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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.

As one of the most sensitive regions to global climate change, Tibet is subject to remarkable changes in biota over the past decades, including endemic fish species. However, no study has attempted to predict the changes in the distribution of Tibetan fishes, leaving a great blank for aquatic conservation in Tibet. Based on the Maximum Entropy model (MaxEnt), this study predicted the changes in the suitable habitats of three endemic fish species, including two species mainly inhabiting the rivers (Glyptosternon maculatum, Oxygymnocypris stewartii) and one species mainly inhabiting lakes (Gymnocypris selincuoensis) in Tibet under two representative concentration pathways (RCP2.6 and RCP8.5) under two future scenarios (2050 and 2090), and explored the impact of the barrier effects of hydropower projects on the suitable habitats of fish. The results showed that under the four scenarios, the net change in the suitable habitats of the G. maculatum was negative (−2.0–−18.8%), while the suitable habitats of the O. stewartii and G. selincuoensis would be expanded, with the net change of 60.0–238.3% and 46.4–56.9%, respectively. Under different scenarios, the suitable habitats of the three species had a tendency to migrate to a higher elevation, and the largest expansion in the range of migration was projected to occur under the 2090-RCP8.5 scenario. In addition, due to the impact of the hydropower projects, the ability of G. maculatum to obtain new suitable habitats from climate change would be reduced by 2.0–8.1%, which was less than the loss induced by climate change (5.5–25.1%), while the suitable habitats of O. stewartii would be reduced by 3.0–9.7%, which was more than the impact of climate change (about 1%). The results of this study have guiding significance for the conservation and management of fish resources diversity in the Yarlung Tsangpo River basin and Siling Co basin of Tibet, and also provide a reference for the coordination and scientific planning of hydropower projects in Tibet.

Animal genomes in the Qinghai-Tibetan Plateau provide valuable resources for scientists to understand the molecular mechanism of environmental adaptation. Tibetan fish species play essential roles in the local ecology; however, the genomic information for native fishes was still insufficient. Oxygymnocypris stewartii, belonging to Oxygymnocypris genus, Schizothoracinae subfamily, is a native fish in the Tibetan plateau living within the elevation from roughly 3,000 m to 4,200 m. In this report, PacBio and Illumina sequencing platform were used to generate ~385.3 Gb genomic sequencing data. A genome of about 1,849.2 Mb was obtained with a contig N50 length of 257.1 kb. More than 44.5% of the genome were identified as repetitive elements, and 46,400 protein-coding genes were annotated in the genome. The assembled genome can be used as a reference for future population genetic studies of O. stewartii and will improve our understanding of high altitude adaptation of fishes in the Qinghai-Tibetan Plateau.

Oxygymnocypris stewartii is a cold‐water cyprinid indigenous to China, where it inhabits the Yarlung Zangbo river and its tributaries at high elevations on the Qinghai–Tibet plateau. Owing to its restricted distribution and a gradual reduction in population size, this fish is listed as near threatened on the IUCN Red List, and it is classified as endangered at the national level. To investigate the species’ genetic diversity, this study used 26 pairs of microsatellite markers to analyse the genetic structure of six geographic populations of O. stewartii in the Yarlung Zangbo river basin (YZRB). The results showed moderate genetic diversity in O. stewartii, with an average effective number of alleles of 2.4052, expected heterozygosity of 0.4759, and polymorphism information content of 0.4210. Genetic structure analysis detected significant differentiation among the six populations (p < 0.05). Bayesian inference of ancestral lineage indicated the populations comprise two genetically distinct groups. Small effective population sizes are possibly an outcome of a reduction in the whole population and obstacles to gene exchange among geographic populations. Analysis of gene flow found evidence of asymmetrical migration, with migration from larger to smaller populations. This research provides a genetic basis for protection of this threatened species, with O. stewartii in the YZRB deserving urgent protection. This study clarified the status of the genetic diversity and genetic structure of Oxygymnocypris stewartii in the Yarlung Zangbo river Basin using microsatellite markers. Although the results showed that the species displays moderate genetic diversity, the population had a small effective size and were significantly differentiated, and the genetic structure analysis showed that the populations consisted of two ancestral lineages, which indicated that O. stewartii merits urgent protection.

