Abstract:The Amur ide (Leuciscus waleckii) in Lake Dali exhibits remarkable salt-alkali resistance, thriving in environments with an alkalinity of 53.57 mmol/L and pH of 9.6. It also demonstrates reproductive migration behavior, migrating annually to freshwater rivers to spawn. During this migration, the fish must face the transition of high-permeability to low-permeability water, which involves immense energy redistribution for basic metabolism and gonadal development. Steroid hormones, which are lipid hormones synthesized from cholesterol through a series of enzymatic reactions, play a crucial role in osmoregulation, gonadal development, and energy consumption during fish reproductive migration. To explore the role of steroid hormones in the osmoregulatory pressure mechanism of Leuciscus waleckii, we conducted a 10 d bidirectional cross-border stress experiment involving 50 mmol/L NaHCO₃ alkalinity stress followed by freshwater recovery. We analyzed serum steroid hormone levels, gene expression related to gill tissue in different treatment groups, and examined the methylation of key genes in promoter regions. Our results showed that differences in steroid hormones were primarily associated with three pathways. In the steroid biosynthesis pathway, the cholesterol and key genes involved (hsd17b7, ebp, dhcr24, and dhcr7) significantly increased in the alkalinity stress group (P＜0.05) and significantly decreased in the freshwater recovery group (P＜0.01). In the primary bile acid biosynthesis pathway, 25-hydroxycholesterol and 7α, 25-hydroxycholesterol, along with their target genes (ch25h and cyp7a1), significantly increased in the alkalinity stress group and significantly decreased in the freshwater recovery group (P＜0.01). In the steroid hormone biosynthesis pathway, Pregnenolone, 17α-hydroxyprogesterone, cortexolone, and cortisol significantly reduced in the alkalinity stress group (P＜0.001) and significantly increased in the freshwater recovery group (P＜0.05). Cholesterol, an intermediate product shared by these three pathways, also showed notable changes. Additionally, the promoter regions of the key genes involved in cholesterol synthesis and metabolism, ebp and sult2b1, exhibited low methylation levels in the alkalinity stress group and high methylation levels in the freshwater recovery group. These findings suggest that cholesterol is a crucial component of the steroid hormone-related pathways. It influences the methylation levels of key gene promoter regions involved in its synthesis and metabolism, thereby regulating the differential expression of other key genes in response to different environmental conditions. This regulation impacts the content of steroid hormones and plays a role in the osmoregulation of Leuciscus waleckii in varying environments. The results of this study provide a theoretical basis and scientific guidance for understanding the molecular mechanisms of fish alkali resistance, as well as for the transplantation and domestication of fish, and the cultivation of novel alkali-resistant varieties.

Abstract:High carbonate alkalinity in saline-alkaline water is considered a crucial factor that affects the survival of crustaceans. However, the information regarding the saline-alkaline adaptation mechanisms of Macrobrachium rosenbergii is currently limited. This study aimed to investigate the effects of saline-alkaline stress on the survival, enzyme activity, and transcriptomic profiling of M. rosenbergii by determining its semi-lethal concentration (LC₅₀) and lowest observed effect concentration (LOEC) of salinity and carbonate alkalinity for its larvae. Additionally, the study examined the effects of saline-alkaline stress on osmoregulation, antioxidant enzyme activities, and transcriptional expression in the gills and hepatopancreas of M. rosenbergii. Results showed that the 96 h-LC₅₀ of salinity for M. rosenbergii larvae was 27.1, with a 96 h-LOEC of 16.5, whereas the 96 h-LC₅₀ of carbonate alkalinity was 230.7 mg/L, with a 96 h-LOEC of 96.6 mg/L. Furthermore, salt-alkali interaction exhibited synergistic effects. Enzyme activity analysis revealed initial decreases followed by increases over time for alkaline phosphatase and Na⁺-K⁺-ATPase activities in the gills and hepatopancreas, whereas Ca²⁺-ATPase activity in the gills exhibited the opposite pattern. Superoxide dismutase activity in the hepatopancreas reached its lowest level during the mid-term stress period (72 h and 120 h), whereas catalase and glutathione S-transferase levels increased. Carbonic anhydrase activity showed an initial decrease followed by increase during the treatment process, with no significant differences observed among different saline-alkaline stress. Transcriptomic analysis revealed distinct responses of the gills and hepatopancreas to saline-alkaline stress. Up-regulated genes associated with extracellular space/region (e.g. tetraspanin), cellular response to xenobiotic stimulus (e.g. fatty aldehyde dehydrogenase), and secondary active transmembrane transporters were observed in the gills under saline-alkaline stress. Genes involved in the extracellular space/region were down-regulated in the hepatopancreas, whereas carbohydrate transmembrane transport related genes (e.g. lipocalin-like protein) were upregulated. These results suggest that M. rosenbergii adapts to saline-alkaline environments through coordinated osmotic regulation strategies, which include increased ion transport in the gills and enhanced carbohydrate transmembrane transport in the hepatopancreas. This study provides scientific evidence for understanding the adaptation mechanisms of M. rosenbergii in saline-alkaline environments.

