Rhinogobio ventralis is a typical endemic fish and an important economic species in the upper reaches of the Yangtze River. However, it is highly susceptible to Ichthyophthirius multifiliis (Ich) during artificial breeding, resulting in elevated mortality rates following infection. In this study, we established an infection model using Ich to investigate its effects on the skin of R. ventralis. Pathological changes on the skin were examined through tissue sections and transmission electron microscopy. The results showed a significant increase in mucus cells, club cells and epidermal thickness, the abnormal desmosome junction between epithelial cells, mucous cells pyknosis shrinkage along with morphological and structural abnormalities in their organelles within the skin after infection. We employed transcriptomics and metabolomics to characterize key genes, metabolites, and signaling pathways in the skin following Ich infection. A total of 84,016 unigenes and 1075 metabolites were obtained from skin tissues. Respectively, 388 DEGs and 135 differentially expressed metabolites, 233 DEGs and 72 differentially expressed metabolites were obtained at 7 dpi and 14 dpi, respectively. In response to Ich infection, the host modifies the ribosome pathway, protein processing in endoplasmic reticulum pathway, antigen processing and presentation pathway and glycerophospholipid metabolism, which suggests both disruption and activation of the immune system, alongside disruptions in metabolic processes among infected R. ventralis. Our results shed light on the immune strategies employed by R. ventralis in response to Ich infections, thereby providing a valuable dataset for further investigation into the mechanisms underlying resistance regulation in R. ventralis against such infections.

To explore a safe and effective approach for producing strontium-enriched fish, in this study, we modified the feed for juvenile hybrid sturgeon (Acipenser baerii ♀ × Acipenser schrenckii ♂) and set three different levels of strontium chloride content in their diet (0 mg/kg (Sr0, control), 80 mg/kg (Sr80), and 160 mg/kg (Sr160)) for a period of 8 weeks, analyzing their growth performance, strontium enrichment, muscle nutrition, and hepatic physiological, biochemical, and transcriptomic characteristics. The results show that dietary strontium had no significant impact on sturgeon growth or survival rate (p > 0.05). The strontium content in tissues increased with dietary strontium levels, with the highest enrichment in bone plates (p < 0.05). However, muscle crude fat in the strontium-supplemented groups decreased significantly; the Sr160 group had higher glutamic acid, valine, docosahexaenoic acid methyl ester, lower myristic acid, palmitic acid, etc. (p < 0.05). In addition, strontium treatment alleviated hepatic lipid accumulation and mitochondrial swelling. Biochemical analyses revealed reduced plasma levels of Triglyceride (TG), Total Cholesterol (TC), Alanine Aminotransferase (ALT), and Aspartate Aminotransferase (AST), as well as decreased hepatic Malondialdehyde (MDA) content, while hepatic Glutathione (GSH) levels increased (p < 0.05). Transcriptomic data further showed that strontium downregulated the expression of fasn and tfrc and upregulated the expression of cpt1a, apoa1, cyp7a1, and slc3a2 (p < 0.05). In conclusion, dietary supplementation with 80–160 mg/kg strontium enables safe strontium enrichment in hybrid sturgeon, improves muscle nutritional quality, and protects liver function by regulating the genes related to lipid metabolism and antioxidant defense, providing a scientific basis for the development of strontium-enriched fish products.

Sichuan bream (Sinibrama taeniatu), an endemic small economic fish in the upper Yangtze River, has achieved captive breeding breakthroughs. To advance standardized and large-scale aquaculture, this study investigated intestinal development, enzyme activities, gut microbiota, and its interactions with rearing water microbiota across six developmental stages (G1–G6) from hatching to sexual maturity of Sichuan bream. Results showed its progressive refinement of external morphology and intestinal developing into multiple flexures. Histology examination revealed four foregut layers with continuously increasing villus height. Digestive enzyme analysis revealed significantly higher activity of trypsin compared to that of amylase and lipase (p < 0.05). 16S rRNA sequencing identified Proteobacteria, Firmicutes, Bacteroidota, Actinobacteriota, and Fusobacteria as the dominant phyla in both gut and rearing water microbiota. Gut communities shifted from Proteobacteria-dominance (C₁–C₅) to Firmicutes-dominance (C6). The microbial source tracking analysis indicated water contributed to gut microbiota of Sichuan bream, particularly during G3. This study clarified the intestinal development patterns and gut microbiota colonization dynamics of Sichuan bream. The findings provide reference materials for the research on the growth patterns and host–microbe interaction of Sichuan bream. They lay a theoretical foundation for the protection and utilization of Sichuan bream resources, ultimately aiding in their proliferation and release.

