Growth performance, oxidative stress, and non-specific immune responses in juvenile sablefish, Anoplopoma fimbria, by changes of water temperature and salinity

The tricarboxylic acid cycle is inhibited under acute stress from carbonate alkalinity in the gills of Eriocheir sinensis

Owing to population growth and environmental pollution, freshwater aquaculture has been rapidly shrinking in recent years. Aquaculture in saline-alkaline waters is a crucial strategy to meet the increasing demand for aquatic products. The Chinese mitten crab is an important economic food in China, but the molecular mechanism by which it tolerates carbonate alkalinity (CA) in water remains unclear. Here, we found that enzyme activities of the tricarboxylic acid (TCA) cycle in the gills, such as citrate synthase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and malate dehydrogenase, were markedly reduced under CA stress induced by 40 mM NaHCO3. Secondly, the TCA cycle in the gills is inhibited under acute CA stress, according to proteomic and metabolomic analyses. The expressions of six enzymes, namely aconitate hydratase, isocitrate dehydrogenase, 2-oxoglutarate dehydrogenase, dihydrolipoyl dehydrogenase, succinate-CoA ligase, and malate dehydrogenase, were downregulated, resulting in the accumulation of phosphoenolpyruvic acid, citric acid, cis-aconitate, and α-ketoglutaric acid. Finally, we testified that if the TCA cycle is disturbed by malonate, the survival rate increases in CA water. To our knowledge, this is the first study to show that the TCA cycle in the gills is inhibited under CA stress. Overall, the results provide new insights into the molecular mechanism of tolerance to saline-alkaline water in crabs, which helped us expand the area for freshwater aquaculture and comprehensively understand the physiological characteristics of crab migration.

Stevioside mitigates lead toxicity in thinlip mullet juveniles: Impacts on growth, metabolism, and immune function

This study investigates the impact of varying concentrations of stevioside in the presence of lead (Pb) exposure on multiple aspects of thinlip mullet (Liza ramada) juveniles. Over 60 days, a total of 540 juvenile L. ramada with an initial weight of 3.5 ± 0.13 g were evenly distributed into six groups, each consisting of three replicates. The experimental diet consisted of varying levels of stevioside (150, 250, 350, and 450 mg/kg diet), with a consistent concentration of lead (Pb) set at 100 µg/kg diet. Stevioside demonstrated a positive influence on growth parameters, with the 450 mg/kg +Pb treatment showing the highest values. Biochemical parameters remained stable, but lead-exposed fish without stevioside displayed signs of potential liver damage and metabolic issues. Stevioside supplementation, especially at higher doses (≥250 mg/kg), reversed these negative effects, restoring biochemical markers to healthy control levels. Lead exposure significantly suppressed antioxidant enzyme activities, but co-administration of stevioside exhibited a dose-dependent protective effect, with 250, 350, and 450 mg/kg groups showing activities comparable to the healthy control. Lead-exposed fish without stevioside demonstrated attenuation of the immune response, but stevioside supplementation reversed these effects, particularly at ≥250 mg/kg. Stev (≥250 mg/kg) reduced IL-1β and hepcidin expression, contrasting dose-dependent upregulation in lower dosages and lead-only group. Histological examinations of the intestine and liver supported these findings. In conclusion, stevioside, especially at 450 mg, positively impacted growth, biochemical parameters, antioxidant activity, immune response, and gene expression in L. ramada exposed to lead, suggesting its potential to mitigate lead toxicity in aquaculture. Additional research is warranted to investigate the long-term impacts of stevioside supplementation and its prospective implementation in aquaculture.

A Review on Biofloc System Technology, History, Types, and Future Economical Perceptions in Aquaculture

Given the scarcity of water and land resources, coupled with the competitive nature of aquaculture, the long-term viability of this industry will depend on strategies for vertical development. This involves enhancing production environments, increasing productivity, and advancing aquaculture technologies. The use of biofloc technology offers a potential solution to mitigate the adverse environmental impacts and the heavy reliance on fishmeal in the aquaculture sector. This method is designed to effectively assimilate inorganic nitrogen found in aquaculture wastewater, thereby enhancing water quality. Additionally, this process produces microbial protein, which can serve as a viable supplemental feed for aquatic animals. Furthermore, this technique has the potential to reduce the feed conversion ratio, thereby lowering overall production costs. This article provides an overview of the evolving field of biofloc system technology within aquaculture. In this study, we will examine the historical development and various types of biofloc systems, as well as the factors that influence their effectiveness. Finally, we will explore the economic potential of implementing biofloc systems in aquaculture.

ROS formation, mitochondrial potential and osmotic stability of the lamprey red blood cells: effect of adrenergic stimulation and hypoosmotic stress

Semi-anadromous animals experience salinity fluctuations during their life-span period. Alterations of environmental conditions induce stress response where catecholamines (CA) play a central role. Physiological stress and changes in external and internal osmolarity are frequently associated with increased production of reactive oxygen species (ROS). In this work, we studied the involvement of the cAMP/PKA pathway in mediating catecholamine-dependent effects on osmoregulatory responses, intracellular production of ROS, and mitochondrial membrane potential of the river lamprey (Lampetra fluviatilis, Linnaeus, 1758) red blood cells (RBCs). We also investigated the role of hypoosmotic shock in the process of ROS production and mitochondrial respiration of RBCs. For this, osmotic stability and the dynamics of the regulatory volume decrease (RVD) following hypoosmotic swelling, intracellular ROS levels, and changes in mitochondrial membrane potential were assessed in RBCs treated with epinephrine (Epi, 25 μM) and forskolin (Forsk, 20 μM). Epi and Forsk markedly reduced the osmotic stability of the lamprey RBCs whereas did not affect the dynamics of the RVD response in a hypoosmotic environment. Activation of PKA with Epi and Forsk increased ROS levels and decreased mitochondrial membrane potential of the lamprey RBCs. In contrast, upon hypoosmotic shock enhanced ROS production in RBCs was accompanied by increased mitochondrial membrane potential. Overall, a decrease in RBC osmotic stability and the enhancement of ROS formation induced by β-adrenergic stimulation raises concerns about stress-associated changes in RBC functions in agnathans. Increased ROS production in RBCs under hypoosmotic shock indicates that a decrease in blood osmolarity may be associated with oxidative damage of RBCs during lamprey migration.

Physiological Response of Spotted Seabass (Lateolabrax maculatus) to Different Dietary Available Phosphorus Levels and Water Temperature: Changes in Growth, Lipid Metabolism, Antioxidant Status and Intestinal Microbiota

A 10-week growth experiment was conducted to assess the physiological response of spotted seabass (Lateolabrax maculatus) raised at moderate (27 °C) and high temperatures (33 °C) to different dietary available phosphorus (P) levels. Five diets with available P levels of 0.35, 0.55, 0.71, 0.82 and 0.92% were formulated, respectively. A water temperature of 33 °C significantly decreased growth performance and feed utilization, and increased oxidative stress and lipid deposition of spotted seabass compared with 27 °C. A second-order polynomial regression analysis based on weight gain (WG) showed that the available P requirement of spotted seabass raised at 27 °C and 33 °C was 0.72% and 0.78%, respectively. The addition of 0.71-0.82% P to the diet improved the growth performance, feed utilization, and antioxidant capacity of spotted seabass and alleviated the excessive lipid deposition compared with the low-P diet (0.35% P). Moreover, the addition of 0.71-0.92% P to diets increased the diversity of intestinal microbiota and the relative abundance of Lactococcus lactis and decreased the relative abundance of Plesiomonas compared with the low-P diet. Thus, dietary supplementation with 0.71-0.82% P improved the growth performance, antioxidant capacity and microbial composition of spotted seabass, and alleviated the disturbance of lipid metabolism caused by high temperature or low-P diet.