Abstract: The diminishing availability of freshwater resources in recent years has led to a decrease in suitable areas for freshwater aquaculture, which in turn has prompted the use of saline-alkaline water to meet the growing demands. However, the limited application of saline-alkaline water, threatened by the presence of a single species in saline-alkaline aquaculture, notably impedes the development of saline-alkaline aquaculture. A comprehensive understanding of their physiological and molecular mechanisms of salt-alkaline tolerance is essential to cultivate species suitable for saline-alkaline aquaculture. Red tilapia (Oreochromis spp.) has good salinity tolerance; however, the metabolic response of red tilapia under an alkaline environment remains largely unclear. In this study, we compared serum physiological parameters, intestinal histology, and transcriptome in red tilapia between an alkalinity stress group [CA, (35.51±0.17) mmol/L] and a freshwater control group [Con, (1.75±0.08) mmol/L]. Exposure to the alkalinity condition for 40 d resulted in increased serum catalase (CAT) activity, total antioxidant capacity (TAOC), malondialdehyde (MDA), ammonia, and urea nitrogen (BUN) levels (P＜0.05), indicating an imbalance in ammonia excretion and antioxidant defense occurred in red tilapia under alkalinity stress; notable damage to intestinal fluff, thinning of the intestinal muscle layer, and damage to intestinal epithelial cells were also observed in the CA group, suggesting that alkalinity stress may disrupt normal gut physiological function. To investigate potential regulatory mechanisms associated with the observed biochemical and morphological alterations, we conducted a transcriptome analysis. Principal component analysis (PCA) revealed a clear separation of the samples from each group, suggesting high-quality data. Based on a log₂ (fold change)of ≥1 or≤ −1 and P ＜ 0.05, we identified a total of 2853 differentially expressed genes (CA vs. Con), including 1674 upregulated and 1179 downregulated genes. A total of 234 Gene Ontology (GO) items were found to be significantly enriched, such as signal transduction, transmembrane transport, and membrane. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed 112 key pathways in the intestine of red tilapia in response to alkaline stress, including endocytosis, biosynthesis of amino acids, intestinal immune network for IgA production, and NOD-like receptor signaling pathway. Gene Set Enrichment Analysis (GSEA) confirmed the activation of these four pathways under alkalinity stress. To verify the accuracy and reliability of the RNA-Seq data, a subset of 12 differentially expressed genes was chosen for qRT-PCR analysis. Correlation analysis revealed a strong linear relationship (R² = 0.880) between the gene transcript level data obtained using the two methodologies, thereby validating the reliability of the transcriptome sequencing data. Overall, our results suggest that alkalinity stress may damage the intestinal structure of red tilapia and induce oxidative stress. The changes in the expression of key genes involved in intestinal transport, metabolism, and immune response are crucial strategies for red tilapia to tolerate high alkaline conditions. Our study provides essential insights into the effects of alkaline water on the health and adaptive functions of red tilapia. Furthermore, it sets a crucial basis for future research on the molecular mechanisms that govern stress responses and tolerance to saline-alkaline exposure in fish.

