Tarim schizothoracin (Schizothorax biddulphi) is an endemic fish species native to the Tarim River system of Xinjiang and has been classified as an extremely endangered freshwater fish species in China. Here, we used a next generation sequencing platform (ion torrent PGM™) to obtain a large number of microsatellites for S. biddulphi, for the first time. A total of 40577 contigs were assembled, which contained 1379 SSRs. In these SSRs, the number of dinucleotide repeats were the most frequent (77.08%) and AC repeats were the most frequently occurring microsatellite, followed by AG, AAT and AT. Fifty loci were randomly selected for primer development; of these, 38 loci were successfully amplified and 29 loci were polymorphic across panels of 30 individuals. The H_o ranged from 0.15 to 0.83, and H_e ranged from 0.15 to 0.85, with 3.5 alleles per locus on average. Cross-species utility indicated that 20 of these markers were successfully amplified in a related, also an endangered fish species, S. irregularis. This study suggests that PGM™ sequencing is a rapid and cost-effective tool for developing microsatellite markers for non-model species and the developed microsatellite markers in this study would be useful in Schizothorax genetic analysis.

To protect the germplasm resources of Schizothorax biddulphi, we developed and used 20 pairs of polymorphic microsatellite primers to analyze the genetic diversity and structure of populations. A total of 126 samples were collected from the Qarqan River (CEC), Kizil River (KZL), and Aksu River (AKS) in Xinjiang, China. The results showed that 380 alleles were detected in 20 pairs of primers and the average number of alleles was 19.0. The effective allele numbers and Nei’s gene diversity ranged from 1.1499 to 1.1630 and 0.0962 to 0.1136, respectively. The Shannon index range suggested low levels of genetic diversity in all populations. The genetic distance between the CEC and AKS populations was the largest, and the genetic similarity was the smallest. There was a significant genetic differentiation between CEC and the other two populations. The UPGMA clustering tree was constructed based on population genetic distance, and the clustering tree constructed by individuals showed that the AKS population and KZL population were clustered together, and the CEC population was clustered separately. Also, the group structure analysis also got the same result. It can be seen that although the three populations of S. biddulphi do not have high genetic diversity, the differentiation between the populations was high and the gene flow was limited, especially the differentiation between the CEC population and the other two populations. This study not only provided genetic markers for the research of S. biddulphi but the results of this study also suggested the need for enhanced management of S. biddulphi populations.

The Kizil reservoir in the Tarim River basin is an important habitat for the native Schizothoracinae fish (including Aspiorhynchus laticeps, Schizothorax biddulphi, Schizothorax eurystomus, Schizothorax intermedius and Schizothorax barbatus). Unfortunately, these species are threatened by many exotic fish, such as Ctenopharyngodon idellus, Silurus asotus. As an isolated habitat, the Kizil reservoir is an ideal area for studying biological invasions. However, the impact of invasive species on indigenous species in this reservoir remains unknown. In this study, the niche width and niche overlap between invasive and indigenous species in Kizil reservoir were studied based on stable isotope analysis. The results showed that niche width of two invasive species, S. asotus and C. idellus, was larger than that of native fish species, which confirmed the hypotheses that successful invaders have larger niche width. The niche overlap analysis showed that the two invasive species had high niche overlap with native fish species, which meant that there might be intensive interspecific competitions between them. The invasion of non-native species could be the main reason for the decrease of native species in the Kizil reservoir.