Review of cadmium toxicity effects on fish: Oxidative stress and immune responses

Cadmium (Cd) in aquatic environments can cause environmental toxicity to fish and induce oxidative stress owing to an excessive production of reactive oxygen species in fish bodies. Fish have developed various antioxidant systems to protect themselves from reactive oxygen species; thus, a change in antioxidant responses in fish can be a criterion for evaluating oxidative stress resulting from Cd exposure. Because Cd exposure may be recognized as an exogenous substance by a fish body, it may lead to the stimulation or suppression of its immune system. Various immune responses can be assessed to evaluate Cd toxicity in fish. This review aimed to identify the impacts of Cd exposure on oxidative stress and immunotoxicity in fish as well as identify accurate indicators of Cd toxicity in aquatic ecosystems.

Captivating Colors, Crucial Roles: Astaxanthin's Antioxidant Impact on Fish Oxidative Stress and Reproductive Performance

Fish, constantly exposed to environmental stressors due to their aquatic habitat and high metabolic rates, are susceptible to oxidative stress. This review examines the interplay between oxidative stress and fish reproduction, emphasizing the potent antioxidant properties of astaxanthin. Our primary objective is to highlight astaxanthin's role in mitigating oxidative stress during critical reproductive stages, leading to improved gamete quality, ovary development, and hormone levels. We also explore its practical applications in aquaculture, including enhanced pigmentation and overall fish health. We conducted a comprehensive literature review, analyzing studies on astaxanthin's antioxidant properties and its impact on fish reproduction. Astaxanthin, a carotenoid pigment, effectively combats reactive oxygen species, inhibiting lipid peroxidation and maintaining membrane integrity. It significantly enhances reproductive success in fish and improves overall fish health in aquaculture settings. This review reveals astaxanthin's multifaceted benefits in fish health and reproduction, offering economic advantages in aquaculture. Future research should delve into species-specific responses, optimal dosages, and the long-term effects of astaxanthin supplementation to inform sustainable aquaculture strategies.

Effects of high NaHCO3 alkalinity on growth, tissue structure, digestive enzyme activity, and gut microflora of grass carp juvenile

With the gradual decrease in freshwater resources, the available space for freshwater aquaculture is diminishing. As a result, saline-alkaline water aquaculture has emerged as a crucial method to fulfill the increasing demand. This study investigates the impact of alkaline water on the growth performance, tissues (gill, liver, and kidney), digestive enzyme activity, and intestinal microbiology in grass carp (Ctenopharyngodon idella). The aquarium conditions were set with sodium bicarbonate (18 mmol/L (LAW), 32 mmol/L (HAW)) to simulate the alkaline water environment. A freshwater group was the control (FW). The experimental fish were cultured for 60 days. The findings revealed that NaHCO3 alkaline stress significantly reduced growth performance, caused alterations in the structural morphology of gill lamellae, liver, and kidney tissues, and led to decreased activity of intestinal trypsin and lipase amylase (P < 0.05). Analysis of 16S rRNA sequences demonstrated that alkalinity influenced the abundance of dominant bacterial phyla and genera. Proteobacteria showed a significant decrease under alkaline conditions, while Firmicutes exhibited a significant increase (P < 0.05). Furthermore, alkalinity conditions significantly reduced the abundance of bacteria involved in protein, amino acid, and carbohydrate metabolism, cell transport, cell decomposition, and environmental information processing. Conversely, the abundance of bacteria associated with lipid metabolism, energy metabolism, organic systems, and disease functional flora increased significantly under alkalinity conditions (P < 0.05). In conclusion, this comprehensive study indicates that alkalinity stress adversely affected the growth performance of juvenile grass carp, likely due to tissue damage, reduced activity of intestinal digestive enzymes, and alterations in intestinal microorganisms.

Effects of saline immersion on the physiological alterations of grass goldfish (Carassius auratus) during subsequent recovery in freshwater

The present work aims to evaluate the tolerance, osmoregulation, metabolism, and antioxidant ability of saline water immersed grass goldfish (Carassius auratus) during the recovery in freshwater. Grass goldfish (38.15 ± 5.48g) acclimated in freshwater were immersed by salinities (0‰, 20‰ and 30‰) for different time durations (10, 20, 30 and 60 min); and the physiological responses were measured during freshwater recovery. The blood osmolalities were not significantly different at any group fish, while whereas the decline of Na⁺ concentration and the ratio of Na⁺/Cl^- as well as the rise of Cl^- concentration was observed in saline treated fish. Soon after freshwater recovery, the transcription of NKA-α and NKA-β mRNA in gills of salinity 20 immersed fish elevated significantly and then decreased, whereas no obvious changes were detected in salinity 30 treated fish. Till 24h post freshwater recovery, gill Na+/K+-ATPase activities in saline treated fish were lower than control group except for the fish immersed by salinity 20 for 10-30 min. At 24h of recovery, cortisol levels in salinity 20 immersed fish were lower than salinity 30 treated fish, but remained higher than control. As for serum lactic acid, fish treated by salinity 20 for 10 or 20 min did not show any fluctuation. However, higher lactic acid contents were detected in all other five salinity treated groups during recovery. Generally, at 24 h of recovery, salinity 20 treated fish exhibited higher SOD and CAT activities than fish immersed by salinity 30. In summary, grass goldfish could survive by immersion in salinity 20 less than 60 min or salinity 30 less than 30min, even though immersion by salinity 20 could minimize the negative effects.

Toxic effects of microplastic (polyethylene) exposure: Bioaccumulation, hematological parameters and antioxidant responses in crucian carp, Carassius carassius

The purpose of this study was to evaluate the toxic effects of polyethylene microplastics (PE-MPs) by measuring the bioaccumulation, hematological parameters, and antioxidant responses in crucian carp (Carassius Carassius) exposed to waterborne 22-71 μm PE-MPs. C. carassius (mean weight, 24.0 ± 2.1 g; mean length, 13.1 ± 1.2 cm) were exposed to PE-MPs at concentration of 0, 4, 8, 16, 32, and 64 mg/L for 2 weeks. The accumulation of PE-MPs in each tissue of C. carassius was significantly increased in proportion to the PE-MPs concentration; the highest accumulation was observed in the intestine, followed by the gills and liver. Hematological parameters, plasma components and antioxidants responses were significantly affected by PE-MPs in a concentration-dependent manner. Exposure to ≥32 mg/L PE-MPs induced a significant decrease in red blood cells (RBCs), hemoglobin (Hb) content, and hematocrit values. However, exposure to ≥32 mg/L PE-MPs induced oxidative stress in the liver, gill, and intestine of C. carassius, thereby resulting in a significant increase in the levels of superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST) and a decrease in glutathione (GSH) levels. The effects of interaction between the PE-MPs and exposure periods showed no significant changes in bioaccumulation, hematological parameters, plasma components and antioxidant responses. These finding indicate that the exposure to ≥32 mg/L PE-MPs could cause a significant accumulation in specific tissues of C. carassius, resulting in changes in hematological parameters, plasma components, and antioxidant responses. However, the interaction between PE-MPs and exposure periods had no significant effects, thereby suggesting the lack of toxicological interactions between PE-MPs and exposure periods in C. carassius.