Abstract:Saline-alkaline waters in China are widely distributed and are of various types, primarily carbonate and sulfate. Due to the high alkalinity of saline-alkaline waters, only a few low saline-alkaline waters can be used for freshwater fish farming. However, the area of saline-alkaline waters in China has been increasing annualy; therefore, an urgent need to take measures for the ecological treatment of soil salinization, exists. Litopenaeus vannamei has been widely chosen as a research object in recent years owing to its advantages, such as fast growth and strong environmental adaptability and research has been conducted on its tolerance to carbonate alkalinity. However, research lacks on the impact of sulfate-type water on Litopenaeus vannamei. Therefore, the present experiment was designed to investigate the effects of SO₄²⁻, a key saline ion in sulfate-type waters, on histological structure, immunity, antioxidant capacity, and ion transport capacity of Litopenaeus vannamei. First, the 96 h LC₅₀ of sulfate on Litopenaeus vannamei was determined to be 54.71 mmol/L by LC₅₀ experiment. Further, a control group (10 mmol/L SO₄²⁻) and an experimental group (60 mmol/L SO₄²⁻) were established and exposed for 96 h. At 0, 24, 48, 72, and 96 h of exposure, the shrimp hepatopancreas and gills were collected for pathological studies. At 0, 6, 12, 24, 48, 72, and 96 h of exposure, the hepatopancreas and gill tissues of Litopenaeus vannamei were collected for the determination of physiological indicators (ACP, AKP, SOD, GPX, CAT, MDA, NKA, and NHE). The results showed that: (1) The degree of damage to the hepatopancreas and gill of Litopenaeus vannamei increased gradually with the increase of stress time; (2) The activity of immunoenzymes (ACP and AKP) in hepatopancreas and AKP in gill showed an overall trend of “increase-decrease-increase-decrease-increase” with the increase of stress time; the activity of ACP in gill showed an overall trend of “increase-decrease-increase”; (3) With the increase of stress time, SOD, GPX and CAT in hepatopancreas showed an overall trend of “increase-decrease- increase-decrease” and the MDA content first increased and then decreased. In gill, SOD activity and MDA content showed the “increase-decrease-increase” trend, CAT activity showed the “decrease-incerase-decrease” trend, and GPX activity showed the “decrease-increase-decrease-increase” trend; (4) the activities of ion transporting enzymes (NKA and NHE) in gill showed the trends of “increase-decrease-increase” and “decrease-increase-decrease-increase” respectively, with the increase of stress time. These results indicate that Litopenaeus vannamei has a certain tolerance to sulfate and can adapt to the sulfate environment by regulating its own immune, antioxidant, and ion transport capacities. However, prolonged exposure would exceed the regulatory range of these physiological functions and cause severe damage to the hepatopancreas and gills of Litopenaeus vannamei, affecting its normal functions and eventually leading to mortality.

