Gut microbiota dysbiosis triggered by salinity stress enhances systemic inflammation in spotted scat (Scatophagus argus)

As an ecological disturbance, salinity changes substantially impact aquatic organism health. Gut microbiota plays a pivotal role in host health and exhibits heightened sensitivity to environmental salinity stress; however, the potential correlative mechanisms between gut microbiota dysbiosis triggered by salinity changes and host health remain unclear. The present study conducted a 4-week stress experiment to investigate the precise impact of gut microbiota on the inflammatory response in Scatophagus argus under different salinities (0 ‰ [hyposaline group, HO], 25 ‰ [control group, CT], and 40 ‰ [hypersaline group, HE]). Our results revealed that both HO and HE stress significantly changed the relative abundances of Gram-negative bacteria and the impairment of intestinal barrier function. Subsequently, the levels of lipopolysaccharide (LPS) in the serum exhibited a significant increase, and the expression levels of genes (tlrs, myd88, irak1, irak4, and traf6) involving TLRs/MyD88/NF-κB signaling pathway and pro-inflammatory cytokines (il-6, il-8, il-1β, and tnf-α) in the representative immune organs were significantly upregulated. Conversely, the abundance of the anti-inflammatory gene (tgf-β1) and its protein contents in serum were decreased. Transplantation of the gut microbiota from S. argus exposed to varying salinities into germ-free Oryzias latipes resulted in an enhanced inflammatory response. Our results suggested that both HO and HE stress increased the presence of Gram-negative bacteria and disrupted the intestinal barrier, leading to elevated serum LPS and subsequent systemic inflammation in fish. These findings provide innovative insights into the influence of salinity manipulation strategies on the health of aquatic organisms, contributing to the mariculture management in coastal areas.

Aquatic Organisms in Response to Salinity Stress: Ecological Impacts, Adaptive Mechanisms, and Resilience Strategies

Salinity stress presents a major ecological challenge for aquatic organisms, particularly in environments where salinity levels fluctuate. These fluctuations are becoming more pronounced due to climate change, further destabilizing aquatic ecosystems. Understanding how organisms adapt to such variability is essential for biodiversity conservation and the sustainable management of aquatic resources. This review examines the physiological, molecular, and behavioral adaptations that enable aquatic organisms to survive and thrive under salinity stress. Specifically, it explores mechanisms of osmotic regulation, ion transport, and oxidative stress responses, highlighting key signaling pathways-such as AMP-activated protein kinase (AMPK), Phosphatidylinositol 3-kinase-protein kinase (PI3K-AKT), Mitogen-activated protein kinase (MAPK), and the Hippo pathway-that facilitate these adaptive processes. The review also emphasizes the genetic and epigenetic modifications that contribute to resilience, underscoring the importance of genetic diversity for species survival in fluctuating salinity conditions. Furthermore, the interactions between host organisms and their microbiomes are discussed as critical factors influencing resilience. The review addresses the impact of salinity fluctuations on species distribution and biodiversity, with a focus on the implications of climate change for aquatic ecosystems. Finally, strategies for mitigating salinity stress, such as nutritional interventions and the development of salinity-resistant varieties, are explored, particularly in aquaculture. Overall, this review consolidates current knowledge on organismal adaptations, molecular mechanisms, and environmental challenges, offering valuable insights for ecological research and aquaculture practices in the face of climate change.

Rainbow Trout (Oncorhynchus mykiss) Pre-Smolts Treated with 11-Deoxycorticosterone Regulate Liver Carbohydrate Metabolism and Gill Osmoregulation

Smoltification is stressful for salmonids, and cortisol is one of the central endocrine regulators for seawater adaptation. It has been established that cortisol plays both mineralocorticoid and glucocorticoid functions by MR and GR, respectively, since the aldosterone hormone is absent. Recently, investigations have proposed that the 11-deoxycorticosterone (DOC) mineralocorticoid precursor might support cortisol effects, but this mechanism remains unclear. Hence, we assessed the early effects of DOC on rainbow trout pre-smolts, the key smoltification stage, via metabolic and transcriptomic approaches. Thirty-six juveniles (~120 g) were treated for 3 h with DOC (1 mg/kg) and/or mineralocorticoid (eplerenone) or glucocorticoid (mifepristone) receptor antagonists (n = 6 for each group). DOC decreased plasma glucose and pyruvate and increased phosphate and liver glycogen. DOC also downregulated carbohydrate metabolism-related genes in the liver. Finally, gill RNA-seq analysis presented 1660 differentially expressed transcripts in DOC versus vehicle, 1022 for eplerenone + DOC versus DOC and 3324 for mifepristone + DOC versus DOC. The enrichment analysis mainly revealed the upregulation of ion transmembrane transport and carbohydrate metabolism and the downregulation of stress and innate immune responses. This suggests a significant role of DOC in liver carbohydrate metabolism and gill osmoregulation of pre-smolts through both receptors. Hence, this could contribute to improving animal welfare monitoring during smoltification by featuring novel and potential biomarkers.