Oxidative stress responses in the respiratory tree and the body wall of sea cucumber Apostichopus japonicus (Selenka) to high temperature

Sea cucumber Apostichopus japonicas (Selenka) is one of the important aquaculture species distributed in northern China. In recent years, global warming caused frequent high temperature weather in summer in northern China, resulting in dramatic losses of the sea cucumber aquaculture industry. In the present study, we focused on the effect of oxidative stress in Apostichopus japonicus (Selenka) subjected to high temperature stress. Sea cumbers were exposed to the control (16 °C), and high temperature treatments (20 °C, 24 °C, and 28 °C) for 7 days. Then, reactive oxygen species (ROS) level, superoxide dismutase (SOD) activity, catalase (CAT) activity, peroxidase (POD) activity, reduced glutathione (GSH) content, malondialdehyde (MDA) content and 8-hydroxy-2'-deoxyguanosine (8-OHdG) level in the respiratory tree and body wall were detected, respectively. Results showed that 24 °C and 28 °C acute exposure induced the elevation of ROS level, SOD, CAT, POD activities, GSH content, MDA content and 8-OHdG level in the respiratory tree of sea cucumber. In contrast, no significant changes were observed for ROS and 8-OHdG levels in the body wall of sea cucumber, while the antioxidants including SOD, CAT, POD, and GSH decreased to some extent. Moreover, MDA content exhibited a noticeable increase in the body wall, similarly to that in the respiratory tree, indicating that high temperature could induce severe lipid peroxidation in two tissues. Considering the differences in various biomarkers measured in two tissues, respiratory tree might be more susceptible to the high temperature changes compared to the body wall. Our findings may help understand the oxidative stress response to high temperature in the respiratory tree and the body wall in A. japonicus.

Implications of Salinity and Acidic Environments on Fitness and Oxidative Stress Parameters in Early Developing Seahorses Hippocampus reidi

Water acidification affects aquatic species, both in natural environmental conditions and in ex situ rearing production systems. The chronic effects of acidic conditions (pH 6.5 vs. pH 8.0) in seahorses (Hippocampus spp.) are not well known, especially when coupled with salinity interaction. This study investigated the implications of pH on the growth and oxidative stress in the seahorse Hippocampus reidi (Ginsburg, 1933), one of the most important seahorse species in the ornamental trade. Two trials were carried out in juveniles (0-21 and 21-50 DAR-days after the male's pouch release) reared under acid (6.5) and control (8.0) pH, both in brackish water (BW-salinity 11) and seawater (SW-salinity 33). In the first trial (0-21 DAR), there was no effect of pH on the growth of seahorses reared in SW, but the survival rate was higher for juveniles raised in SW at pH 6.5. However, the growth and survival of juveniles reared in BW were impaired at pH 6.5. Compared to SW conditions, the levels of superoxide dismutase and DT-diaphorase, as well as the oxidative stress index, increased for juveniles reared in BW. In the second trial, seahorse juveniles were reared in SW at pH 8.0, and subsequently kept for four weeks (from 21 to 50 DAR) at pH 6.5 and 8.0. The final survival rates and condition index were similar in both treatments. However, the growth under acidic conditions was higher than at pH 8.0. In conclusion, this study highlights that survival, growth, and oxidative status condition was enhanced in seahorse juveniles reared in SW under acidic conditions (pH = 6.5). The concurrent conditions of acidic pH (6.5) and BW should be avoided due to harmful effects on the fitness and development of seahorse juveniles.

Nuclear and Morphological Alterations in Erythrocytes, Antioxidant Enzymes, and Genetic Disparities Induced by Brackish Water in Mrigal Carp (Cirrhinus mrigala)

Salinization of aquatic ecosystem, abrupt climate change, and anthropogenic activities cause adverse impact on agricultural land/soil as well as the aquaculture industry. This experimental study was designed to evaluate different biomarkers of oxidative stress, antioxidant enzymes, and genotoxic potential of diverse salinities of brackish water on freshwater fish. A total of 84 fresh water mrigal carp (Cirrhinus mrigala) were randomly segregated and maintained in four groups (T0, T1, T2, and T3) in a glass aquarium under similar laboratory conditions at various salinity levels (0, 3, 5, and 7 parts per thousand) to determine the pathological influence of brackish water. All the fish in groups T1, T2, and T3 were exposed to various salinity levels of brackish water for a period of 90 days while the fish of group T0 served as the control group. The experimental fish reared in different groups T1, T2, and T3 displayed various physical and behavioral ailments. The results revealed significantly augmented quantity of different oxidative stress indicators including reactive oxygen species (ROS) and thiobarbituric acid reactive substance (TBARS) in different visceral tissues (kidneys, liver, and gills) of exposed fish. Different antioxidant enzymes such as reduced glutathione (GSH), peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) along with total proteins were remarkably reduced in the kidneys, gills, and liver tissues. Results showed significantly increased values of different nuclear abnormalities (erythrocyte with micronucleus, erythrocyte with condensed nucleus, and erythrocyte with lobed nucleus) and morphological changes (pear shaped erythrocyte, spindle-shaped erythrocytes, and spherocyte) in red blood cells of experimental fish. The results on genotoxic effects exhibited significantly increased DNA damage in isolated cells of liver, kidneys, and gills of exposed fish. The findings of our experimental research suggested that brackish water causes adverse toxicological impacts on different visceral tissues of fresh water fish at higher salinity level through disruption and disorder of physiological and biochemical markers.

Effects of salinity stress on antioxidant status and inflammatory responses in females of a "Near Threatened" economically important fish species Notopterus chitala: a mechanistic approach

In the present study, acute stress responses of adult female Notopterus chitala were scrutinized by antioxidant status and inflammation reaction in the gill and liver at five different salinity exposures (0, 3, 6, 9, 12 ppt). Oxidative defense was assessed by determining superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase, and glutathione reductase activities, while malondialdehyde (MDA), glutathione, and xanthine oxidase levels were determined as indicators of oxidative load. Pro-inflammatory cytokines (IL-1β, IL-6, IL-10, and TNFα) and caspase 1 levels were also analyzed. Expression levels of transcription factors (NRF2 and NF-κB) and molecular chaperons (HSF, HSP70, and HSP90) were estimated to evaluate their relative contribution to overcome salinity stress. MDA showed a significant (P < 0.05) increase (gill, + 25.35-90.14%; liver, + 23.88-80.59%) with salinity; SOD (+ 13.72-45.09%) and CAT (+ 12.73-33.96%) exhibited a sharp increase until 9 ppt, followed by a decrease at the highest salinity (12 ppt) (gill, - 3.92%; liver, - 2.18%). Levels of cytokines were observed to increase (+ 52.8-127.42%) in a parallel pattern with increased salinity. HSP70 and HSP90 expressions were higher in gill tissues than those in liver tissues. NRF2 played pivotal role in reducing salinity-induced oxidative load in both the liver and gills. Serum cortisol and carbonic anhydrase were measured and noted to be significantly (P < 0.05) upregulated in salinity stressed groups. Gill Na⁺-K⁺-ATPase activity decreased significantly (P < 0.05) in fish exposed to 6, 9, and 12 ppt compared to control. Present study suggests that a hyperosmotic environment induces acute oxidative stress and inflammation, which in turn causes cellular death and impairs tissue functions in freshwater fish species such as Notopterus chitala.

Blood biochemical variables, antioxidative status, and histological features of intestinal, gill, and liver tissues of African catfish (Clarias gariepinus) exposed to high salinity and high-temperature stress

African catfish is a freshwater species with a high ability to resist brackish water conditions, but heat stress may impair the health status of fish. Thus, the impact of varying levels of water salinity (0, 4, 8, and 12 ppt) was investigated on the growth performance, survival rate, and blood biochemistry of African catfish (average weight: 180.58 ± 2.8 g and average length: 38 ± 1.2 cm) for 4 weeks; then, fish were stressed with high temperature (32 °C) for 72 h. The growth performance and survival rate were markedly higher in fish reared in 0, 4, and 8 ppt than fish in 12 ppt (p < 0.05). Before heat stress, the superoxide dismutase (SOD), catalase (CAT), glutathione (GSH) activities, and malondialdehyde (MDA) levels were markedly increased in fish stressed with 12-ppt salinity (p < 0.05). After heat stress, all groups showed a marked increased SOD, CAT, GSH, and MDA levels than fish before heat stress in the same manner (p < 0.05). Furthermore, fish in the 12 ppt group showed severe intestinal, gill, and liver histological features. The levels of blood glucose and cortisol were markedly increased in fish exposed with 8 and 12 ppt than 0 ppt gradually either before or after heat stress (p < 0.05). The highest values of ALT, AST, urea, creatinine, and the lowest total protein, albumin, and globulin were observed in fish reared in 12 ppt. Significant salinity and heat stress interactions were seen on the ALT, AST, urea, creatinine, total protein, albumin, and globulin values (p < 0.05). The integrated multi-biomarker response (IBR) results showed marked differences among the groups and increased gradually before and after heat stress, with the highest IBR in 12 ppt. In conclusion, growing African catfish in high salinity (12 ppt) hampered the growth performance and health status while the heat stress improved the antioxidative status vis-a-vis increased lipid peroxidation along with higher stress-related markers in expressed both blood and tissue.