Abstract:A large area of China is covered by saline-alkali water with high salinity, high pH, and ion ratio imbalance. Macrobrachium rosenbergii is an economically important aquaculture species worldwide due to its rapid growth and low demand for animal feed. Considering the fact that the M. rosenbergii has wide adaptability to salinity and high resistance to alkalinity stresses, an experiment was conducted to investigate the effects of carbonate alkalinity stress on the growth, reproduction, and intestinal health of M. rosenbergii to effectively utilize the abandoned saline-alkali water in China and establish a model of inland saline-alkali water cultured M. rosen­bergii. Juvenile M. rosenbergii [(2.85±0.12) g] were subjected to an acute carbonate alkalinity stress experiment to determine the 96-hour lethal concentration (LC₅₀). Based on this, four carbonate alkalinity concentrations, i.e., 1.5 (control group), 3, 6, and 9 mmol/L, designated as control C1, C3, C6, and C9, respectively, were used to culture triplicate groups for 56 d. The results showed that the 96-hour LC₅₀ value for juvenile M. rosenbergii under carbonate alkalinity stress was 17.955 mmol/L, with a safe concentration of 5.118 mmol/L. The survival, weight gain, and specific growth rates of juveniles decreased with increasing alkalinity concentrations, with significant reductions observed in the C9 group compared with the other experimental groups (P＜0.05). The feed conversion ratio in the C9 group was significantly higher than that in the other experimental groups (P＜0.05). Compared with the control group, carbonate alkalinity in the C6 and C9 groups significantly inhibited the spawning and egg incubation rates of adult prawns (P＜0.05). Transmission electron microscopy revealed that the structural integrity of the intestinal microvilli in juvenile prawns deteriorated with increasing carbonate alkalinity stress, with the most severe damage observed in the C9 group. Furthermore, the present study found that the intestinal peritrophic membrane structure of juvenile prawns was damaged by a higher concentration of carbonate alkalinity; and the peritrophic matrix structure of prawns in the C9 group using scanning electron microscopy technology showed increased damage and enlarged pore sizes under carbonate alkalinity stress. Alpha diversity analysis of the intestinal microbiota of juvenile prawns using Illumina MiSeq high-throughput sequencing showed that the flora richness index Chao1 in the C9 group had no significant diffrence from that of the control group (P＞0.05), but was significantly higher than that of C3 and C6 groups (P＜0.05). There was no significant difference in Shannon and Simpson intestinal flora diversity index among all experimental groups (P＞0.05). Proteobacteria, Bacteroidetes, Planctomycetes, Cyanobacteria, Actinobacteria, and Firmicutes dominated the bacterial communities of juvenile M. rosenbergii at the phylum level. At the genus level, the abundances of the pathogenic bacteria Flavobacterium and Pseudomonas in the C9 group were significantly higher than those in the control group (P＜0.05), suggesting that changes in the gut microbiota structure of juvenile M. rosenbergii exhibit an increased risk of disease outbreaks. These results suggested that chronic higher concentrations of carbonate alkalinity stress significantly affect the growth performance and reproductive and intestinal histology of juvenile prawns and disrupt the intestinal microbial community structure. Our study highlights that M. rosenbergii juveniles are suitable for large-scale saline-alkaline aquaculture in China.

Abstract:The use of saline-alkaline water for aquaculture has become a notable method for the comprehensive utilization of water and land resources in saline-alkaline soil. Litopenaeus vannamei is an important species in saline-alkaline aquaculture. The microbial community in water plays an important role in aquaculture processes. However, the dynamic changes of bacterioplankton throughout the entire process in shrimp farming ponds in saline-alkaline soil should be investigated to reveal the microbiota characteristics. In the present study, 16S rRNA high-throughput sequencing technology and Illumina MiSeq sequencing platforms were used to analyze the bacterioplankton in the water samples from saline-alkaline L. vannamei aquaculture ponds in the Hetao Plain of Inner Mongolia. Forty-three phyla and 1004 bacterial genera were detected in samples collected at seven time points. Firmicutes (33.82%), Proteobacteria (25.82%), Cyanobacteria (17.36%), and Actinobacteria (17.36%) were the phyla with more than 10% abundance and they showed significant differences between different samples. At the genus level, the dominant genera were Exiguobacterium, Psychrobacter, and Cyanobium_PCC-6307 and their abundance were significantly different among all groups. Exiguobacterium were enriched during the early and middle stage (0–30 d, 19.57%–55.17%), with less relative abundance during the later stage (40–60 d, 13.32%–24.84%). Psychrobacter was less abundant on Day 0, Day 10, and Day 40 (0.07%–0.53%); however, its relative abundance increased notably on Day 50 (49.21%). Cyanobium_PCC-6307 showed an increase in abundance on Day 40, with small fluctuations in the remaining samples (3.87%–13.12%). Planococcus had the highest relative abundance in the water before the release of shrimp (9.68%) and decreased during the later culture stage. Massilia and Chryseobacterium were specifically enriched only on Day 30. Cyanobacteria could be considered as the major threat in inland saline-alkaline water aquaculture, with a low abundance of Vibrio. Exiguobacterium and Psychrobacter can be considered as the chief probiotics in the water source and saline-alkaline pond because of their ability to inhibit the bloom of Cyanobacteria. Unique bacterioplankton communities were formed in different aquaculture stages, with water temperature and nitrogen and phosphorus nutrients driving the succession of bacterioplankton communities.

