Sperm cryopreservation is helpful for maintaining the genetic diversity of fish species. This study was aimed at developing efficient methods to cryopreserve the sperm of three fish species, including koi carp (Cyprinus carpio L.), Ya fish (Schizothorax prenanti), and Glyptosternum maculatum. Firstly, based on the analysis of sperm viability, the cryomedium, dilution ratio, volume, and cooling procedure were assessed and optimized in koi carp. The results showed that the highest sperm viability was up to 63.23 ± 1.36% after a 14-day cryopreservation using the optimal method, briefly, sperm frozen with a volume of 50 μL (Vol.sperm:Vol.cryomedium = 1:9) of cryomedium containing 10% DMSO and 3% sucrose in D17 through ultrarapid cooling. Secondly, both the mitochondrial membrane potential and the DNA fragmentation index of sperm were examined and found to be significantly damaged after the cryopreservation. Intriguingly, the fertilization rate of sperm after 14-day cryopreservation is up to 63.03 ± 1.36% and the elongation of cryopreservation time (210 days) just slightly affected the fertilization rate (55.09 ± 4.70%) in koi carp. Thirdly, the optimal cryopreservation method was applied to cryopreserve Glyptosternum maculatum sperm; the cell viability was 45.39 ± 4.70%. And then this method, after a minor modification (3% sucrose of cryomedium replaced with 3% SMP) was adopted to cryopreserve Ya fish sperm, the cell viability was up to 70.45 ± 2.23%. Lastly, the ultrastructure and morphology of sperm was observed by SEM, and it was found that the cryopreservation prominently caused sperm head swelling and tail shortening in three fish species. In conclusion, this study established effective methods for cryopreserving sperm in three fish species and elaborated the injuries on sperm caused by cryopreservation. And the findings facilitate developing more protocols with practical value to cryopreserve sperm in different fish species.

The gut microbiota plays a pivotal role in upholding intestinal health, fostering intestinal development, fortifying organisms against pathogen intrusion, regulating nutrient absorption, and managing the body’s lipid metabolism. However, the influence of different cultivation modes on the growth indices and intestinal microbes of Salmo trutta fario remains underexplored. In this study, we employed high-throughput sequencing and bioinformatics techniques to scrutinize the intestinal microbiota in three farming modes: traditional pond aquaculture (TPA), recirculating aquaculture (RA), and flow-through aquaculture (FTA). We aimed to assess the impact of different farming methods on the water environment and Salmo trutta fario’s growth performance. Our findings revealed that the final weight and weight gain rate in the FTA model surpassed those in the other two. Substantial disparities were observed in the composition, relative abundance, and diversity of Salmo trutta fario gut microbiota under different aquaculture modes. Notably, the dominant genera of Salmo trutta fario gut microbiota varied across farming modes: for instance, in the FTA model, the most prevalent genera were SC-I-84 (7.34%), Subgroup_6 (9.93%), and UTCFX1 (6.71%), while, under RA farming, they were Bacteroidetes_vadinHA17 (10.61%), MBNT15 (7.09%), and Anaeromyxoactor (6.62%). In the TPA model, dominant genera in the gut microbiota included Anaeromyxobacter (8.72%), Bacteroidetes_vadinHA17 (8.30%), and Geobacter (12.54%). From a comparative standpoint, the genus-level composition of the gut microbiota in the RA and TPA models exhibited relative similarity. The gut microbiota in the FTA model showcased the most intricate functional diversity, while TPA farming displayed a more intricate interaction pattern with the gut microbiota. Transparency, pH, dissolved oxygen, conductivity, total dissolved solids, and temperature emerged as pivotal factors influencing Salmo trutta fario gut microbiota under diverse farming conditions. These research findings offer valuable scientific insights for fostering healthy aquaculture practices and disease prevention and control measures for Salmo trutta fario, holding substantial significance for the sustainable development of the cold-water fish industry in the Qinghai–Tibet Plateau.

