Growth rate, catalase and superoxide dismutase activities in rock carp (Procypris rabaudi Tchang) exposed to supersaturated total dissolved gas

Molecular mechanisms of physiological change under acute total dissolved gas supersaturation stress in yellow catfish (Pelteobagrus fulvidraco)

During the dam discharging period, the strong aeration of high-speed water leads to the supersaturation of total dissolved gas (TDG) in the downstream water, which causes gas bubble disease (GBD) in fish and threatens their survival. TDG supersaturation has now become an ecological and environmental issue of global concern; however, the molecular mechanism underlying the physiological effect of TDG supersaturation on fish is poorly known. Here, we comprehensively investigated the effect of TDG supersaturation on Pelteobagrus fulvidraco at the histopathological, biochemical, transcriptomic, and metabolomic levels. After exposure to 116% TDG, P. fulvidraco exhibited classic GBD symptoms and pathological changes in gills. The level of superoxide dismutase was highly significantly decreased. Transcriptomic results revealed that heat shock proteins (HSPs) and a large number of genes involved in immunity were increased by TDG stress. A key environmental sensor PI3K/Akt/mTOR pathway was significantly stimulated for defence against stress. Integrated transcriptomic and metabolomic analyses revealed that key metabolites and genes were upregulated in the triacylglycerol synthesis pathway and that amino acid levels decreased, which might be associated with TDG supersaturation stress. The present study demonstrated that TDG supersaturation could cause severe physiological damage in fish. HSP genes, immune functions, and energy metabolic pathways were enhanced to counteract the adverse effects.

Comparative transcriptome analysis provides insights into the TDG supersaturation stress response of Schizothorax davidi

In the dam discharge season, the supersaturation of total dissolved gas (TDG) in the downstream channel can seriously affect the survival of aquatic organisms. However, few studies have revealed the mechanism by which TDG supersaturation affects the physiology of fish thus far. The present study was conducted to study the mechanism of the effect of TDG supersaturation on Schizothorax davidi, a species that is very sensitive to gas bubble disease. S. davidi was exposed to 116 % TDG supersaturation stress for 24 h. Serum biochemical tests showed that the aspartate aminotransferase and alanine aminotransferase levels after TDG supersaturation exposure were significantly decreased compared to those in the control group, while superoxide dismutase activity was significantly increased. RNA-Seq of gill tissues identified 1890 differentially expressed genes (DEGs), which consisted of 862 upregulated genes and 1028 downregulated genes, in the TDG supersaturation group vs. the control group. Pathway enrichment analysis revealed that the cell cycle, apoptosis and immune signaling pathways were affected by TDG stress. The results of this study may contribute to our understanding of the underlying molecular mechanism of environmental stress in fish.

Biochemical, transcriptomic and metabolomic responses to total dissolved gas supersaturation and their underlying molecular mechanisms in Yangtze sturgeon (Acipenser dabryanus)

With the rapid development of hydropower facility construction, the total dissolved gas (TDG) generated by dam discharge is seriously threatening the survival of fish and has become an ecological environmental issue of global concern. However, how TDG affects fish physiology and the underlying molecular mechanism remain poorly known. In this study, Acipenser dabryanus, an ancient living fossil that is a flagship species of the Yangtze River, was exposed to water supersaturated with TDG at a level of 116% for 48 h. A comprehensive analysis was performed to study the effect of TDG supersaturation stress on A. dabryanus, including histopathological, biochemical, transcriptomic and metabolomic analyses. The histopathological results showed that mucosal-associated lymphoid tissues were seriously damaged after TDG supersaturation stress. Plasma catalase levels increased significantly under TDG supersaturation stress, while superoxide dismutase levels decreased significantly. Transcriptomic analysis revealed 289 upregulated genes and 162 downregulated genes in gill tissue and 535 upregulated and 104 downregulated genes in liver tissue. Metabolomic analysis revealed 63 and 164 differentially abundant metabolites between the control group and TDG group in gill and liver, respectively. The majority of heat shock proteins and genes related to ubiquitin and various immune-related pathways were significantly upregulated by TDG supersaturation stress. Integrated transcriptomic and metabolomic analyses revealed the upregulation of amino acid metabolism and glycometabolism pathways under TDG supersaturation stress. Glycerophospholipid metabolism was increased which might be associated with maintaining cell membrane integrity. This is the first study revealing the underlying molecular mechanisms of effects of TDG supersaturation on fish. Our results suggested that acute TDG supersaturation stress could enhance immune and antioxidative functions and activate energy metabolic pathways as an adaptive mechanism in A. dabryanus.