Salinity Tolerance in Freshwater Drum (Aplodinotus grunniens): Investigating Biochemical, Antioxidant, Digestive Enzyme, and Gene Expression Responses to Acute Salinity Stress

Variations in salinity levels in aquaculture significantly influence fish physiology, impacting population dynamics and industry viability. This study aimed to examine the physiological response of the freshwater drum (Aplodinotus grunniens) to differing salinity conditions, assessing its potential for cultivation in brackish water environments. Fish averaging 45 ± 0.1 g were subjected to acute salinity tests across three groups: a control group at 0‱ and experimental groups at 7.5‱ and 15‱ over four days. The initial findings indicated that A. grunniens could tolerate salinity levels up to 15‱ without adverse effects. Key biochemical markers, such as aspartate aminotransferase and alanine aminotransferase, exhibited significant fluctuations but decreased over time. Antioxidant enzyme activity increased relative to the control, while malondialdehyde levels declined, indicating effective oxidative stress management. Additionally, digestive enzymes like amylase and lipase demonstrated adaptability to changing salinity. The expression of heat shock proteins 70 and 90 in the gills and livers varied initially but showed no sustained changes. Overall, the results suggest that A. grunniens possesses notable resilience to salinity variations, indicating its suitability for brackish water aquaculture and highlighting the optimal salinity ranges for promoting growth.

Effects of salinity stress on the growth performance, histological characteristics, and expression of genes related to apoptosis and immunity in channel catfish (Ictalurus punctatus)

Salinity is an important environmental factor affecting fish growth and development. To investigate the effects of salinity stress on the growth performance, tissue structures, and expression of genes related to apoptosis and immune response in large-sized channel catfish (Ictalurus punctatus) juveniles, an 8-week salinity stress experiment was conducted. Six salinity levels (3, 3.8, 4.7, 5.9, 7.3, and 9 psu) were set according to an equal logarithmic concentration gradient method, along with a control group (0), and growth performance and physicochemical indices were measured. The survival rate of channel catfish in all salinity groups was 100%. Body length, body weight, weight gain rate, and specific growth rate decreased with increasing salinity, with higher salinity levels resulting in more significant reductions in growth performance. At 9 psu, both the specific growth rate (SGR) and weight gain rate (WGR) decreased significantly to 0.61%/day and 40.86%, respectively (p < 0.05). Histological analysis results indicated that with the increase in salinity, the number of intestinal mucosal folds relatively increased, while the number of goblet cells gradually decreased. Hepatocytes became more densely packed, and the hepatic lobule gaps widened. Apoptosis detection results revealed that in the liver, the number of apoptotic cells at 4.7 psu salinity was more than that in the control group and at 9 psu salinity. In the intestine, the number of apoptotic cells at 9 psu salinity was significantly higher than in the other two groups (p < 0.05). Quantitative polymerase chain reaction (qPCR) analysis of the expression patterns of genes related to apoptosis and immunity showed that the expression levels of caspase 3, caspase 8, INF-I, IL-1β, and bax genes in the liver and intestinal tissues were higher in the experimental groups than in the control group, while the expression of bcl-2 decreased with increasing salinity in liver tissue but increased in intestinal tissue. These findings can provide theoretical guidance for the aquaculture of channel catfish in saline-alkali land.

A TMT-Based Proteomic Analysis of Osmoregulation in the Gills of Oreochromis mossambicus Exposed to Three Osmotic Stresses

Salinity and alkalinity are critical environmental factors that affect fish physiology and ability to survive. Oreochromis mossambicus is a euryhaline species that can endure a wide range of salinities and has the potential to serve as a valuable model animal for environmental science. In order to detect the histomorphological changes, antioxidant enzymes, and proteomic responses of O. mossambicus to different osmotic stresses, O. mossambicus was subjected to salinity stress (25 g/L, S_S), alkalinity stress (4 g/L, A_S), saline-alkalinity stress (salinity: 25 g/L, alkalinity: 4 g/L, SA_S), and freshwater (the control group; C_S). The histomorphological and antioxidant enzyme results indicated that salinity, alkalinity, and saline-alkalinity stresses have different degrees of damage and effects on the gills and liver of O. mossambicus. Compared with the control, 83, 187, and 177 differentially expressed proteins (DEPs) were identified in the salinity, alkalinity, and saline-alkalinity stresses, respectively. The obtained DEPs can be summarized into four categories: ion transport channels or proteins, energy synthesis and metabolism, immunity, and apoptosis. The KEGG enrichment results indicated that DNA replication and repair were significantly enriched in the salinity stress group. Lysosomes and oxidative phosphorylation were considerably enriched in the alkalinity stress group. Comparatively, the three most important enriched pathways in the saline-alkalinity stress group were Parkinson's disease, Alzheimer's disease, and Huntington's disease. The findings of this investigation yield robust empirical evidence elucidating osmoregulatory mechanisms and adaptive biological responses in euryhaline teleost, thereby establishing a scientific foundation for the cultivation and genomic exploration of high-salinity-tolerant teleost species. This advancement facilitates the sustainable exploitation of saline-alkaline aquatic ecosystems while contributing to the optimization of piscicultural practices in hypersaline environments.