Integrated application of multi-omics approach and biochemical assays provides insights into physiological responses to saline-alkaline stress in the gills of crucian carp (Carassius auratus)

Given the decline of freshwater resources in recent years, the accessible space for freshwater aquaculture is rapidly shrinking, and aquaculture in saline-alkaline water has become a critical approach to meet the rising demand. However, the molecular mechanism behind the adverse effects of saline-alkaline water on fish and the regulatory mechanism in fish tolerance remains unclear. Here, adult crucian carp (Carassius auratus) were exposed to 60 mmol/L NaHCO₃ for 30 days. It was observed that long-term carbonate alkalinity (CA) exposure not only caused gill oxidative stress but also changed the levels of several physiological parameters associated with ammonia transport, including blood ammonia, urea nitrogen (BUN), glutamine (Gln), and glutamine synthetase (GS). According to the metabolomics study, differential metabolites (DMs) engaged in various metabolic pathways, such as glycerophospholipid metabolism, sphingolipid metabolism, and arachidonic acid metabolism. In addition, transcriptomics data showed that differentially expressed genes (DEGs) were closely related to ammonia transport, apoptosis, and immunological response. In general, comprehensive multi-omics and biochemical analysis revealed that crucian carp might adopt Rh glycoprotein as a carrier to mediate ammonia transport and increase glutamine and urea synthesis under long-term high saline-alkaline stress to mitigate the adverse effects of blocked ammonia excretion. Simultaneously, saline-alkaline stress caused the destruction of the antioxidant system and the disorder of lipid metabolism in the crucian carp gills, which induced apoptosis and immunological response. To our knowledge, this is the first study to investigate fish's molecular and metabolic mechanisms under saline-alkaline stress using integrated metabolomics, transcriptomics, and biochemical assays. Overall, the results of this study provided new insights into the molecular mechanism behind the adverse effects of saline-alkaline water on fish and the regulatory mechanism in fish tolerance.

The antioxidant responses of gills, intestines and livers and blood immunity of common carp (Cyprinus carpio) exposed to salinity and temperature stressors

Aquaculture activity is affected by various environmental factors, including water salinity and high temperatures. The present study investigated the impact of using varying water salinity (0, 5, 10, 15 and 20 ppt) on the growth behavior, immune responses and antioxidative responses of common carp. Fish were raised under optimal conditions except for water salinity for 8 weeks; fish were then subjected to high-temperature stress (32 °C) for 48 h. The results indicated a reduced final weight (FBW), weight gain (WG), specific growth rate (SGR), condition factor (CF), feed intake and feed efficiency ratio (FER) in common carp reared in 15 and 20 ppt (p < 0.05). The lowest FBW, WG, SGR, CF, feed intake and FER values were observed in fish reared in 20 ppt water salinity (p < 0.05). In gills, the superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were markedly decreased, but malondialdehyde (MDA) levels increased in fish challenged with 15 and 20 ppt before they were subjected to heat stress (p < 0.05). After heat stress, the SOD, CAT and GPx were decreased, and the MDA increased in fish reared in varying salinity levels (p < 0.05). Before heat stress, the intestinal SOD, CAT and GPx markers were decreased by 15 and 20 ppt, while the MDA level was increased by 15 and 20 ppt (p < 0.05). Generally, heat stress lowered the SOD, CAT and GPx activity in the intestines and liver tissues but increased MDA levels in common carp stressed by varying salinity levels (p < 0.05). The most decreased lysozyme activity, SOD, CAT and GPx and increased MDA levels were observed in common carp exposed to 20 ppt before and after heat stress (p < 0.05). After heat stress, fish exposed to 15 and 20 ppt had lower NBT than the remaining groups, and fish exposed to 20 ppt had the lowest values (p < 0.05). Overall, the heat stress markedly suppressed the antioxidant and immune responses of common carp reared in hypersalinity conditions.

Acute ammonia exposure combined with heat stress impaired the histological features of gills and liver tissues and the expression responses of immune and antioxidative related genes in Nile tilapia

Ammonia exposure can be considered more stressful for aquatic animals when it coincides with high temperature. This study was conducted to detect the effects of ammonia exposure and heat stress and their interactions on the histological features of gills and liver tissues and the expression responses of immune and antioxidative related genes in Nile tilapia. Thus, 180 fish were divided into four groups (triplicates), where the first and third groups were kept in clean water without total ammonium nitrogen (TAN) exposure. At the same time, the second and fourth groups were exposed to 5 mg TAN/L. After seven days, the water temperature was raised in the third (without ammonia toxicity) and fourth (exposed with 5 mg TAN/L) groups up to 32 °C and kept under these conditions for 24 h. While the first (without ammonia toxicity) and second (exposed with 5 mg TAN/L) groups were kept under optimum water temperature (27.28 °C) then gills and liver tissues were dissected. Marked upregulation of keap1 was seen in the gills of fish exposed to ammonia/heat stress. The expression of mRNA levels for nrf2, nqo-1, cat, and gpx genes were downregulated in all stressed groups, with the lowest was recorded in the ammonia/heat stress group. The transcription of ho-1 was upregulated in the ammonia and heat stress groups while downregulated in the ammonia/heat stress group. The transcription of the complement C3 gene was downregulated in the livers of heat stress and ammonia/heat stress groups, while the lysozyme gene was downregulated in the ammonia/heat stress group. The mRNA expression levels of nf-κB, il-1β, and tnf-α genes were higher in the ammonia group than in the heat stress group. The highest transcription level of nf-κB, il-1β, tnf-α, il-8, and hsp70 genes and the lowest C3 and lysozyme genes were observed in fish exposed to ammonia/heat stress. The co-exposure to ammonia with heat stress triggered degeneration of primary and secondary gill filaments with telangiectasia and vascular congestion of secondary epithelium while, the liver showed hepatic vascular congestion and visible necrotic changes with nuclear pyknosis. In conclusion, the combined exposure of ammonia and heat stress induced oxidative stress, immunosuppression, and inflammation in Nile tilapia.

Effects of salinity on gills' chloride cells, stress indices, and gene expression of Asian seabass (Lates calcarifer, Bloch, 1790)

A 2-week research was carried out to assess water salinity (WS) effects including 0, 15, 35, and 50‰ on osmoregulatory mechanisms and stress indices in Asian sea bass (34.4 g) juveniles. Except for fish reared at 50‰, in the other treatments, it gradually decreased to the prescribed WS during a 10-day period (- 5‰ a day). After a 10-day acclimation period, fish were reared at the prescribed WS for 2 weeks. Fish reared at 15 and 35‰ had higher chloride cell (CC) counts in the interlamellar region. The number of CC in the interlamellar region elevated with increment of WS up to 35‰, but they were pronouncedly reduced in 50‰ group. The diameter of CC in the interlamellar region was not affected by WS. The smallest nucleus diameter of CC in the interlamellar region was observed in fish reared at 15‰ (P < 0.05). The largest and the smallest amounts of serum aspartate aminotransferase were observed in fish reared at freshwater and 15‰, respectively. Fish reared at 35‰ had the highest serum sodium and potassium contents. Serum chloride content and total osmolality increased with increment of WS (P < 0.05). Serum cortisol and glucose contents gradually increased with elevation of WS up to 35‰; then, their contents remarkably decreased. The relative expression of insulin like growth factor-1 in the liver of fish reared at 35‰ was strikingly higher than that in the other groups. The relative expression of HSP70 gene in fresh water group was pronouncedly elevated compared to other treatments. The relative expression of interleukin-1β in 15 and 35‰ groups was higher than that in the other groups; however, the relative expression of lysozyme gene in the liver of fish reared at fresh water was pronouncedly lower than that in the other treatments. The results of this study suggested rearing L. calcarifer at 15‰ closer to the isosmotic point and better provide its welfare.

