Effects of acclimation temperature regime on the thermal tolerance, growth performance and gene expression of a cold-water fish, Schizothorax prenanti

Physiological responses to different temperature in the liver of Takifugu rubripes larvae revealed by integrated transcriptomic and metabolomic analyses

Water temperature plays a vital role in shaping the physical conditions crucial for the growth, development and reproduction of fish species. Since limited comprehensive multi-omics analyses exploring the molecular mechanisms of temperature influences on the early life stages of fish. Here, the effects of temperature variations on the growth of Takifugu rubripes, a commercial teleost farmed in Asia were investigated. Nineteen-days-old fugu larvae were subjected to different temperature (15 °C-T15, 20 °C-T20, 25 °C-T25) for 30 days. Liver tissues were harvested at the end of the study for transcriptomic and metabolomic assessments. The T. rubripes larvae in the T15 group showed a significant decrease in total length and body weight compared to the T20 and T25 groups (p < 0.05). 1344, 416, and 2080 differentially expressed genes (DEGs) were identified in T15-vs-T20, T20-vs-T25, and T15-vs-T25 comparisons, respectively. Those DEGs were mainly enriched in metabolic, protein digestion and absorption, steroid biosynthesis, and glycerophospholipid metabolism pathways. 15 DEGs were randomly selected for RNA-seq validation, and the transcriptome results were consistent with the qPCR validation results, illustrating the accuracy of transcriptome sequencing. 340, 238, and 330 significantly different metabolites (SDMs) were identified in positive modes when comparing in T15-vs-T20, T20-vs-T25, and T15-vs-T25, respectively. Additionally, 145, 137, and 159 SDMs were identified in negative modes within the three comparisons. Those SDMs enriched in biosynthesis of secondary metabolites, glycerophospholipid metabolism, linoleic acid metabolism, and metabolic pathways. The integration of transcriptomic and metabolomic analyses indicated that DEGs and SDMs mainly enriched in metabolic pathways. These discoveries provide valuable insights into the effects of temperature on fish larvae in aquaculture, laying a foundation for future breeding approaches aimed at improving the growth of T. rubripes.

Constraints of digestion on swimming performance and stress tolerance vary with habitat in freshwater fish species

Limited aerobic scope (AS) during digestion might be the main constraint on the performance of bodily functions in water-breathing animals. Thus, investigating the postprandial changes in various physiological functions and determining the existence of a shared common pattern because of possible dependence on residual AS during digestion in freshwater fish species are very important in conservation physiology. All species from slow-flow habitats showed impaired swimming speed while digesting, whereas all species from fast-flow habitats showed strong swimming performance, which was unchanged while digesting. Only two species from slow-flow habitats showed impaired heat tolerance during digestion, suggesting that whether oxygen limitation is involved in the heat tolerance process is species-specific. Three species from slow- or intermediate-flow habitats showed impaired hypoxia tolerance during digestion because feeding metabolism cannot cease completely under hypoxia. Overall, there was no common pattern in postprandial changes in different physiological functions because: (1) the digestion process was suppressed under oxygen-limiting conditions, (2) the residual AS decreased during digestion, and (3) performance was related to residual AS, while digestion was context-dependent and species-specific. However, digestion generally showed a stronger effect on bodily functions in species from slow-flow habitats, whereas it showed no impairment in fishes from fast-flow habitats. Nevertheless, the postprandial change in physiological functions varies with habitat, possibly due to divergent selective pressure on such functions. More importantly, the present study suggests that a precise prediction of how freshwater fish populations will respond to global climate change needs to incorporate data from postprandial fishes.

