growth patterns only appeared before 40 DAH, so future studies should concentrate focus on developing the best feeding from the first feeding to 40 DAH. These outcomes were discussed with regard to the ontogeny of the functional morphology in relation to ecology and aquaculture. It is expected that this research can provide valuable perspectives in species conservation.

The phylogeography of Schizothorax waltoni , an endemic and endangered tetraploid schizothoracine fish in the Yarlung Tsangpo River (YLTR) on southern margin of Qinghai-Tibet Plateau (QTP), was investigated using two mitochondrial DNA regions and eleven microsatellite loci. Analyses of concatenated sequences of cytochrome b (1141 bp) and the control region (712 bp) revealed high haplotype diversity and moderate nucleotide diversity. High genetic diversity was observed based on microsatellite variation. Both mtDNA and microsatellite analyses revealed significant genetic differentiation between the eastern population (Mainling) and the other four populations to the west, and non-significant genetic differentiation amongst the three central populations in the west. Significant genetic differentiation was observed between the western population (Shigatse) and the three central populations based on microsatellite analyses alone. Bayesian skyline plot analyses showed that S. waltoni experienced a pronounced population expansion 0.05 to 0.10 Ma. Hierarchical structure analyses of microsatellite data indicated that S. waltoni could be split into three groups (western, central and eastern YLTR). The results indicate that three management units should be considered for S. waltoni . Our findings highlight the need for the conservation and effective management of S. waltoni , which is a key member of the endemic and highly threatened fishes of the QTP.

The reproductive biology of Schizothorax waltoni (Cyprinidae: Schizothoracinae) was studied by examining 1,145 individuals collected between August 2008 and August 2009 in the Yarlung Zangbo River, Tibet. The population had a significantly higher proportion of females than males (χ2 test, p < 0.05). Using a logistic regression, it was determined that the standard lengths at 50 % maturity were 369 mm for males and 479 mm for females; the ages at 50 % maturity were 10.2 years for males and 13.5 years for females. Based on the monthly proportions of macroscopic gonadal maturity stages and monthly variations in the gonadosomatic index, S. waltoni spawned over a short period, from March to April with a peak in March According to the size distribution of oocytes, S. waltoni appeared to show a high degree of spawning synchronicity. The fecundity of S. waltoni increased linearly with the standard length, body weight and ovary weight, but had no significant correlation with age. The mean fecundity of 21693 and mean relative fecundity of 13.4 eggs per gram of fish body weight suggest that S. waltoni might be especially vulnerable to exploitation.

As a vulnerable species in the Red List of China’s Vertebrates , Schizothorax waltoni ( S. waltoni ) is mainly distributed in the middle reaches of Yarlung Tsangpo River in Tibet. Due to its delicate meat and delicious taste, S. waltoni is the main economic fish in the producing area. But recently, it has undergone a drastic population decline due to the overfishing of fishery resources, the invasion of foreign species, environmental pollution and other factors. Therefore, it is extremely urgent to protect germplasm resource of S. wa ltoni. In this study, we used Illumina Hiseq 4000 sequencing to develop single nucleotide polymorphism (SNP) markers in S. waltoni. Based on a large number of transcriptome sequences and candidate SNP loci obtained by previous transcriptome studies, 63 SNPs were randomly selected from immune-related genes and 36 loci exhibited significant polymorphisms in genotyping by Sequenom MassARRAY. The observed heterozygosity and expected heterozygosity varied from 0.0789 to 0.9577 and 0.0763 to 0.5033, respectively. There is only 5 SNP loci accord with Hardy–Weinberg equilibrium ( p  > 0.05) and no linkage disequilibria. These polymorphic SNP markers could be used for conservation genetics research in S. waltoni , and may provide new insights into future conservation strategies.

To better understand the biology of Schizothorax waltoni, the age structure and growth characteristics of S. waltoni were examined. The standard length (SL) range was 41-642 mm and the body weight (BW) range was 1.1-3788.1 g. Otoliths continually grew with increasing SL and increasing age, but asymmetrically over time. One annulus was formed each year, between April and July. Estimated age range was 4-37 yr for males, 4-40 yr for females, and 1-9 yr for those of undetermined sex. The SL-BW relationship was described as BW = 1.365 × 10 −5 SL 2.984 for females, BW = 1.238 × 10 −5 SL 2.999 for males, and BW = 3.664 × 10 −5 SL 2.800 for undetermined specimens. The von Bertalanffy function was used to model the observed length-at-age data as Lt = 644.3 {1 − exp [−0.084(t − 0.247)]} for females, and Lt = 586.2 {1 − exp [−0.084(t + 2.250)]} for males. Females grew faster than males. Knowledge of this species' characteristics of slow growth and a long life will be useful for establishing reasonable management practices for its conservation.