Salinity affects growth performance, physiology, immune responses and temperature resistance in striped catfish (Pangasianodon hypophthalmus) during its early life stages

In this study, striped catfish larvae were gradually exposed to the increase of different salinities, and then they reached the levels of 0, 5, 10, 15, and 20 psu after 10 days, followed by heat shock at 39 °C to determine stress tolerance. After the 10-day experiment, the survival rate of fish exposed to the 20 psu treatment was only 28.6 ± 4%, significantly lower than that of the other treatments. The results showed that the osmolality of the whole-body (WB) homogenate was gradually and significantly increased with salinity elevation, except in fish exposed to freshwater and 5 psu treatments, while there were no significant changes in WB Na⁺/K⁺-ATPase activity. Digestive enzymatic activities, i.e., pepsin, α-amylase, alkaline phosphatase, and leucine alanine peptidase (leu-ala) generally increased with salinity, but not aminopeptidase and trypsin. Lysozyme and peroxidase activities increased in fish larvae exposed to 15 and 20 psu. These increases proportionally improved growth performance, with the lowest and the highest final weights observed in fish reared at 0 psu (0.08 ± 0.03 g/larvae) and 20 psu (0.11 ± 0.02 g/larvae), respectively, although the average growth recorded at 20 psu could be biased by the high mortality in this group. Occurrence of skeleton deformities, such as in caudal vertebrae and branchiostegal rays, was significantly higher in fish exposed to the higher osmotic conditions (15.0 ± 1.2% and 10.3 ± 2.1% respectively at 0 psu vs. 31.0 ± 2.9% and 49.0 ± 5.6%, respectively at 15 psu). After the 12.5-h heat shock, survival rates significantly differed between treatments with the highest survival observed in fish submitted to 5 psu (68.9%), followed by those exposed to 0 (27%) and 10 (20%) while all fish died at 15 psu. These findings suggest that the striped catfish larvae could be reared in salinity up to 5 to 10 psu with a higher survival and tolerance to thermal stress when compared to fish maintained in freshwater.

Characterization of p53 From the Marine Crab Portunus trituberculatus and Its Functions Under Low Salinity Conditions

Portunus trituberculatus, or the swimming crab, is tolerant of reduced salinity; however, the molecular mechanism of this tolerance is not clear. Cells can be damaged by hyperosmotic salinity. The protein p53, sometimes referred to as “the guardian of the genome,” displays versatile and important functions under changing environmental conditions. Herein, the P. trituberculatus p53 gene (designated as Ptp53) was cloned and studied. The full-length Ptp53 cDNA comprised 1,544bp, with a 1,314bp open reading frame, which encodes a putative polypeptide of 437 amino acids. Quantitative real-time reverse transcription PCR assays revealed ubiquitous expression of Ptp53 in all tissues examined, with the gills showing the highest expression level. Extensive apoptosis was detected under low salinity conditions using terminal deoxynucleotidyl transferase nick-end-labeling staining. Oxidative stress was induced under low salinity conditions, consequently leading to apoptosis. Low salinity stress caused significant upregulation of Ptp53 mRNA and protein levels in the gills. Moreover, compared with that in the control group, the mortality of Ptp53-silenced crabs under low salinity stress was enhanced significantly. Taken together, our findings suggest that Ptp53, via regulation of apoptosis and antioxidant defense, played important functions in the low salinity stress response of the swimming crab.

Gill physiological and transcriptomic response of the threatened freshwater mussel Solenaia oleivora to salinity shift

Solenaia oleivora, a freshwater shellfish endemic to China, is becoming one of the most threatened freshwater mussels owing to water pollution, habitat fragmentation, and overfishing. Hence, exploring its response to different environmental factors is important for its conservation. In this work, we investigated the physiological and transcriptomic response of S. oleivora to increased salinity. We found that increased salinity caused the death of S. oleivora. High salinity caused shrinking and deformation of gill filaments, reduced gill cilia, and induced cell apoptosis in gills. The activities of superoxide dismutase (SOD), catalase (CAT), acid phosphatase (ACP), alkaline phosphatase (AKP), as well as glutathione (GSH) content were increased at the beginning of salinity stress (3-12 h), while SOD and ACP activities decreased at 48 h. Transcriptome data revealed that high salinity stress (48 h) induced 766 differentially expressed genes (DEGs). Among these DEGs, the majority of the stress response and ion transport-related genes were up-regulated, while most of the immune-related genes were down-regulated. In conclusion, these findings suggest that the antioxidant and immune functions of S. oleivora can be inhibited by high salinity, which may be one of the main reasons for its low survival rate under conditions of increasing salinity.

Culture salinity modulates Nrf2 antioxidant signaling pathway and immune response of juvenile Genetically Improved Farmed Tilapia (GIFT) (Oreochromis niloticus) under different dietary protein levels

This study aimed to evaluate that dietary protein levels and culture salinity levels affect the health status of juvenile genetically improved farmed tilapia (GIFT, Oreochromis niloticus). Graded protein levels of six diets were prepared, ranging from 18.20% to 49.49% (dry basis), and were used in cultured GIFT at two salinity levels (0‰ and 8‰) for 8 weeks. The results suggested that appropriate protein levels reduced pro-inflammatory gene expressions in the intestine including interleukin 1β (IL-1β), interleukin 8 (IL-8) and tumour necrosis factor-α (TNF-α) mRNA levels at two salinity levels (P < 0.05). 8‰ salinity significantly decreased the expression levels of IL-1β, TNF-α and nuclear factor-kappa B (NF-κB) (P < 0.05). The anti-inflammatory factor interleukin 10 (IL-10) was significantly increased by 36.42% protein level (P < 0.05). Regarding antioxidant capacity, appropriate protein levels and 8‰ salinity significantly improved the antioxidant capacity of fish by regulating the activities of intestinal total superoxide dismutase (T-SOD), glutathione peroxidase (GPx), and the levels of glutathione (GSH) and malondialdehyde (MDA). Furthermore, appropriate protein levels and 8‰ salinity also significantly enhanced the antioxidant gene expressions associated with the Nrf2/keap1 signaling pathway by regulating the expression levels of heme oxygenase-1 (HO-1), GPx, catalase (CAT) and superoxide dismutase (SOD). According to GPx activities and the mRNA levels of IL-10, the optimum dietary protein levels for GIFT juveniles were 31.12%-32.18% (0‰) and 34.25-35.38% (8‰) based on second-degree polynomial regression analysis. The present study found that appropriate protein levels and 8‰ culture salinity are critical in maintaining the health of GIFT juveniles by improving antioxidant and immune capacity.