Abstract:Saline-alkaline water resources in China are widely distributed. Saline-alkaline water is characterized by a high pH value, carbonate alkalinity, and ion coefficient. Therefore, regulating water quality has become a key challenge and focus of saline-alkaline aquaculture. Frequent outbreaks of harmful Cyanobacteria in saline-alkaline ponds severely affect the healthy growth of aquaculture organisms. Microcystis spp. is one among the major harmful Cyanobacteria. Currently, the primary methods for controlling harmful Cyanobacteria include physical, chemical, and biological methods. However, physical or chemical methods for preventing and controlling algal blooms have certain limitations, such as being time-consuming, labor-intensive, heavy pollutants, and prone to recurrence. Biological methods, such as the use of algicidal bacteria, are highly efficient and safe, making them a hot research topic. In the aquaculture industry, Bacillus species with algicidal properties, such as Bacillus subtilis, Bacillus cereus, Lysinibacillus fusiformis, and Brevibacillus laterosporus are receiving increasing attention from researchers. However, a few reports are available on algicidal bacteria against harmful Cyanobacteria in saline-alkaline ponds. The Ningxia Hui Autonomous Region, located in the northwest of China, has several northwest sulfate-type saline-alkaline ponds. In this study, we selected a strain of B. cereus TC-1, which was isolated and screened from the microalgae environment in saline-alkaline ponds of Ningxia Hui Autonomous Region. The growth adaptability of this strain was studied under different conditions of salinity (5, 15, 25, and 35), pH (4.0, 6.0, 8.0, and 10.0), temperature (10 ℃, 20 ℃, 30 ℃, and 40 ℃), and alkalinity (4.0 mmol/L, 8.0 mmol/L, 12.0 mmol/L, and 16.0 mmol/L). Additionally, its algal solubilization effects on two kinds of Microcystis were explored. Using nutrient agar culture medium, the bacterial density of each experimental group was determined on days 0, 2, 4, 6, and 8. The results showed that strain TC-1 grew well under conditions of salinity of 5–35, pH 6.0–10.0, temperature of 20 ℃–40 ℃, and alkalinity of 4.0–16.0 mmol/L. The best growth was observed under conditions of salinity of 15, pH 8.0, temperature of 30 ℃, and alkalinity of 12.0 mmol/L, with a bacterial density of (1.14±0.16)×10⁸ CFU/mL. In the co-cultivation system of saline-alkaline water with alkalinity of 4.0 mmol/L and 12.0 mmol/L, the algicidal effects of strain TC-1 on Microcystis aeruginosa and Microcystis sp. were significant. After the action of B. cereus strain TC-1, phenomena, such as fading, cell wall rupture, blurred and deformed edges, and protoplast efflux were observed, resulting in a significant decrease in the algal density. On the 6th day, the algicidal rate of strain TC-1 reached (82.83±0.03)% to (91.67±0.10)%. The results indicate that strain TC-1 has good adaptability to environmental factors, such as salinity, pH, temperature, and alkalinity which is generally consistent with the variation range of salinity, temperature, and pH in most saline-alkaline pond water. It has a good algicidal effect on Microcystis spp. and can be used as a candidate strain for the prevention and control of Microcystis blooms in saline-alkaline ponds.