Influence of salinity on the thermal tolerance of aquatic organisms

Aquatic organisms are challenged by changes in their external environment, such as temperature and salinity fluctuations. If these variables interacted with each other, the response of organisms to temperature changes would be modified by salinity and vice versa. We tested for potential interaction between temperature and salinity effects on freshwater, brackish, and marine organisms, including algae, macrophytes, heterotrophic protists, parasites, invertebrates, and fish. We performed a meta-analysis that compared the thermal tolerance (characterised by the temperature optimum, lower and upper temperature limits, and thermal breadth) at various salinities. The meta-analysis was based on 90 articles (algae: 15; heterotrophic protists: 1; invertebrates: 43; and fish: 31). Studies on macrophytes and parasites were lacking. We found that decreasing salinity significantly increased and decreased the lower and upper temperature limits, respectively, in all groups. Thus, a lowered salinity increased the thermal sensitivity of organisms. These findings mainly reflect the response of brackish and marine organisms to salinity changes, which dominated our database. The few studies on freshwater species showed that their lower thermal limits increased and the upper thermal limits decreased with increasing salinity, albeit statistically nonsignificant. Although non-significant, the response of thermal tolerance to salinity changes differed between various organism groups. It generally decreased in the order of: algae > invertebrates > fish. Overall, our findings indicate adverse effects of salinity changes on the temperature tolerance of aquatic organisms. For freshwater species, studies are comparatively scarce and further studies on their thermal performance at various salinity gradients are required to obtain more robust evidence for interactions between salinity and temperature tolerance. Considering test conditions such as acclimation temperature and potential infection with parasites in future studies may decrease the variability in the relationship between salinity and thermal tolerance.

Magical role of iron nanoparticles for enhancement of thermal efficiency and gene regulation of fish in response to multiple stresses

The present study addresses the challenges of uncontrolled temperature and pollution in aquatic environments, with a focus on fish ability to tolerate high temperature. The investigation aimed to determine the role of iron nanoparticles (Fe-NPs) in enhancing the thermal tolerance of Pangasianodon hypophthalmus exposed to high-temperature stress, arsenic (As), and ammonia (NH3) toxicity. Fe-NPs were synthesized using green approaches, specifically from fish gill. The dietary Fe-NPs were formulated and supplemented at 10, 15, and 20 mg kg⁻1 of feed. Notably, Fe-NPs at 15 mg kg⁻1 diet significantly reduced the critical thermal minimum (CTmin) (14.44 ± 0.21 °C) and the lethal thermal minimum (LTmin) (13.46 ± 0.15 °C), compared to the control and other treatment groups. Conversely, when Fe-NPs at 15 mg kg⁻1 were supplemented with or without exposure to stressors (As + NH3+T), the critical thermal maximum (CTmax) increased to 47.59 ± 0.16 °C, and the lethal thermal maximum (LTmax) increased to 48.60 ± 0.37 °C, both significantly higher than the control and other groups. A strong correlation was observed between LTmin and CTmin (R2 = 0.90) and between CTmax and LTmax (R2 = 0.98). Furthermore, dietary Fe-NPs at 15 mg kg⁻1 significantly upregulated the expression of stress-related genes, including HSP70, iNOS, Caspase-3a, CYP450, MT, cat, sod, gpx, TNFα, IL, TLR, and Ig. The enhanced thermal tolerance (LTmin and LTmax) can be attributed to these gene regulations, suggesting the mechanistic involvement of Fe-NPs in improving thermal resilience. Overall, the findings demonstrate that dietary supplementation with Fe-NPs, particularly at 15 mg kg⁻1, improves thermal tolerance and stress response in P. hypophthalmus by enhancing gene expression and overall thermal efficiency under stressor conditions.

The effects of the predictability of acclimatory temperature on the growth and thermal tolerance of juvenile Spinibarbus sinensis