Effect of total dissolved gas supersaturation on the survival of common carp (Cyprinus carpio) and silver carp (Hypophthalmichthys molitrix)

Flood discharge results in total dissolved gas (TDG) supersaturation downstream of a dam during the flood period. Fish suffer death from gas bubble disease (GBD) caused by TDG supersaturation. Nonetheless, current studies mainly attach importance to the survival of benthic fish affected by TDG supersaturation in the Yangtze River in China. Few studies have attempted to investigate the survival of pelagic fish influenced by TDG supersaturated water and compare the tolerance characteristics to TDG supersaturation between benthic and pelagic fish. To identify the survival of fish species that inhabit the various water layers affected by TDG supersaturation, silver carp (Hypophthalmichthys molitrix) (pelagic fish) and common carp (Cyprinus carpio) (benthic fish) were chosen to conduct an acute exposure experiment of four different TDG supersaturation levels (125%, 130%, 135% and 140%). The findings illustrated that the two fish species both exhibited evident aberrant behaviours of maladjustment in TDG supersaturated water. Obvious GBD symptoms were also found in the test fish. The survival probability of silver carp and common carp decreased with increasing levels of TDG supersaturation. The median survival time (ST₅₀ ) values of the silver carp exposed to four levels of TDG supersaturated water (125%, 130%, 135% and 140%) were 26.84, 7.96, 5.56 and 3.62 h, respectively, whereas the ST₅₀ values of common carp were 53.50, 26.00, 16.50 and 11.70 h, respectively. When compared with common carp, silver carp had a weaker tolerance to TDG-supersaturated water and were vulnerable to GBD. It shows that levels above 125% are not safe for common carp survival. In terms of the tolerance threshold value, silver carp merits further investigation because it showed lower tolerance to TDG than did common carp.

Effects of Total Dissolved Gas Supersaturation on the Survival of Juvenile Procypris rabaudi and Juvenile Myxocyprinus asiaticus at Varying Water Depth in a Natural River

Simple Summary

Total dissolved gas (TDG) supersaturation severely threatens the survival of fish downstream of a dam in the Yangtze River due to flood discharge. However, most studies have been executed in the laboratory. Few works have evaluated the effects of TDG supersaturation on fish in natural rivers during periods of flood discharge. In the present study, we investigated the survival of two rare species (Procypris rabaudi and Myxocyprinus asiaticus) when subjected to TDG-supersaturated water at varied water depths in the natural river during periods of flood discharge. The results of this study showed that deeper water depths can increase the tolerance of juvenile Procypris rabaudi to TDG supersaturation in natural rivers during periods of flood discharge while it cannot improve the survival of juvenile Myxocyprinus asiaticus. Juvenile Procypris rabaudi were more vulnerable to TDG supersaturation than juvenile Myxocyprinus asiaticus. The study results can promote the protection of juvenile Procypris rabaudi and juvenile Myxocyprinus asiaticus (or other rare species) and contribute to the improvement of reservoir operation practices in the Yangtze River.

Abstract

Total dissolved gas (TDG) supersaturation, which can be caused by flood discharge, results in gas bubble disease (GBD) in fish and threatens their survival downstream of dams. TDG supersaturation has become a serious environmental problem in the Yangtze River. Few studies have evaluated the effect of TDG supersaturation on fish in natural rivers during periods of flood discharge. To estimate fish tolerance to TDG supersaturation under natural conditions, juvenile Myxocyprinus asiaticus and juvenile Procypris rabaudi were exposed to TDG-supersaturated water for 96 h at various depths (0–0.3 m, 0.3–1.3 m, 1.3–2.3 m and 0–2.3 m) during periods of flood discharge of Dagangshan hydropower station. The results showed that juvenile Procypris rabaudi and juvenile Myxocyprinus asiaticus exhibited obvious GBD signs. An increase in exposure time decreased survival probability of the two species. Deeper water depths can increase the tolerance of juvenile Procypris rabaudi to TDG supersaturation in natural rivers during periods of flood discharge while it cannot improve the survival of juvenile Myxocyprinus asiaticus. Compared with juvenile Myxocyprinus asiaticus, juvenile Procypris rabaudi showed weaker tolerance of TDG supersaturation in shallow water, and juvenile Procypris rabaudi were more vulnerable to TDG supersaturation than juvenile Myxocyprinus asiaticus even if the TDG level (116%) was low.