Influence of salinity on physiological development and zinc toxicity in the marine medaka Oryzias melastigma

To determine whether the marine medaka Oryzias melastigma is a suitable model organism for evaluating the effects of environmental chemicals on marine teleosts, we examined the effect of salinity on physiological development and zinc toxicity. Growth as measured by total body length was significantly lower in fresh water compared to brackish water. Reproductive success was also significantly reduced in fresh water, although we observed cells in the pituitary producing gonadotropins such as Gpa (common glycoprotein hormone α), Fshb (follicle stimulating hormone β), and Lhb (luteinizing hormone β) at all salinities. These results indicate that O. melastigma is adaptable to various salinities from fresh to seawater, and brackish water is best for physiological processes including growth performance and reproduction. When zinc was dissolved in saltwater, a white precipitate formed immediately, and the dissolved concentration decreased in the supernatant and increased at precipitate. We performed zinc toxicity tests on early life stage and adult stage in fresh water, brackish water, and seawater. Among adults, the lowest observed effect concentration for mortality in freshwater (15.3 mg/L) was lower than in brackish water (>48 mg/L) or seawater (>48 mg/L). Similarly, among embryos and larvae, the lowest observed effect concentration for mortality in freshwater (4.8 mg/L) was lower than in brackish water (48 mg/L) or seawater (48 mg/L). These results highlight the importance of using marine organisms to evaluate the ecological effects of marine pollutants.

How does elevated water temperature affect fish brain? (A neurophysiological and experimental study: Assessment of brain derived neurotrophic factor, cFOS, apoptotic genes, heat shock genes, ER-stress genes and oxidative stress genes)

Water temperature is one of the most important environmental factors affecting the growth and survival of fish. Increased water temperature became a global problem and it is estimated that there will be an increase in water temperature due to global climate change. The physiological mechanism for the effects of high water temperature on the fish brain is not fully known. In the present study, fish were exposed to different temperatures (10 °C/15 °C/20 °C/25°) and brain tissues were sampled 2 h-4h-6h-8h per hour respectively and then we investigated transcriptional changes of BDNF, cFOS, apoptotic genes (caspase 3, Bax, Bcl2), heat shock genes (Hsp70 and Hsp 90) ER-Stress genes (grp78, atf6, and ire1) and oxidative stress genes (CAT, SOD, and GPx) and also immunoflourescence changes of BDNF and cFOSin rainbow trout brain. The results indicated that high temperature stress lead to physiological changes in the fish brain by causing a decrease in mRNA expression levels of CAT, SOD, GPx and Bcl2 and by causing an increase in mRNA expression of BDNF, cFOS, apoptotic genes (caspase 3, Bax), heat shock genes (Hsp70 and Hsp 90) ER-Stress genes (grp78, atf6, and ire1). This study will provide important information to elucidate the physiological mechanisms related to the effects of high water temperature on the fish brain.

Toxic effects on bioaccumulation, hematological parameters, oxidative stress, immune responses and neurotoxicity in fish exposed to microplastics: A review

Exposure to microplastics (MP) in aquatic environment leads to bioaccumulation in fish, with MP size being a major factor in determining the accumulation profile. MPs absorbed into the fish body enter the circulatory system and affect hematological properties, changing the blood physiology. MPs also induce an imbalance in reactive oxygen species (ROS) production and antioxidant capacity, causing oxidative damage. In addition, MPs impact immune responses due to physical and chemical toxicity, and cause neurotoxicity, altering AchE activity. Here, the toxic effects of MPs in fish through various indicators were examined, including bioaccumulation, hematological parameters, antioxidant responses, immune responses, and neurotoxicity in relation to MP exposure, facilitating the identification of biomarkers of MP toxicity following exposure of fish.

High concentrations of environmental ammonia induced changes in large-scale loach (Paramisgurnus dabryanus) immunity

High concentrations of environmental ammonia can cause reduced immunity and death in fish, causing enormous economic losses. Air-breathing fish usually have a high ammonia tolerance and are very suitable for high-density fish farming. However, research on the effects of environmental ammonia on air-breathing fish immunity is lacking. Therefore, this study investigated the effects of environmental ammonia on the immunity of large-scale loach (Paramisgurnus dabryanus) by exposing fish to 30 mmol/L NH4Cl solution and subsequently analyzing the changes in serum and liver immune indicators, including total protein, albumin, globulin, immunoglobulin (Ig) M, lysozyme, complement component (C) 3 and C4, heat shock protein (HSP) 70, HSP90, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and IL-12. Results revealed that ammonia exposure significantly affected the total protein, albumin, globulin, IgM, complement C3 and C4, HSP70, HSP90, and inflammatory cytokine contents in the body, indicating that ammonia exposure induced a significant immune response and lowered bodily immunity. However, most of the immune indicators significantly decreased in the later stages of the experiment, suggesting a weakened immune response, which may be due to the species-specific ammonia detoxification ability of large-scale loach that reduces ammonia toxicity in the body.

Inflammatory responses associated with hyposaline stress in gill epithelial cells of the spotted scat Scatophagus argus

The molecular processes of immune responses in mucosal tissues such as fish gills under environmental stress are poorly understood. In the present study, pro-inflammatory response under hyposaline stress and its regulation by cortisol/corticosteroid receptors (CRs) in gill epithelial cells of the spotted scat Scatophagus argus were analyzed. The fish were transferred to freshwater for 6 days (144 h) of acclimation. Following freshwater exposure, the cortisol concentration increased transiently before returning to the control level over time. mRNA expression of pro-inflammatory cytokines (TNF-a, IL-1b and IL-6) was stimulated by cortisol through CR signals at early stages of acclimation, but hyposaline stress inhibited their levels by the end of the experimental period. The transcriptional profile of anti-inflammatory cytokine IL-10 was quite different from these pro-inflammatory cytokines, and its value fluctuated within a narrow range during the experimental period. Full-length cDNAs of mineralocorticoid receptor (MR) and glucocorticoid receptor 1 (GR1) (different kinds of CRs) were cloned from the gills. Our results showed that MR and GR displayed mutually antagonistic effects during hyposaline stress. MR responded quickly at early stages, and its expression decreased with the drop of cortisol concentration. By contrast, GR expression was maintained at high levels after the acclimation of freshwater exposure. The tight coordination of GR and MR helps to shape the effects of stress on the immune system, which in turn, regulates the stress response. Our results confirm the interaction between endocrine and cytokine messengers and a clear difference in the sensitivity of GR and MR during the hyposaline challenge in gill epithelial cells of the spotted scat Scatophagus argus.

Garlic (Allium sativum) and Fu-ling (Poria cocos) mitigate lead toxicity by improving antioxidant defense mechanisms and chelating ability in the liver of grass carp (Ctenopharyngodon idella)

The heavy metal lead (Pb) is a contaminant widely distributed in the food chain. In this study, eight weeks of feeding containing Garlic (Allium sativum) or Fu-ling (Poria cocos) or both, markedly increased the growth index, enzyme activity, and serum index and significantly decreased muscle Pb level in grass carp (Ctenopharyngodon idella). Upon Pb exposure, the feeding Garlic or Fu-ling or both possessed the similar effects on improving the function of the antioxidant system and chelating ability. Further, the gene expressions of metal binding proteins (TF and MT-2) in the liver of the three experimental groups were significantly higher than those of the control group, which were all highly up-regulated after Pb exposure. At the same time, the activities of antioxidant enzymes (SOD and CAT) and the content of non-enzymatic substance (GSH) in the liver of the Garlic group, Fu-ling group and mixed group were stable compared to the control group after Pb exposure. Moreover, the reduction of Pb toxicity was manifested by the decrease of Pb content in the muscle, and the stable expression of heat stress proteins (HSP30 and HSP60) and immune-related genes (TNF-α and IL-1β). Taken together, the study preliminarily shows that the Garlic and Fu-ling play a role in mitigating the toxicity of Pb in grass carp.

