High-temperature stress has become an important factor that has restricted the aquaculture industry. Huso dauricus is a high-economic-value fish that has faced the threat of thermal stress. Based on this point, our investigation aimed to explore the detailed mechanism of the negative impacts of heat stress on the liver metabolism functions in Huso dauricus. In this study, we set one control group (19 °C) and four high-temperature treatment groups (22 °C, 25 °C, 28 °C, 31 °C) with 40 fish in each group for continuous 53-day heat exposure. Histological analysis, biochemical detection, and transcriptome technology were used to explore the effects of heat stress on the liver structure and functions of juvenile Huso dauricus. It suggested heat-stress-induced obvious liver injury and reactive oxygen species accumulation in Huso dauricus with a time/temperature-dependent manner. Serum total protein, transaminase, and alkaline phosphatase activities showed significant changes under heat stress (p < 0.05). In addition, 6433 differentially expressed genes (DEGs) were identified based on the RNA-seq project. Gene Ontology enrichment analysis showed that various DEGs could be mapped to the lipid-metabolism-related terms. KEGG enrichment and immunohistochemistry analysis showed that ferroptosis and FoxO signaling pathways were significantly enriched (p < 0.05). These results demonstrated that thermal stress induced oxidative stress damage in the liver of juvenile Huso dauricus, which triggered lipid metabolism disorder and hepatocyte ferroptosis to disrupt normal liver functions. In conclusion, chronic thermal stress can cause antioxidant capacity imbalance in the liver of Huso dauricus to mediate the ferroptosis process, which would finally disturb the lipid metabolism homeostasis. In further research, it will be necessary to verify the detailed cellular signaling pathways that are involved in the heat-stress-induced liver function disorder response based on the in vitro experiment, while the multi-organ crosswalk mode under the thermal stress status is also essential for understanding the comprehensive mechanism of heat-stress-mediated negative effects on fish species.

The present study aimed to explore whether water flow velocity could affect the swimming ability and overall energy metabolism of wild Amur grayling (Thymallus grubii). Swimming performance was assessed by measuring critical swimming speed (U_crit), burst speed (U_burst), and oxygen consumption rate (MO₂) based on the stepped velocity test method. Our results showed that the absolute values of U_crit and U_burst tended to increase with body length. In contrast, the relative values of U_crit and U_burst tended to decrease and increase, respectively. MO₂ in Amur grayling was elevated with increasing velocity, suggesting relatively high swimming efficiency. We also measured the biochemical indices related to energy metabolism. Lactate dehydrogenase, hexokinase, and pyruvate kinase activities significantly increased (p < 0.05). Hepatic glycogen, glucose, and muscle glycogen contents decreased with the increasing trend of velocity (p < 0.05), the lactic acid contents of the blood and muscles increased significantly with the increase in velocities (p < 0.05), and changes in creatine phosphate content showed no significant difference (p > 0.05). The results not only denote the relationship between body size and swimming speed but also show the effects of water flow velocity on energy metabolism in Amur grayling. The results provide basic data for the construction of fish passage.

Alkaline water is toxic to cultured aquatic animals that frequently live in pH-neutral freshwater. Overfishing and habitat destruction have contributed to the decline in the wild sturgeon population; consequently, the domestic hybrid sturgeon has become an increasingly important commercial species in China. Hybrid sturgeons are widely cultured in alkaline water, but little is known about the effects of alkalinity stress on hybrid sturgeon liver tissues. We exposed hybrid sturgeons to four alkaline concentrations (3.14 ± 0.02 mmol/L, 7.57 ± 0.08 mmol/L, 11.78 ± 0.24 mmol/L and 15.46 ± 0.48 mmol/L). Histopathology, biochemical index assessment, gene expression level detection and metabolomics analysis were used to investigate the negative effects on liver functions following exposure to NaHCO₃. Livers exposed to alkaline stress exhibited severe tissue injury and clear apoptotic characteristics. With increased exposure concentrations, the hepatic superoxide dismutase, catalase, glutathione peroxidase and alkaline phosphatase activities significantly decreased in a dose-dependent manner. NaHCO₃ exposure up-regulated the transcriptional levels of apoptosis/ferroptosis-related genes in livers. Similarly, the expression trends of interleukin-1β and heat shock protein genes also increased in high-alkalinity environments. However, the expression levels of complement protein 3 significantly decreased (p < 0.05). Hepatic untargeted metabolomics revealed the alteration conditions of various metabolites associated with the antioxidant response, the ferroptosis process and amino acid metabolism (such as beta-alanine metabolism; alanine, aspartate and glutamate metabolism; and glycine, serine and threonine metabolism). These data provided evidence that NaHCO₃ impaired immune functions and the integrity of hybrid sturgeon liver tissues by mediating oxidative-stress-mediated apoptosis and ferroptosis. Our results shed light on the breeding welfare of domestic hybrid sturgeons and promote the economic development of fisheries in China.