Schizothorax o’connori and Oxygymnocypris stewartii are two endangered endemic Tibetan fishes that thrive in the Lhasa River at an average altitude over 4000 m. During artificial reproduction of endemic Tibetan fishes, the juvenile fish of S. o’connori and O. stewartii experienced mass mortality event. The causative agent is diagnosed to be a ciliate parasite, Chilodonella piscicola (syn. C. cyprini), which is common in various fishes. Here, we supplemented its description based on the morphological and molecular data. The body of C. piscicola is oval, 30–60 × 25–40 μm in vivo. Cyrtos is hook-like, composed of 9–10 toothed nematodesmal rods. Somatic kineties usually contain seven right kineties and nine left kineties. Two parallel circumoral kineties revolve round the cyrtos, and one preoral kinety extends to the anterior end of the fourth left-most kinety. Terminal fragment kinety is linear and on the top left of dorsal side. Sequence alignments revealed that the present SSU rDNA and ITS1-5.8S-ITS2 sequences are both most similar to the sequences of C. uncinata with the similarities of 98.2 and 99.5 %. The phylogenetic analyses showed that C. piscicola is sister to other Chilodonella species, whereas C. cyprini (FJ873805) cluster with Tetrahymena species. Molecular analysis shows that the ITS1-5.8S-ITS2 sequence of C. cyprini in GenBank is unreliable. Our study extended the host range of C. piscicola and supplemented and revised the molecular data. Besides, as far as we know, this is the first record of C. piscicola in Tibetan plateau.

Summary Length–weight relationships and length–length were evaluated for three fish species (Schizopygopsis younghusbandi Regan, 1905; Ptychobarbus dipogon Regan, 1905 and Oxygymnocypris stewartii Lloyd, 1908) from the Yarlung Zangbo River in Tibet. Specimens were captured monthly using floating gillnets (mesh size 7.5 cm), bottom gillnets (mesh size 6.5 cm), and trap nets (mesh size 1.5 mm) from August 2008 to August 2009, March to August 2012, and March to April 2013. Regression coefficient (b) values of length–weight relationships (LWRs) ranged from 3.045 for P. dipogon to 3.193 for O. stewartii, whereas the a values ranged from 0.0040 to 0.0168 for O. stewartii and P. dipogon, respectively.

The complete mitochondrial genome of the hybrid of O. stewartii (female) and S. younghusbandi (male) was sequenced and characterized in this study. The complete hybrid mitochondrial genome is 16,649 bp in length, including 2 rRNAs, 13 protein-coding genes, 22 tRNAs and 2 non-coding regions (OL and D-loop region). The results discovered that 99.89% sequence identity between the hybrid and its female parent, which confirmed the maternal inheritance pattern followed by the mitochondrial genome of the hybrid. The phylogenetic tree showed that the hybrid was relatively closer to O. stewartii. Our data would provide a valuable resource for further studies on mitochondrial inheritance mechanism of Schizothoracinae fishes and provide new insights for better conservation plans for fishery resources.

Summary A 95‐day experiment was conducted to evaluate the performance of a visible implant elastomer tag (VIE) versus a coded wire tag (CWT) implanted in juvenile Tibet fish Oxygymnocypris stewartii (Lloyd, 1908; total length 5~7 cm) under laboratory conditions. Mortality, tag retention and growth in three groups of juvenile O. stewartii (VIE‐tagged, CWT‐tagged and control) in duplicate were determined in six indoor tanks (300‐L/tank volume, 100 fish/tank) at 15.6 ± 0.5°C water temperature. Results showed that neither tagging method had a significant difference on the mortality of the experimental fish, but that the growth rate in the VIE group was significantly lower than in the CWT and control groups. Mean tag retention in the VIE group was 95.2%, and 98.9% in the CWT group, with no significant differences in tag retention in the two methods. The study indicates that both VIE and CWT are suitable short‐term tagging methods for hatchery O. stewartii juveniles.

This paper reports the length–weight relationships for six fish species belonging to the Cyprinidae from the middle of the Yalu Tsangpo River in China. Samples were obtained by electroshock and drift net fishing techniques (mesh size 2 cm × 3 cm; 200 m net length) in April and September to October 2014. Length–weight relationships estimates for these species were not available in FishBase. A total of 737 specimens were used to estimate the a and b parameters. New maximum total lengths are also reported for six species. The r² values range from 0.98 to 0.99. Values of b vary from 2.88 to 3.19.

Feeding habits of Oxygymnocypris stewartii were investigated based on monthly sampling in the Yarlung Zangbo River from August 2008 to August 2009. The gut contents of 194 individuals were analysed and quantified with numerical and gravimetric methods. This species can be considered a generalized and opportunistic predator feeding both on teleosts and aquatic insects. A multivariate analysis revealed noticeable variation in O. stewartii diet composition with fish size and season. The smaller specimens fed primarily on Cobitidae and Hydropsychidae. As they grew, Cyprinidae and Chironomidae larvae became important prey. The preferred food items were teleosts in summer and autumn. For winter and spring, the predominant prey switched to chironomidae larvae. Diet composition did not significantly vary between the sexes. Finally, a significant and positive correlation between predator and prey length was found. These findings provide the fundamental information better understanding the role of this important endemic species in the Yarlung Zangbo River food web.