Acute toxicity and sublethal effects of sodium laureth sulfate on oxidative stress enzymes in benthic oligochaete worm, Tubifex tubifex

The present study was performed to determine the acute toxicity of sodium laureth sulfate (SLES) and its sublethal effects on oxidative stress enzymes in benthic oligochaete worm Tubifex tubifex. The results showed that 96 h median lethal concentration (LC₅₀) value of SLES for Tubifex tubifex is 21.68 mg/l. Moreover exposed worms showed abnormal behaviours including incremented erratic movement, mucus secretion, and decreased clumping tendency at acute level. Percentage of autotomy additionally increased significantly (P < 0.05) with the increasing dose of toxicant at 96 h exposure. Sublethal concentrations of SLES (10% and 30% of 96 h LC₅₀ value) caused paramount alterations in the oxidative stress enzymes. Superoxide dismutase (SOD), reduced glutathione (GSH), glutathione S-transferase (GST), and glutathione peroxidase (GPx) exhibited a striking initiatory increment followed by a resulting descending pattern. Moreover, during exposure times, catalase (CAT) activity and malondialdehyde (MDA) level increased markedly with incrementing concentrations of SLES. However, the effects of sodium laureth sulfate on Tubifex tubifex were characterized and portrayed by the development of a correlation matrix and an integrated biomarker response (IBR) assessment. These results indicate that exposure to this anionic surfactant alters the survivability and behavioral response at acute level and modifies changes in oxidative stress enzymes at sublethal level in Tubifex tubifex.

Salinity-mediated changes in hematological parameters, stress, antioxidant responses, and acetylcholinesterase of juvenile olive flounders (Paralichthys olivaceus)

The purpose of this study was to confirm the limit of salinity tolerance in juvenile olive flounders (Paralichthys olivaceus) by changes in blood parameters, AChE, antioxidant and stress responses. The P. olivaceus (mean weight 38.8 ± 4.2 g and mean length 16.4 ± 1.2 cm) were exposed to different concentrations of salinity (seawater, 16, 8, 4, 2, and 0 psu) for 2 weeks. Plasma osmotic pressure was significantly decreased in the P. olivaceus at 0 psu. Hematological parameters such as hematocrit and hemoglobin were significantly decreased in the P. olivaceus at low salinity. Plasma components also changed significantly in the low salinity environment. As a stress indicator, cortisol was significantly increased at low salinity. SOD and GST antioxidant responses, were significantly increased. GSH level in the liver was significantly increased, whereas a significant decrease was observed in the gill GSH level. AChE was significantly increased in P. olivaceus at low salinity. The results of this study indicate that exposure to salinities lower than 8 psu leads to changes in hematological parameters, neurotransmitter, antioxidant and stress responses of P. olivaceus.

A Multi-Biomarker Approach in European Sea Bass Exposed to Dynamic Temperature Changes under Dietary Supplementation with Origanum vulgare Essential Oil

A feeding trial for 150 days was carried out to evaluate the cross-effects between oregano essential oil (EO) dietary supplementation and dynamic temperature change in sea bass. Under exposure to rising temperature (13-25 °C), fish were fed with a control diet (CD) and two experimental diets supplemented with 100 (D100) and 200 ppm (D200) of EO. Feed inclusion of EO promoted the activity of antioxidant enzymes in sea bass exposed to increasing temperature. Consistently with the temperature rise, TBARS concentrations increased in CD and D200 groups, whereas were almost stable in D100. Trend of blood glucose in fish fed on CD was likely affected by glycogenolysis and gluconeogenesis. Similarly, the depletion of triglycerides and cholesterol in fish fed on CD likely supported the energy cost of gluconeogenesis. On the other hand, the reduction of glucose, triglycerides, and cholesterol in D100 and D200 was mainly attributable to the hypoglycemic and hypolipidemic effects of EO. The higher levels of serum protein observed in D100 and D200 groups were also associated to a reduced thermal stress compared to CD. EO dietary supplementation may be a promising strategy to alleviate the negative effects of temperature shift on sea bass physiological and oxidative state.

Modulation of physiological oxidative stress and antioxidant status by abiotic factors especially salinity in aquatic organisms

Exposure to a variety of environmental factors such as temperature, pH, oxygen and salinity may influence the oxidative status in aquatic organisms. The present review article focuses on the modulation of oxidative stress with reference to the generation of reactive oxygen species (ROS) in aquatic animals from different phyla. The focus of the review article is to explore the plausible mechanisms of physiological changes occurring in aquatic animals due to altered salinity in terms of oxidative stress. Apart from the seasonal variations in salinity, global warming and anthropogenic activities have also been found to influence oxidative health status of aquatic organisms. These effects are discussed with an objective to develop precautionary measures to protect the diversity of aquatic species with sustainable conservation. Comparative analyses among different aquatic species suggest that salinity alone or in combination with other abiotic factors are intricately associated with modulation in oxidative stress in a species-specific manner in aquatic animals. Osmoregulation under salinity stress in relation to energy demand and supply are also discussed. The literature survey of >50 years (1960-2020) indicates that oxidative stress status and comparative analysis of redox modulation have evolved from the analysis of various biotic and/or abiotic factors to the study of cellular signalling pathways in these aquatic organisms.

Oxidative stress in benthic oligochaete worm, Tubifex tubifex induced by sublethal exposure to a cationic surfactant cetylpyridinium chloride and an anionic surfactant sodium dodecyl sulfate

The present study was assessed to determine the in vivo toxic effects of a cationic surfactant, cetylpyridinium chloride (CPC), and an anionic surfactant, sodium dodecyl sulfate (SDS) in terms of oxidative stress biomarkers in benthic oligochaete worm Tubifex tubifex for 14 days. The investigation demonstrated that sublethal concentrations of CPC (0.0213, and 0.0639 mg L^-1) and SDS (1.094 and 3.092 mg L^-1)induced paramount alterations in the oxidative stress enzymes in Tubifex tubifex. Superoxide dismutase (SOD), glutathione S-transferase (GST), reduced glutathione (GSH), and glutathione peroxidase (GPx) exhibited an initial notable increase in their activities in the surfactants exposed worms at 1d and 7d of exposure period followed by consequential reduction at 14d exposure period with respect to control, while catalase (CAT) and malondialdehyde (MDA) activities markedly incremented gradually throughout the exposure periods. Through the construction of the correlation matrix and integrated biomarker response (IBR), the effects of CPC and SDS on Tubifex tubifex were distinguished. These results indicate that exposure to these cationic and anionic surfactants modulates the levels of oxidative stress enzymes in Tubifex tubifex.

Effects on hematological parameters, antioxidant and immune responses, AChE, and stress indicators of olive flounders, Paralichthys olivaceus, raised in bio-floc and seawater challenged by Edwardsiella tarda

Studies on the resistance of fish raised in bio-floc systems against bacterial infection are limited. We aimed to evaluate the changes in hematological parameters, antioxidant and immune responses, stress indicators, and acetylcholinesterase (AChE) in olive flounder, Paralichthys olivaceus, raised in bio-floc and seawater for 10 months and, then, infected with Edwardsiella tarda at concentrations of 0 (control), 6.61 × 10⁴, 6.61 × 10⁵, 6.61 × 10⁶, and 6.61 × 10⁷ CFU/g fish for 7 days. The lethal concentration 50% was 4.32 × 10⁷ in bio-floc and 3.11 × 10⁶ in seawater. Hematological parameters were significantly decreased by E. tarda challenge, and plasma components were significantly changed. The superoxide dismutase, catalase, and glutathione-S-transferase activities, as antioxidant responses, were significantly increased after infection, whereas the reduced glutathione level was significantly decreased. The lysozyme activity was significantly increased and the AChE level was significantly decreased after infection. Cortisol and HSP 70, as stress indicators, were also significantly increased. The results indicate that E. tarda infection affected various physiological factors in P. olivaceus. Additionally, P. olivaceus raised in seawater were more susceptible to E. tarda infection than those raised in bio-floc.