Abstract:Several studies have shown that the use of saline-alkaline water can impact the muscle quality of farmed animals. However, it was unclear whether the meat quality of Exopalaemon carinicauda, which had been successfully cultured in saline-alkaline waters, had also been affected. To investigate the effect of saline-alkaline water on the meat quality of E. carinicauda, data references for production and selective breeding were provided. Three groups of E. carinicauda were selected, including “Huangyu No.1” cultured in saline-alkaline water (salinity 15, carbonate alkalinity 7.25 mmol/L, CHY), “Huangyu No.1” cultured in marine water (salinity 30, carbonate alkalinity 2 mmol/L, HY), and wild populations (salinity 30, carbonate alkalinity 2 mmol/L, WP); each consisting of 30 shrimps. The basic nutrient content, total sugar content, amino acid, and fatty acid content in the muscle of the three groups were measured. Amino acid score (AAS), chemistry score (CS), and essential amino acid index (EAAI) were used to evaluate the amino acid content. The composition and quality of the meat were systematically analyzed and evaluated. Finally, catalase (CAT) activity, superoxide dismutase (SOD) activity, and total antioxidant capacity (T-AOC) in shrimp meat of the three groups were detected. The results indicated that the total sugar content of the HY group was significantly lower than that of the WP group (P＜0.05), and the content of lysine (Lys), leucine (Leu), and isoleucine (Ile) was significantly higher than that of the WP group (P＜0.05). The moisture content of the CHY group was significantly higher than that of the HY group (P＜0.05), while the crude protein and crude ash contents were significantly lower than those of the HY group (P＜0.05). The total amount of amino acids (TAA), essential amino acids (EAA), and delicious amino acids (DAA) in the muscle of the CHY group were significantly lower than those of the HY group (P＜0.05). The EAA/TAA ratio of the three groups ranged from 34.45% to 37.54%, whereas the EAA/non-essential amino acids (NEAA) ratio ranged from 63.82% to 71.38%. Among the amino acids present in shrimp meat, glutamic acid (Glu), aspartic acid (Asp), and Lys were the most abundant. In the CHY group, 15 fatty acids were identified, while 12 fatty acids were identified in the HY and WP groups. The content of polyunsaturated fatty acids (PUFA) in the CHY group was significantly higher than that in the HY and WP groups (P＜0.05). The enzyme activity results revealed that the antioxidant capacity of shrimp in the CHY group was lower than that in the HY group. In conclusion, the nutritional value of the CHY and HY groups was comparable to that of the WP group, all of which were considered high-quality foods. The meat of the CHY group was high in moisture and unsaturated fatty acids and low in crude protein. In terms of lipid nutrition, it surpassed the HY group. The saline-alkaline water used in the study reduced the flavor of the muscles of E. carinicauda and altered their nutritional quality. The findings of this study demonstrate that E. carinicauda can maintain excellent nutritional quality after long-term survival in saline-alkaline water, providing a basis for the sustainable development of saline-alkaline water fisheries.

Abstract:Artemia is a tiny crustacean that lives in high-salinity waters and is widely distributed in inland salt lakes and coastal salt pans. Artemia is not only an important participant in the food chain of hypersaline water ecosystems, but also a crucial live food for aquatic animals. The Qinghai-Tibet Plateau is one of the regions with the most abundant salt lakes and Artemia resources in China. In recent years, the Qinghai-Tibet Plateau has experienced warming and changing precipitation patterns. Fresh water from melting glaciers and snow on the Qinghai-Tibet Plateau continuously flows into plateau lakes, leading to lake expansion and salinity reduction, which may further cause the survival crisis of Artemia in these lakes. To explore the effects of climate warming and salt lake salinity decline on the morphology and genetic characteristics of plateau salt lake organisms over the past 20 years, we selected the 1996 and 2021 Artemia populations from Lagkor Co (LGC) for culture and morphological measurement. In addition, the genetic diversity and structure of Artemia were analyzed using specific-locus amplified fragment sequencing (SLAF-seq). This study observed that although the decrease in LGC salinity in the last 25 years had negligible effect on the overall morphological changes in Artemia, the compound eye distance, second antennal length and periplieral grasping apparatus length were significantly