This paper applies the von Bertalanffy growth equation to study the age structure and growth characteristics of 210 Ptychobarbus dipogon collected in September 2019 in the middle and upper reaches of the Yarlung Zangbo River and employs FISAT II software to estimate the population characteristics’ parameters. Its aim is to provide a basis for the conservation of the population resources of the Ptychobarbus dipogon. In this study, the length of the catch ranged from 137 mm to 475 mm, the weight ranged from 44.04 g to 1142.80 g, the minimum age was 5 years, and the maximum age was 47 years. The body length–weight relationship was W_(♀) = 4.1738 × 10⁻⁵L^2.7687 (n = 86, R² = 0.901); W_(♂) = 2.7784 × 10⁻⁵L^2.8434 (n = 100, R² = 0.918). The growth equation was Lt_(♀) = 505.000[1 − e^{−0.048(t−1.992)}]; Lt_(♂) = 452.254[1 − e^{−0.069(t−4.233)}]; Wt_(♀) = 1296.576[1 − e^{−0.048(t−1.992)}]^2.7687; Wt_(♂) = 1001.872[1 − e^{−0.069(t−4.233)}]^2.8434. The inflection point ages of the female and male Ptychobarbus dipogon were 7.95 and 6.05, respectively. The exploitation rate of Ptychobarbus dipogon was 0.61, which exceeds the optimum exploitation rate of resources (0.57). The population resources are overfished. It is suggested to strengthen the conservation of Ptychobarbus dipogon population resources and the protection of native fish on the Qinghai–Tibet Plateau.

Schizopygopsis younghusbandi is an endemic and economically important fish in the Qinghai-Xizang Plateau, but its aquaculture is limited by harsh environmental conditions and incomplete understanding of host–microbiome–environment interactions. This study applied metagenomic sequencing to examine how different culture environments affect growth, water microbial communities, and gut microbiome network stability. Three-year-old juveniles (initial body weight 50.57 ± 1.88 g) were reared for 90 days in five systems: conventional pond (P), wetland (WL), concrete tank (G), river (R), and recirculating aquaculture system (RC). No significant differences in initial body weight or length were observed among groups (p > 0.05). Fish in the RC system achieved the highest final body weight, weight gain rate, and specific growth rate (p < 0.05), while survival rates were highest in the river and RC groups and lowest in ponds (p < 0.05). Microbial diversity and community composition differed significantly among culture modes, with bacterial and protozoan communities showing the strongest environmental responsiveness. Co-occurrence network analyses revealed that RC and G systems exhibited higher network complexity, density, and proportion of positive correlations, reflecting enhanced microbial interaction and ecological stability, whereas the WL system showed reduced network connectivity. Correlation analysis indicated that bacterial abundance was positively associated with total nitrogen, total phosphorus, and dissolved oxygen (p < 0.05), highlighting environmental regulation of microbial assemblages. Overall, the aquaculture environment shapes gut microbial networks, which closely relate to growth performance. Recirculating aquaculture systems can mitigate growth limitations in plateau fish by stabilizing the environment and reinforcing gut microbial communities, providing a sustainable strategy for high-altitude aquaculture development.

The high-altitude regions of the Tibet Autonomous Region possess abundant cold-water resources, with annual average water temperatures suitable for culturing triploid rainbow trout. However, environmental challenges—including low atmospheric pressure, hypoxic water conditions, and significant diurnal temperature fluctuations—necessitate precise optimization of stocking density. Inadequate densities result in suboptimal resource utilization, whereas excessive densities induce chronic stress, leading to suppressed growth, reduced survival, and intestinal microbiota dysbiosis. Currently, research on appropriate stocking densities under these specific conditions remains limited. This study investigated the effects of stocking density on growth performance, intestinal microbiota, and tissue health of triploid rainbow trout, to identify the optimal density to support sustainable aquaculture in high-altitude plateau areas. Three stocking densities were tested over a 60-day culture period in 0.25 m³ cylindrical tanks (radius 0.45 m, water depth 0.45 m, adjusted for internal volume): Low-Density (LD, 100 fish/barrel), Medium-Density (MD, 200 fish/barrel), and High-Density (HD, 300 fish/barrel). Results demonstrated that the final body weight (Wt) and specific growth rate (SGR) in the LD treatment were significantly higher than those in the HD group (Wt: P ≤ 0.009; SGR: P ≤ 0.019). Survival rate was also significantly greater in the LD treatment compared to HD (P < 0.036), with values of 84.67%, 80.83%, and 72.67% for LD, MD, and HD, respectively. Alpha diversity of both water and gut microbial communities varied with stocking density. Principal component analysis (PCA) revealed differentiated clustering of microbial communities in water and the intestine across density treatments (Water: P = 0.35; intestinal microbiota: P = 0.7). The dominant phyla in aquatic and intestinal microbiomes were Proteobacteria, Firmicutes, and Bacteroidetes. In intestinal samples, the genus Pseudomonas was significantly more abundant in the HD and MD treatments than in the LD treatment. Co-occurrence network analysis revealed a higher average degree in LD and MD treatments, suggesting enhanced stability of microbial ecosystems in both the intestine and water under these conditions. In conclusion, low and medium stocking densities are more suitable for cultivating triploid rainbow trout in high-altitude plateau environments. These findings provide a scientific basis for ecologically sound, efficient, and healthy aquaculture practices for this species in alpine regions.