Metabolites-Enabled Survival of Crucian Carps Infected by Edwardsiella tarda in High Water Temperature

Temperature is one of the major factors that affect the outbreak of infectious disease. Lines of evidences have shown that virulence factors can be controlled by thermo-sensors in bacterial pathogens. However, how temperature influences host's responses to the pathogen is still largely unexplored, and the study of this might pave the way to develop strategies to manage pathogenic bacterial infection. In the present study, we show that finfish Carassius carassius, the crucian carp that is tolerant to a wide range of temperatures, is less susceptible to bacterial infection when grown in 20°C than in 30°C. The different responses of C. carassius to bacterial infection could be partially explained by the distinct metabolisms under the specific temperatures: C. carassius shows elevated tricarboxylic acid cycle (TCA cycle) but decreased taurine and hypotaurine metabolism as well as lower biosynthesis of unsaturated fatty acids at 30°C. The decreased abundance of palmitate, threonine, and taurine represents the most characteristic metabolic feature. Consistently, exogenous palmitate, threonine, or taurine enhances the survival of C. carassius to bacterial infection at 30°C in a dose-dependent manner. This effect could be attributed to the inhibition on the TCA cycle by the three metabolites. This notion is further supported by the fact that low concentration of malonate, a succinate dehydrogenase inhibitor, increases the survival of C. carassius at 30°C as well. On the other hand, addition of the three metabolites rescued the decreased expression of pro-inflammatory cytokines including TNF-α1, TNF-α2, IL-1β1, IL-1β2, and lysozyme at 30°C. Taken together, our results revealed an unexpected relationship between temperature and metabolism that orchestrates the immune regulation against infection by bacterial pathogens. Thus, this study shed light on the modulation of finfish physiology to fight against bacterial infection through metabolism.

Changes in Hematological Parameters and Heat Shock Proteins in Juvenile Sablefish Depending on Water Temperature Stress

Juvenile Sablefish Anoplopoma fimbria were used to assess the effects of water temperature (8, 10, 12, 14, 16, 18, and 20°C) on hematological parameters and heat shock proteins 70 and 90 for 4 months. Hematological parameters, including red blood cell count, hematocrit, and hemoglobin, were significantly decreased at 18°C. The inorganic plasma components calcium and magnesium were not altered by water temperature. The organic plasma components glucose and cholesterol were notably elevated at 18°C, whereas total protein was reduced. The enzymatic components, including aspartate aminotransferase, alanine aminotransaminase, and alkaline phosphatase, were notably elevated at 16°C or 18°C. The results of this study indicate that a temperature higher than the proper temperature affects the hematological parameters and heat shock proteins of juvenile Sablefish.

Toxic effects of lead exposure on bioaccumulation, oxidative stress, neurotoxicity, and immune responses in fish: A review

Lead (Pb) is a highly toxic metal in aquatic environments. Fish are at the top of the food chain in most aquatic environments, and are the most susceptible to the toxic effects of Pb exposure. In addition, fish are one of the most abundant vertebrates, and they can directly affect humans through food intake; therefore, fish can be used to assess the extent of environmental pollution in an aquatic environment. Pb-induced toxicity in fish exposed to toxicants is primarily induced by bioaccumulation in specific tissues, and the accumulation mechanisms vary depending on water habitat (freshwater or seawater) and pathway (waterborne or dietary exposure). Pb accumulation in fish tissues causes oxidative stress due to excessive ROS production. Oxidative stress by Pb exposure induces synaptic damage and neurotransmitter malfunction in fish as neurotoxicity. Moreover, Pb exposure influences immune responses in fish as an immune-toxicant. Therefore, the purpose of this review was to examine the various toxic effects of Pb exposure, including bioaccumulation, oxidative stress, neurotoxicity, and immune responses, and to identify indicators to evaluate the extent of Pb toxicity by based on the level of Pb exposure.

Temperature affects the biology of Schmidtea mediterranea

Studies of tissue regeneration and host-pathogen interactions using the model planarian Schmidtea mediterranea have been performed at an experimental temperature of 19 °C. S. mediterranea planarians exposed to 19 °C–32 °C were observed for survival, mobility, feeding and regeneration for three months and elimination of the Staphylococcus aureus pathogen over six days. S. mediterranea planarians died at 30 °C–32 °C after 18 days of observation but tolerated temperatures of 19 °C up to 28 °C with non-significant differences in mobility and feeding behavior. Genetic malleability tested by RNAi feeding was still efficient at 26 °C and 28 °C. Concerning the immune capacity of planarians, we reported an exacerbation of the immune response in worms infected by S. aureus at 26 °C and 28 °C. These observations suggest a temperature modulation of planarian stem cells and illustrate the importance of modulating experimental temperature when using planarians as model organisms to study regeneration and immune response.

Experimental evidence of masculinization by continuous illumination in a temperature sex determination teleost (Atherinopsidae) model: is oxidative stress involved?

The present study evaluates the influence of continuous light on phenotypic sex ratios in Chirostoma estor, a temperature sex determination animal model. Relative gene expression levels of 5 day old larvae were performed on two early gonad differentiation genes (sox9 and foxl2), two stress axis activation genes (gcr1 and crf) and four reactive oxygen species (ROS) antagonist effector genes (sod2, ucp2, gsr and cat). Two light treatments were applied from fertilization; control (12L:12D) simulated natural photoperiod and a continuous illumination photoperiod. By the end of the trial (12 weeks after hatching), differentiated and normal gonads were clearly identifiable in both treatments by histological observations. Regarding sex ratio, 73% of phenotypic males were found in continuous illumination compared with 40% in controls. Consistently, the sox9 gene (involved in early testis differentiation) showed an over expression in 64% of the individual larvae analysed compared with foxl2 (ovarian differentiation) suggesting a masculinization tendency in continuous illumination. On the other hand, only 36% of individuals showed the same tendency in the control treatment consistent with phenotypic sex ratios found under normal culture conditions. Relative gene expression results did not show significant difference in sod2, ucp2 and gcr1 levels, but cat, gsr and crf showed significantly higher expression levels in the continuous illumination treatment suggesting that both, the stress axis and ROS response mechanisms were activated at this time. This study suggests, a link between continuous light, oxidative stress and environmental sex determination in vertebrates. However, further research is necessary to describe this possible upstream mechanism that may drive some aspects of sexual plasticity in vertebrates.

Antioxidant defense system, immune response and erythron profile modulation in gold fish, Carassius auratus, after acute manganese treatment

The manganese contamination has become a global problem, recently, because it is perceived as a real threat to the human health and the environment. It is well-known that overexposure to Mn²⁺ may have negative physiological effects on fish and other organisms inhabiting heavy metal polluted waters. To the best of our knowledge, studies relating with manganese effects on fish antioxidant enzyme response in the blood, immunocompetence and erythron profile alteration, are scarce. In this study, the acute sub-lethal effects of manganese on blood antioxidant response, immune status and erythron profile were determined by exposing the freshwater model organism, Carassius auratus, to two doses of this metal (3.88 ± 0.193 mg/L and 7.52 ± 0.234 mg/L Mn²⁺) for 96 h. Significant increases in blood antioxidant enzyme activity like superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST), were observed in fish exposed to manganese. Furthermore, plasmatic glucose and cortisol levels increased, while total protein decreased significantly. White blood cell differential count revealed a significant increase in monocyte and neutrophil number and a significant decrease of lymphocyte's number in fish exposed to manganese compared with those of control group. That can be considered as a clear evidence of altered immune system. Measured of erythron profile revealed a significant increasing of cellular and nuclear alteration of red blood cells, with karryorhectic, dividing and micronucleated erythrocytes in exposed fish, indicating the cytotoxic and genotoxic effects Mn²⁺ ions. Our data shown also that manganese could trigger antioxidant response, modulate immune response and induce erythron profile modification leading to eryptosis, compromising the blood oxygen carrying capacity, and overall health status in fish. This may suggest those parameters consider as useful biomarkers for monitoring effects of sub-lethal metal exposure on fish.