Effect of Total Dissolved Gas Supersaturation on the Survival of Bighead Carp (Hypophthalmichthys Nobilis)

Simple Summary

Total dissolved gas (TDG) supersaturation severely threatens the survival of fish downstream of hydraulic structures in the Yangtze River due to flood discharge. However, existing findings mostly demonstrate the effect of TDG on the tolerance of benthic fish in China. Few studies have attached great importance to investigating the impact of TDG supersaturation on pelagic fish. Furthermore, varied flow of flood can lead to varied TDG levels in the spill season. Fish resided in the downstream of high dams may experience a period of chronic exposure at a low TDG level before the arrival of flood peak. However, rare achievement has reported that the survival situation of fish exposed to TDG supersaturated water with a high level after receiving chronic exposure. This study investigates the tolerance of bighead carp (Hypophthalmichthys nobilis) (pelagic fish) to TDG supersaturation and determine the effect of a high level of TDG supersaturation on its survival after chronic TDG exposure. The results showed that TDG led to apparent abnormal behaviours and gas bubble disease signs in bighead carp. The tolerance of bighead carp declined with increasing TDG levels. Compared with the large juvenile bighead carp, the small juvenile bighead carp are more sensitive to TDG. Furthermore, the results indicated that bighead carp subjected to acute exposure after long term chronic exposure are more vulnerable to TDG. The data from this study may provide valuable information related to protecting aquatic organism diversity and establishing water quality standards related to TDG supersaturation.

Abstract

To assess the effect of TDG on the survival of different sizes of pelagic fish, bighead carp (Hypophthalmichthys nobilis) were subjected to TDG supersaturated water at levels of 125, 130, 135, and 140%. The results showed that apparent abnormal behaviours and symptoms of gas bubble disease (GBD) were observed in bighead carp. The survival probability of large and small juvenile bighead carp declined with increasing TDG levels. The median survival time (ST₅₀) values of large juvenile bighead carp were 74.97 and 31.90 h at 130% and 140% TDG, respectively. While the ST₅₀ of small fish were 22.40 and 6.72 h at the same TDG levels. In comparison to the large juvenile bighead carp, the small juvenile bighead carp showed weaker tolerance to TDG supersaturated water. Furthermore, acute lethality experiments after chronic exposure to TDG were initiated to further investigate the effect of TDG on bighead carp. The juveniles were first subjected to 115% TDG supersaturated water for 96 h. After chronic exposure, live fish were immediately transferred to TDG supersaturated water at levels of 125, 130, 135, and 140%. The results demonstrated that no fish died under chronic exposure and few fish exhibited slight GBD symptoms. The ST₅₀ values for bighead carp subjected to acute exposure after chronic exposure were 61.23 and 23.50 h at 130 and 140%, respectively. Compared with the bighead carp subjected to acute exposure, bighead carp subjected to multiple exposures were more vulnerable to TDG.

Difference in biochemical markers in the gibel carp (Carassius auratus gibelio) upstream and downstream of the hydropower plant

However the physiological stress in aquatic organisms associated with hydropower plants (HPP) ecosystems has been previously investigated, no studies have so far assessed it on biochemical level. Therefore this study evaluated an oxidative stress and toxicity in the gibel carp Carassius auratus gibelio associated with a small-scale HPP in the West Ukraine. A battery of liver, brain and blood markers was evaluated individuals inhabiting upstream and downstream of the dam of the small-scale Kasperivtci HPP (KHPP; an installed capacity of 7.5 MW), and from a reference site. Number of alterations were noted in fish from the KHPP impoundment facility including signs of oxidative stress (a decrease in superoxide dismutase (SOD) activity and an increase in protein carbonyls) and cytotoxicity (an increase in micronucleated erythrocytes and caspase-3 activity). No changes in DNA fragmentation in hepatocytes or brain cholinesterase activity were detected. As demonstrated by the integral stress index, fish associated with downstream of the dam revealed the greatest alterations reflected by the combined oppression of antioxidant system (SOD, catalase) and pro-oxidants (thiobarbituric acid reactive substances and oxyradicals), low concentration of metallothioneins, but high cathepsin D activity (as markers of lysosomal dysfunction and autophagy) and increased vitellogenin concentration in males (indicating an endocrine disruption). The study highlights that fish inhabiting ecosystems associated with HPP, particularly downstream of the dam, may face additional stresses with long-term effects yet to be evaluated.

Lethal Effect of Total Dissolved Gas-Supersaturated Water with Suspended Sediment on River Sturgeon (Acipenser dabryanus)

High total dissolved gas (TDG) levels and excessive suspended sediment (SS) concentrations pose serious threats to fish survival during flood season. However, little information is available on the effects of TDG supersaturation with varying SS concentrations on fish. In this study, laboratory experiments were performed to investigate the effects of TDG supersaturation with varying SS concentrations on five-month-old river sturgeons (Acipenser dabryanus). The test fish were exposed to combinations of SS concentrations (0, 200, 600 and 1,000 mg/L) and TDG levels (125, 130, 135 and 140%), and their mortality and median lethal time (LT₅₀) were quantified. The fish showed abnormal behaviors (e.g., quick breathing, fast swimming and an agitated escape response) and symptoms of gas bubble disease (GBD). SS increased the mortality of river sturgeon exposed to TDG supersaturation. Furthermore, the LT₅₀ values at 125% TDG were 4.47, 3.11, 3.07 and 2.68 h for the different SS concentrations (0, 200, 600 and 1,000 mg/L, respectively), representing a significant decrease in LT₅₀ with increasing SS. However, at higher TDG levels (130–140%), there was no significant increase in LT₅₀ with increasing SS. Therefore, river sturgeon showed weak tolerance of TDG-supersaturated water with SS.