Temperature fluctuations caused by climate change and global warming pose a threat to fish. The burbot (lota lota) population is particularly sensitive to increased water temperature, but the systematic impacts of high-temperature exposure on their liver and intestinal health remain unclear. In January of 2025, we collected wild adult burbot individuals from the Ussuri River (water temperature: about 2 °C), China. The burbot were exposed to 2 °C, 7 °C, 12 °C, 17 °C, and 22 °C environments for 96 h; then, the liver and intestinal contents were subsequently collected for histopathology observation, immunohistochemistry, biochemical index assessment, and transcriptome/16S rDNA sequencing analysis. There was obvious liver damage including hepatocyte necrosis, fat vacuoles, and cellular peripheral nuclei. Superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities were elevated and subsequently decreased. Additionally, the malondialdehyde (MDA) level significantly increased with increasing temperature. These results indicate that 7 °C (heat stress temperature), 12 °C (tipping point for normal physiological metabolism status), 17 °C (tipping point for individual deaths), and 22 °C (thermal limit) are critical temperatures in terms of the physiological response of burbot during their breeding period. In the hepatic transcriptome profiling, 6538 differentially expressed genes (DEGs) were identified, while KEGG enrichment analysis showed that high-temperature stress could affect normal liver function by regulating energy metabolism, immune, and apoptosis-related pathways. Microbiomics also revealed that acute heat stress could change the intestinal microbe community structure. Additionally, correlation analysis suggested potential regulatory relationships between intestinal microbe taxa and immune/apoptosis-related DEGs in the liver. This study revealed the potential impact of environmental water temperature changes in cold habitats in winter on the physiological adaptability of burbot during the breeding period and provides new insights for the ecological protection of burbot in the context of global climate change and habitat warming.

The sturgeon population has experienced strict threats due to inordinate human activities in the last decade and has been classified into the Red List of Threatened Species in recent years. Stock enhancement is one effective practice for the conservation of wild sturgeons. However, the survival conditions for sturgeon were not satisfactory after they were directly restocked into their natural habitat. Huso dauricus is an important protected sturgeon species, and finding an appropriate conservation strategy for the wild population is urgent. To clarify the dynamic adaptability of Huso dauricus to its wild environment, 1000 individuals were released into a natural river. On the 0th, 7th, 14th, and 30th days, five recaptured individuals were used to evaluate the dynamic trends in biochemical biomarkers, intestinal histomorphology, gut microbe taxon composition, and transcription profile over 30 days of stock enhancement. Our results indicated that Huso dauricus individuals still had a physiological stress status on the seventh day and then gradually adapted to the wild habitat 14 days after reintroduction based on the serum cortisol level. Meanwhile, the feeding habitat, organ function indicators, and growth performance showed similar dynamic changes within 30 days. Interestingly, their gut bacterial diversity and taxon structure also fluctuated over the 30 days after restocking, and they were accompanied by dynamic changes in intestinal pathological injury and tight junction protein expression in this period. The transcriptome analysis revealed the dynamic adaptability of Huso dauricus to wild habitats associated with the expression modes of genes related to the FoxO family, immune system, cytochrome family, and ATP metabolism. Taken together, the findings of the present research demonstrated that artificial reintroduction had dynamic impacts on the health condition of Huso dauricus and that 14 days of wilderness training might be essential for sturgeon restocking practices. Our study revealed the adaption mechanism of Huso dauricus at the molecular level during the restocking period and shed light on the theoretical guidelines for wild sturgeon conservation.

Ammonia nitrogen is a common contaminant in aquatic environments, and its potential toxicity to organisms has attracted extensive attention. However, few studies have comprehensively evaluated the negative impacts of ammonia stress on cold-water fish. In this study, liver, gill, and intestine specimens of Amur grayling (Thymallus grubii) from three treatment groups (control (0 mg/L), low ammonia (43.683 mg/L), and high ammonia (436.8 mg/L)), were collected for histological observation, biochemical examination, and transcriptomic, metabolomic, and intestinal microbiome analysis. Our results showed that excessive ammonia nitrogen blocked the normal immune function and compromised the integrity of liver and gill tissues through oxidative stress-mediated differential cell death pathways. Meanwhile, the multi-omics analysis revealed that ammonia exposure predominantly altered the carbohydrate, lipid, and amino acid metabolism modes. In addition, it was also demonstrated that ammonia nitrogen stress affected the composition of intestinal microbiota taxa. This study provides insights into the potential risks and hazards of ammonia stress on cold fish in natural waters and provides a reference for the environment control of the water quality in aquaculture.