Heated effluent injection, cold hypolimnetic water inputs from dams, and extreme weather events can lead to unpredictable temperature fluctuations in natural waters, impacting fish performance and fitness. We hypothesized that fish exposed to such unpredictable fluctuations would exhibit weaker growth and enhanced thermal tolerance compared to predictable conditions. Qingbo (Spinibarbus sinensis) was selected as the experimental subject in this study. The qingbo were divided into a constant temperature group (C, 22 ± 0.5 °C), a predictable temperature fluctuation group (PF, 22 ± 4 °C, first warming, then cooling within a day) and an unpredictable temperature fluctuation group (UF, 22 ± 4 °C, the order of warming or cooling is random). After 40 days of temperature acclimation, the growth, metabolic rate, spontaneous activity, thermal tolerance, plasma cortisol concentration and liver hsp70 level of the fish were measured. Unexpectedly, neither the PF nor the UF group showed decreased growth compared to the C group. This could be attributed to the fact that temperature variation did not lead to a substantial increase in basic energy expenditure. Furthermore, feeding rates increased due to temperature fluctuations, although the difference was not significant. Both the PF and UF groups exhibited increased upper thermal tolerance, but only the UF group exhibited improved lower thermal tolerance and higher liver hsp70 levels compared to the C group. The qingbo that experienced unpredictable temperature fluctuations had the best thermal tolerance among the 3 groups, which might have occurred because they had the highest level of hsp70 expression. This may safeguard fish against the potential lethal consequences of extreme temperatures in the future. These findings suggested that qingbo exhibited excellent adaptability to both predictable and unpredictable temperature fluctuations, which may be associated with frequent temperature fluctuations in its natural habitat.

Influence of increasing acclimation temperature on growth, digestion, antioxidant capacity, liver transcriptome and intestinal microflora of Ussruri whitefish Coregonus ussuriensis Berg

For effective restoration, conservation of Ussruri whitefish Coregonus ussuriensis Berg and coping with global climate change, effects of environmental temperature on Ussruri whitefish urgently need to be explored. In current study, the effects of different acclimation temperatures on the growth, digestive physiology, antioxidant ability, liver transcriptional responses and intestinal microflora patterns of Ussruri whitefish were investigated. Ussruri whitefish (15.20 g ± 1.23 g) were reared for 42 days under different acclimation temperatures, i.e., 10, 13, 16, 19, 22 and 25 °C, respectively. Result first determined 28 °C as the semi-lethal temperature in order to design the temperature gradient test. Highest main gain rate (MGR) and specific growth rate (SGR) were observed in fish group having acclimation temperature of 19 °C. Significantly decrease (P < 0.05) in triglyceride (TG) content appeared at 19 °C as compared to the 10 °C and 13 °C temperature groups. 19 °C notablely increased protease activities of stomach and intestine and intestinal lipase and amylase activities. 19 °C group obtained the highest activities of chloramphnicol acetyltransferase (CAT) and total antioxidant capacity (T-AOC) and higher activities of superoxide dismutase (SOD). The intestinal microflora composition was most conducive to maintaining overall intestinal health when the temperature was 19 °C, compared to 10 °C and 25 °C. Ussruri whitefish exposed to 10 °C and 25 °C possessed the lower Lactobacillus abundance compared to exposure to 19 °C. Temperature down to 10 °C or up to 25 °C, respectively, triggered cold stress and heat stress, which leading to impairment in intestinal digestion, liver antioxidant capacity and intestinal microflora structure. Liver transcriptome response to 10 °C, 19 °C and 25 °C revealed that Ussruri whitefish might require the initiation of endoplasmic reticulum stress to correct protein damage from cold-temperature and high-temperature stress, and it was speculated that DNAJB11 could be regarded as a biomarker of cold stress response.Based on the quadratic regression analysis of MGR and SGR against temperature, the optimal acclamation temperature were, respectively, 18.0 °C and 18.1 °C. Our findings provide valuable theoretical insights for an in-depth understanding of temperature acclimation mechanisms and laid the foundation for conservation and development of Ussruri whitefish germplasm resources.