The endangered Rhinogobio ventralis, endemic to the upper Yangtze River, is dependent on captive breeding for its conservation. However, this highly stress-sensitive species is exceptionally susceptible to Ichthyophthirius multifiliis, leading to severe pathology and high mortality in culture. Elevated salinity holds potential for managing key aquaculture pathogens, including Ichthyophthirius multifiliis and Saprolegnia spp. However, its potential unintended ecological consequences remain insufficiently understood. This study evaluated the systemic impacts of 5‰ salinity on the culture environment of the endangered species Rhinogobio ventralis, using integrated 16S/18S rRNA gene sequencing and water quality analysis. The results demonstrated that while salinity treatment effectively reduced the environmental molecular signal of harmful eukaryotes such as Ichthyophthirius and Saprolegnia, it also induced significant ecological shifts: (1) aquatic prokaryotic diversity increased, yet the self-purification capacity of the water was compromised, indicated by elevated dissolved oxygen, nitrate nitrogen, and total nitrogen; (2) in the fish intestinal microbiome, a decline in potentially beneficial taxa (e.g., Exiguobacterium) co-occurred with an enrichment of genera containing potentially pathogenic species (e.g., Staphylococcus and Pseudomonas), collectively suggesting a state of dysbiosis; (3) co-occurrence network analysis revealed that the aquatic microbial community developed greater complexity, while the intestinal network became structurally simplified and more antagonistic. These findings reveal that elevating salinity in freshwater aquaculture systems compromises both host microbiome health and aquatic ecosystem functioning. As such, future aquaculture management should integrate supportive measures like probiotic supplementation to maintain overall system stability.

Sperm cryopreservation is pivotal for conserving fish germplasm, yet cryodamage-induced quality decline limits its application. This study focused on Sichuan bream (Sinibrama taeniatus), an endemic and economically important fish species in the upper Yangtze River. Based on an established cryopreservation protocol, we evaluated sperm quality using computer-assisted sperm analysis (CASA) and fertility assays, followed by a systematic assessment of structural and functional damage via flow cytometry (membrane integrity, mitochondrial potential, reactive oxygen species, and DNA fragmentation), enzymatic assays (energy metabolism and antioxidant enzymes), Western blotting, and ultrastructural observation. Finally, integrated proteomic and metabolomic analyses were employed to elucidate the underlying physiological mechanisms. The results demonstrated that freeze–thawing significantly impaired sperm motility, fertility, and ultrastructure, concurrently disrupting energy metabolism and the antioxidant system. Crucially, multi-omics revealed that these functional declines were linked to dysregulation in key pathways involving cytoskeleton organization, lipid metabolism, energy homeostasis, and oxidative stress, forming a coherent network from initial molecular perturbation to phenotypic dysfunction. This study provides a comprehensive characterization of sperm cryodamage in Sichuan bream, advancing the understanding of fish sperm cryobiology and informing targeted cryoprotection strategy development.

Hybridization is pivotal for germplasm innovation, yet how reciprocal crossing regulates digestive characteristics in sub-cold-water fish remains unclear. This study systematically compared differences in intestinal morphology, physiological function, and microbial community assembly among herbivorous Schizothorax prenanti, carnivorous S. davidi, and their reciprocal hybrids using histological analysis, digestive enzyme assays, and 16S rRNA sequencing. Results indicated that parental intestinal characteristics were highly consistent with their feeding habits. Orthogonal hybrids exhibited a mosaic phenotype, combining the maternal muscular gut structure with high paternal-like lipase activity, and were characterized by an enrichment of the potential probiotic Lactococcus. In contrast, reciprocal hybrids presented a mismatch between morphology and function: despite developed hindgut folds, key digestive enzyme activities were low, and the gut microbiota was dominated by environmental bacteria such as Methylobacterium. Our findings indicate a spatially dependent assembly dynamic: the host genetic background strongly drives microbiome divergence in the anterior segments (foregut and midgut), whereas the long-term administration of a standardized diet ultimately promotes structural convergence in the hindgut. The orthogonal cross yielded a phenotype characterized by an apparent co-occurrence of specific host enzymes and distinct microbiota, suggesting an inferred physiological potential for lipid digestion that requires further multi-omics validation. These findings provide preliminary insights into the associations between genetic background and intestinal traits, providing a theoretical basis for the targeted breeding of Schizothorax species.