Effects of Total Dissolved Gas Supersaturation in Fish of Different Sizes and Species

Two endemic fish in the upper Yangtze River, the Rock Carp (Procypris rabaudi) and Prenant's Schizothoracin (Schizothorax prenanti), were used as research objects in this study to assess the effects of total dissolved gas (TDG) supersaturation on fish of varying sizes. Fish were exposed to TDG-supersaturated water at the levels of 145, 140, 135, 130, and 125%. The results showed that fish swam slowly, responded clumsily, and then exhibited spiral swimming performance after a period of exposure to TDG-supersaturated water. Fish exhibited exophthalmos, body swelling, gill bleeding, and caudal fin bleeding when they died in the TDG-supersaturated water. With the increase in TDG supersaturation, the tolerance capacity of fish to supersaturated TDG significantly reduced. At high supersaturation, the difference in survival time between species was not significant, while fish with smaller sizes showed greater tolerance capacity. At low supersaturation, the tolerance capacity of fish was mainly affected by species, and the influence of size was relatively small. With the decrease in TDG supersaturation, the catalase (CAT) activity first increased and then decreased. Rock Carp displayed significantly less activity than Prenant's Schizothoracin on exposure to TDG-supersaturated water. At high supersaturation levels, the CAT activity of Prenant's Schizothoracin of small size was greater than that of large Prenant's Schizothoracin. In contrast, small Prenant's Schizothoracin showed less CAT activity at low TDG levels than did large individuals.

Effect of total dissolved gas supersaturated water on early life of David's schizothoracin (Schizothorax davidi)

The effect of total dissolved gas (TDG) supersaturation on fish living downstream of dams is one of the main ecological risks of high dam construction. A strategy for mitigating the negative effects is needed urgently since many high dams are under construction in the upper reaches of the Yangtze River in China. Experiments on the hatching process of David's schizothoracin were carried out and the results show that the hatching rate decreased with increasing TDG levels, and that most eggs hatched within a very short time in the higher TDG saturation groups. By using a stereomicroscope, damages to the head, yolk sac, body, anus, etc. were found in larvae which hatched in TDG supersaturated water. Results show that the lesion rate increased with increasing TDG levels. Furthermore, 7-d-old David's schizothoracin were exposed to TDG supersaturated water levels of 100%, 105%, 110%, 115%, 120%, 125%, 130%, 135%, and 140% for testing their tolerance to TDG supersaturation. We found that the median lethal concentrations (LC50) for 13, 14, 20, 35, 52, 73, and 96 h exposure were 138%, 138%, 134%, 130%, 129%, 128%, and 126%, respectively. The median lethal times (LT50) were 7.49, 11.04, 19.25, and 35.38 h for exposure to water with TDG levels of 145%, 140%, 135%, and 130%, respectively.

Effects of total dissolved gas supersaturated water on lethality and catalase activity of Chinese sucker (Myxocyprinus asiaticus Bleeker)

Total dissolved gas (TDG) supersaturation caused by dam sluicing can result in gas bubble trauma (GBT) in fish and threaten their survival. In the present study, Chinese suckers (Myxocyprinus asiaticus Bleeker) were exposed to TDG supersaturated water at levels ranging from 120% to 145% for 48 h. The median lethal concentration (LC(50)) and the median lethal time (LT(50)) were determined to evaluate acute lethal effects on Chinese suckers. The results showed that the LC(50) values of 4, 6, 8, and 10 h were 142%, 137%, 135%, and 130%, respectively. The LT(50) values were 3.2, 4.7, 7.8, 9.2, and 43.4 h, respectively, when TDG supersaturated levels were 145%, 140%, 135%, 130%, and 125%. Furthermore, the biological responses in Chinese suckers were studied by assaying the catalase (CAT) activities in gills and muscles at the supersaturation level of 140% within LT(50). The CAT activities in the gills and muscle tissues exhibited a regularity of a decrease after an increase. CAT activities in the muscles were increased significantly at 3/5LT(50) (P<0.05) and then came back to the normal level. However, there were no significant differences between the treatment group (TDG level of 140%) and the control group (TDG level of 100%) on CAT activities in the gills before 3/5LT(50) (P>0.05), but the activities were significantly lower than the normal level at 4/5LT(50) and LT(50) (P<0.05).