Daily thermal variability does not modify long-term gene expression relative to stable thermal environments: A case study of a tropical fish

Global warming is leading to an increase in the frequency and intensity of extreme weather events, magnifying the breadth of temperatures faced by ectotherms across days and seasons. Despite the importance and ecological relevance of diurnal thermal variability, the vast majority of knowledge on gene expression patterns and physiology stems from animals acclimated to constant temperatures or in the early stages of exposure to a new temperature regime. If heterothermal environments modulate responses differently from constant thermal environments, our existing capacity to forecast impacts of climate warming may be compromised. To address this knowledge gap, we acclimated barramundi (Lates calcarifer) to 23 °C, 29 °C (optimal), 35 °C and to thermal cycling conditions (23-35 °C daily with a mean of 29 °C) and sampled liver and white muscle tissue before acclimation and after 2 and 17 weeks of acclimation. NanoString nCounter technologies were used to measure expression of 20 genes related to metabolism, growth and maintenance of cellular homeostasis. Acclimation to cool and warm conditions caused predictable changes in whole-animal performance (metabolism and growth) and the underlying gene expression patterns. Acclimation to a cycling temperature regime did not change the molecular regulation of metabolism or growth compared with barramundi acclimated to constant 29 °C, nor did it cause any discernible effects on whole-animal performance. However, the heat shock response was higher in the former group, suggesting that barramundi under a daily temperature cycle have an increased need for cellular chaperoning to minimise detrimental effects of temperature on proteins. We conclude that the genetic regulation of metabolism and growth may be more dependent on the mean daily temperature than on the daily temperature range.

Redox state and metabolic responses to severe heat stress in lenok Brachymystax lenok (Salmonidae)

In order to provide new insights into the physiological responses of lenok (Brachymystax lenok: Salmonidae) to acute and severe heat stress (25°C, 48 h), dynamic changes in redox state and metabolic responses are studied combined biochemical index and non-targeted metabolome. Nicotinamide adenine dinucleotide (NAD⁺) consumption causes significant increases in ratio of reduced NADH to NAD⁺ and ratio of reduced nicotinamide adenine dinucleotide phosphate (NADPH) to NADP⁺, which induced the redox imbalance in heat stressed lenok. Lowered reduced glutathione/oxidized glutathione (GSH/GSSG) ratios suggested that more oxidized conditions occurred in heat-stressed lenok, leading to membrane lipid oxidation. The first few hours of heat stress promoted the activity of enzymes involved in anaerobic glycolysis (hexokinase, pyruvate kinase, lactic dehydrogenase) and glutamicpyruvic transaminase and glutamic oxaloacetic transaminase, which might lead to consumption of many carbohydrates and amino acid catabolism. These enzyme activities decreased with time in a possible compensatory strategy to manage anabolic and catabolic metabolism, maintaining the redox homeostasis. After 48 h of recovery, NAD⁺, carbohydrate levels and enzyme activities had returned to control levels, whereas many amino acids were consumed for repair and new synthesis. GSH remained at levels lower than controls, and the more oxidized conditions had not recovered, aggravating oxidative damage. Glutamic acid, glutamine, lysine and arginine may play important roles in survival of heat-stressed lenok.

Thermal Stress Induces Metabolic Responses in Juvenile Qingtian Paddy Field Carp Cyprinus carpio var qingtianensis

Extreme fluctuations in water temperature lead to significant economic losses for the aquaculture industry. Cyprinus carpio var qingtianensis (locally called Qingtian paddy field carp), is a local variety commonly found in Zhejiang province, China. Unlike traditional aquaculture environments, the water temperature range between day and night in the rice field environment is much larger, and the high temperature in summer may exceed the growth threshold of fish because there is no manual intervention; therefore, the study of how the Qingtian paddy field carp (PF carp) adapts to high-temperature conditions can shed light how the species adapt to the rice field environment. To investigate the molecular mechanisms of this fish under thermal stress, the liver metabolomics of Qiangtian paddy field carp (PF carp) were analyzed. In this study, metabolomics was used to examine the metabolic reaction of PF carp (102 days old, 104.69 ± 3.08 g in weight, 14.65 ± 0.46 cm in length) at water temperatures of 28 °C (control group, CG), 34 °C (experimental group (EG) 34), and 38 °C (EG38). The results show that 175 expression profile metabolites (DEMs), including 115 upregulated and 60 downregulated metabolites, were found in the CG vs. EG34. A total of 354 DEMs were inspected in CG vs. EG38, with 85 metabolites downregulated and 269 metabolites upregulated. According to the pathway enrichment study, various pathways were altered by thermal stress, including those of lipid, amino-acid, and carbohydrate metabolism. Our study presents a potential metabolic profile for PF carp under thermal stress. It also demonstrates how the host responds to thermal stress on a metabolic and molecular level.