The escalating scarcity of freshwater resources necessitates the utilization of alternative saline waters for sustainable aquaculture. Perca schrenkii, an endemic fish from the Ili River basin, demonstrates considerable potential for cultivation in chloride-type saline–alkaline waters: its 96 h acute salinity tolerance is higher than that of freshwater populations of its congeneric Perca fluviatilis. This study systematically investigated the histomorphological responses of its key osmoregulatory and metabolic organs—gill, kidney, intestine, and liver—under acute (12–14 ppt for 96 h) and chronic (3–7 ppt for 60 days) salinity stress. Acute exposure induced dose- and time-dependent structural damage, including lamellar fusion in gills, glomerular reduction in kidneys, mucosal atrophy in intestines, and hepatocellular swelling. In contrast, chronic acclimation revealed active remodeling, such as lamellar shortening, renal tubular dilation, intestinal muscularis thickening, and biphasic hepatocyte adjustments. A hierarchical framework of structural adaptation was proposed, delineating Safe (≤3 ppt), Acclimation (5 ppt), Tolerance (7 ppt), and Lethal (≥13 ppt) zones. These findings elucidate the structural basis of salinity tolerance in Perca schrenkii and provide practical morphological indicators for assessing fish health in saline aquaculture.

This study focused on T. strauchii in Sayram Lake, Xinjiang. In August 2023, a total of 768 samples were collected to investigate its morphological, age, and growth characteristics. T. strauchii has an elongated body with a slightly raised area behind the head. Its head is flat, the body is slender, the back contour is arc-shaped, the trunk is thick and round, and the tail is short. Principal component analysis (PCA) showed that the cumulative contribution rate of the first three principal components was 53.80%, which reflects the morphological characteristics of the species. Moreover, gender characteristics are not prominently manifested in external morphology. Discriminant analysis showed an accuracy rate of 51.80%, indicating that the accuracy of gender discrimination relying solely on external morphology is limited. The species’ age distribution ranges between 1 and 7 years old, with the dominant age around 3 years old, and age structure showing a unimodal distribution. The relationship between body length and body weight is W = 7.432 × 10⁻⁶L^3.037(R² = 0.995, n = 768). The exponent 3.037 indicates a growth pattern with priority given to body mass growth because it is greater than 3. The von Bertalanffy growth equation was selected to describe the growth of T. strauchii. The body length growth equation is L_t =139.346 [1 − e^{−0.267(t+1.639)}], and the body mass growth equation is W_t = 27.79 [1 − e^{−0.267(t+1.639)}]^3.073. The inflection point age (t_i) is 2.563, the growth coefficient (k) is 0.267, and the growth characteristic index(φ) is 3.715. The growth rate decreases with age, and the growth inflection point ages of males and females differ. The research findings provide basic data for population assessment, resource protection, and rational fishing in fishery resource management. This highlights the ecological adaptability of T. strauchii and emphasizes the importance of comprehensively considering multiple factors in fishery management.

Schizothorax biddulphi is an endemic fish distributed only in southern Xinjiang, China. Due to overfishing, water conservancy facilities, and other factors, as well as inherent biological limitations, resource recovery is quite difficult. For endangered fish with slow growth, late sexual maturity, and insufficient natural population supplementation, large-scale artificial reproduction and breeding are important for restoring resources. Therefore, it is urgent to optimize the reproductive regulation methods of the fish. The kiss1 gene is a key regulator of the reproductive regulation cascade, and identifying and analyzing the role of kiss1 are important for further elucidating the reproductive mechanism of S. biddulphi. To understand the characteristics of the kiss1 of S. biddulphi, the full-length cDNA sequence of kiss1 was obtained in this study, and its tissue expression specificity and association with phenotypic traits were analyzed in male fish. The full-length cDNA sequence of kiss1 in S. biddulphi was 658 bp, with an ORF of 327 bp, and encoded a 108-amino acid, unstable protein. Homology results indicated that kiss1 was highly conserved. qPCR showed kiss1 expression in different tissues in male S. biddulphi, with the highest expression in the gonads, followed by muscle, and significantly lower expression in the swim bladder, pituitary gland, heart, hypothalamus, gill, fin, liver, eye, and mid-kidney. qPCR revealed three SNP loci in the exonic region of kiss1. The c.3G>T locus was significantly correlated (p < 0.05) with gonad mass and the maturation coefficient in S. biddulphi. These results will help uncover the reproductive endocrinology network of S. biddulphi, improve artificial breeding technology for fish, and unveil new directions for breeding excellent strains of S. biddulphi and molecular marker-assisted breeding.