higher in 1996 than that in 2021 (P＜0.01). A total of 229.12 Mb of read data were obtained by SLAF-seq, with an average sequencing Q30 of 92.40% and an average GC content of 36.96%. Furthermore, 263069 polymorphic SLAF tags were developed, and 680955 SNP markers were selected for population genetic analysis. Genetic diversity analysis showed that the LGC-1996 population was larger than the LGC-2021 population in E_a, O_a, and H_o indices and smaller than the LGC-2021 population in other indices; however, the overall genetic diversity difference between the two Artemia populations was small. The polymorphism information content (PIC) values for LGC-1996 and LGC-2021 were 0.268 and 0.269, respectively, indicating moderate polymorphism (0.25＜PIC＜0.5). The genetic differentiation coefficient (F_st) value between the two populations was 0.106, indicating a moderate degree of genetic differentiation (0.05＜F_st＜0.15). Phylogenetic tree analysis, principal component analysis, and kinship heat map analysis further showed obvious clustering differences between these two populations. The Admixture analysis showed that K=1 is the optimal number of subpopulations, which indicated that these two Artemia populations have differentiated to a certain extent over time, however, have not differentiated into two completely independent populations and their genetic information comes from the same original ancestor. These changes in morphological characteristics and genetic differences may be due to the decrease in salinity caused by climate warming and the genetic drift that LGC has experienced in recent years. In addition, considering the overall low level of genetic diversity and the potential threat of environmental change, developing and improving the monitoring, assessment, and protection system of Artemia resources in salt lakes of Tibet is necessary. This study not only contributes to a comprehensive understanding of the impact of climate warming on Artemia populations, but also provides theoretical support for the conservation and utilization of Artemia germplasm resources in Tibet. Key words: Qinghai-Tibet Plateau; Artemia; genetic diversity; genetic structure; germplasm resources; climate warming; saline-akali water

Abstract:To investigate the physiological adaptability of the Chinese mitten crab (Eriocheir sinensis) to saline-alkali water environments from the Yellow River estuary, we constructed various gradients of salinity and alkalinity, as well as single-factor stress of salinity (14 and 35 mmol/L) and alkalinity (26 and 55 mmol/L) and combined saline-alkali stress (salinity, 6 and 14 mmol/L; alkalinity, 10 and 26 mmol/L). The crabs were subjected to a continuous saline-alkali stress treatment for 96 h. We examined the survival rate of E. sinensis under saline-alkali stress and the structural changes in the gill tissues (anterior and posterior) and hepatopancreas. Additionally, the activity of the antioxidant enzyme superoxide dismutase (SOD) and concentration of glutathione (GSH) in these tissues were measured. The results showed that E. sinensis from the Yellow River estuary had notable tolerance to sodium chloride salinity and sodium bicarbonate alkalinity. The lethal concentration 50 (LC₅₀) values at 24, 48, 72, and 96 h were 65.90, 55.39, 53.29, and 50.14 mmol/L, respectively, with a safe concentration of 13.97 mmol/L. For alkalinity stress, the LC₅₀ values at 24, 48, 72, and 96 h were 119.4, 86.48, 64.49, and 58.98 mmol/L, respectively, with a safe concentration of 25.96 mmol/L. Histological assessments showed that under saline-alkali stress, the anterior gills suffered more damage than the posterior gills possibly because of their roles in maintaining osmotic balance and ion exchange; thus, the posterior gills showed stronger tolerance to saline-alkaline stress than the anterior gills. Moreover, alkalinity stress caused more severe damage at the tissue level than salinity stress; furthermore, the degree of damage caused by the saline-alkaline interactive stress further exceeded that of the damage caused by the individual stress factors. Under the continuous 96 h-saline-alkali stress, the SOD activity and GSH concentration in the anterior and posterior gills of E. sinensis first increased and then decreased. After 72 h, the SOD activity and GSH concentration significantly decreased to below the initial levels; the SOD activity in the hepatopancreas significantly decreased after 24 h. These results indicate that E. sinensis can activate its antioxidant system to adapt to saline-alkali stress; however, when the intensity of environmental stress exceeds the coping capacity of its antioxidant system, the activity of antioxidant enzymes is suppressed.