Physiological responses to heat stress in the liver of rainbow trout (Oncorhynchus mykiss) revealed by UPLC-QTOF-MS metabolomics and biochemical assays

Rainbow trout (Oncorhynchus mykiss) is one of the world's most widely farmed cold-water fish. However, the rise in water temperature caused by global warming has seriously restricted the development of rainbow trout aquaculture. In this study, we investigated the physiological responses in the liver of rainbow trout exposed to 20 ℃ and 24 ℃ and returning to the initial temperature (14 ℃) by combining biochemical analyses and UPLC-QTOF-MS metabolomics. The results of the biochemical analysis showed that serum aminotransferase, lysozyme, total bilirubin, alkaline phosphatase and liver superoxide dismutase, glutathione peroxidase, and malondialdehyde in rainbow trout under heat stress changed significantly. Even after the temperature recovery, some of the above indicators were still affected. Compared to the control group, 115, 130, and 121 differentially expressed metabolites were identified in the 20 ℃, 24 ℃, and recovery groups, respectively. Further pathway enrichment of these metabolites revealed that heat stress mainly affected the linoleic acid metabolism, α-linolenic acid metabolism, glycerophospholipid metabolism, and sphingolipid metabolism in the liver of rainbow trout, and continuously affected these metabolic pathways during the recovery period. Notably, the enrichment of glutathione metabolic pathways was consistent with the changes in glutathione peroxidase in the biochemical results. The results above suggest that heat stress can induce immune responses and oxidative stress inside the rainbow trout. After temperature recovery, some of the hepatic functions of fish return to normal gradually. The biochemical analysis and UPLC-QTOF-MS metabolomics tools provide insight into the physiological regulation of rainbow trout in response to heat stress.

Effects of early low temperature exposure on the growth, glycolipid metabolism and growth hormone (gh) gene methylation in the late stage of Chinese perch (Siniperca chuatsi)

Temperature is an important factor affecting the early development, growth and physiology of fish, as well as on aspects of feeding and metabolism. Here, we investigated the impact of low temperature on the growth, glycolipid metabolism and growth hormone (gh) gene methylation in the late stage of Chinese perch (Siniperca chuatsi). Chinese perch larvae were exposed to temperatures with 21 °C (low temperature group (LT)) and 25 °C (control group) for 7 days, and then the LT group was slowly heated to 25 °C and raised at this temperature for two months. Results indicated that the LT group exhibited significantly lower growth rate and weight gain rate than the control group (p < 0.05), but no obvious food intake (FI) were detected yet between LT group and control group. The larvae exposed at 21 °C relative to the 25 °C group had significant decreased transcript levels of GH-IGF axis genes (gh, igf1 and igf2) in Chinese perch juvenile (p < 0.05). Further analysis of the DNA methylation levels of gh showed that the LT group had higher at the CpG sites of -3029 and - 3032 than the control group in larvae (p < 0.05), whereas the DNA methylation levels at CpG sites of -2982 and - 3039 of gh were significantly lower compared with the control group in juveniles (p < 0.05). In addition, the plasma glucose was significantly increased in the LT group (p < 0.05), suggesting the metabolism of blood glucose slowed at low temperature. In larvae, the expressions of glycolipid metabolism genes (ins-ra and ins-rb) in LT group were significantly up-regulated compared to control group in larvae (p < 0.05), while down-regulated in juveniles (p < 0.05). The expression level of ucp2 mRNA was continuously up-regulated under low temperature stress. All these data demonstrate that early exposure to low temperature affected the growth and glycolipid metabolism of Chinese perch.