Transcriptomics and proteomics provide insights into the adaptative strategies of Tibetan naked carps (Gymnocypris przewalskii) to saline-alkaline variations

Gymnocypris przewalskii is an exclusively cyprinid fish that inhabits Lake Qinghai, which is characterized by high salinity and alkalinity. To elucidate the molecular basis of the adaptation of G. przewalskii to a wide range of salinity‒alkalinity conditions, we performed morphological, biochemical, transcriptomic and proteomic analyses of the major osmoregulatory organs of the gills and kidney. Morphological examination revealed that mitochondria-rich cells were replaced by mucus cells in the gills during the transition of G. przewalskii from freshwater to lake water. In the kidney, the tight junction formed dense structure in the renal tubules under lake water condition compared with the loose structure in freshwater. The results of the biochemical assays revealed an increased content of total amino acids, indicating their potential roles as osmolytes and energy supplies in freshwater. The decreased urea concentration suggested that urea synthesis might not be involved in the detoxicity of ammonia. The transcriptomic and proteomic data revealed that genes involved in ion absorption and ammonia excretion were activated in freshwater and that genes involved in cell junction and glutamine synthesis were induced in lake water, which was consistent with the morphological and biochemical observations. Together with the higher levels of glutamine and glutamate, we proposed that G. przewalskii alleviated the toxic effect of ammonia direct excretion through gills under freshwater and the activation of the conversion of glutamate to glutamine under high saline-alkaline condition. Our results revealed different expression profiles of genes involved in metabolic pathways, including the upregulation of genes involved in energy production in freshwater and the induction of genes involved in the synthesis of acetylneuramic acid and sphingolipid in soda lake water. In conclusion, the appearance of mitochondria-rich cells and increased energy production might contribute to ion absorption in G. przewalskii to maintain ion and solute homeostasis in freshwater. The existence of mucus cells and dense junctions, which are associated with increased gene expression, might be related to the adaptation of G. przewalskii to high salinity-alkalinity.

The impact of bisphenol A on gill health: A focus on mitochondrial dysfunction induced disorders of energy metabolism and apoptosis in Meretrix petechialis

Bisphenol A (BPA), a well-known chemical compound used in various daily goods, has been associated with adverse effects on animal metabolic processes. However, the specific impacts of BPA exposure on clam gills remain largely unexplored. To investigate the effects of BPA on energy metabolism and apoptosis in Meretrix petechialis gills, clams were exposed to varying concentrations of BPA (1, 10, and 100 μg/L) for 21 days. Results showed that BPA exposure induced gill histopathological injuries and inhibited filtration rates. Transmission electron microscopy (TEM) analysis revealed mitochondrial injury and dysfunction as potential mechanisms of gill damage. Transcriptome analysis identified differentially expressed genes (DEGs) primarily enriched in energy metabolism and apoptosis pathways. BPA-induced changes in ATP content, ATPase, and lactate dehydrogenase (LDH) activities suggested dysregulation of energy metabolism. TUNEL staining demonstrated enhanced apoptotic signals with increasing BPA concentrations. Activation of the caspase-3/9 pathway indicated a concentration-dependent, mitochondria-dependent apoptotic process. Additionally, the expression of genes associated with mitochondria (NNT, TOMM40, and SLC25A11), energy metabolism (PCK1 and pdhC), inducing mitochondria-dependent apoptosis (NFKB1, RAC1, and TRAF2), and oxidative stress (GSTT1) was affected by BPA exposure. Integrated biomarker response version 2 (IBRv2) values further confirmed a concentration-dependent gill toxicity of BPA via the mitochondrial pathway. These findings provide a deeper understanding of the toxicological mechanisms underlying BPA-induced toxicity in bivalves and contribute to assessing the risks posed by BPA in benthic ecosystems.

N6-methyladenosine RNA methylation regulates microplastics-induced cell senescence in the rainbow trout liver

Microplastics are prevalent in aquatic ecosystems, impacting various forms of aquatic life, including fish. In this study, Rainbow trout (Oncorhynchus mykiss) were exposed to two concentrations of microplastics (0 and 500 μg/L) over a 14-day period, during which a comprehensive analysis was conducted to assess the liver accumulation of microplastics and their effects on oxidative stress, the liver response, and transcriptomics. Our findings indicated that microplastics significantly accumulated in the liver and activated the antioxidant system in fish by enhancing the activity of antioxidant enzymes. Histological lesions were also observed in the liver of the fish. Furthermore, microplastics induced alterations in the expression of hepatic N6-methyladenosine readers, specifically downregulating IGF2BP1 (encoding insulin like growth factor 2 mRNA binding protein 1) and upregulating YTHDF2 (encoding YTH N6-methyladenosine RNA binding protein F2), which in turn decreased mRNA stability and reduced the expression of C-myc and other regulatory factors involved in the cell cycle and proliferation. This sequence of events resulted in slowed cell proliferation, the induction of cell cycle arrest, and the promotion of cellular senescence. This study offers valuable insights into the toxicological mechanisms of microplastics and enhances our understanding of the threats that plastic pollution poses to freshwater organisms.

Salty surprises: Developmental and behavioral responses to environmental salinity reveal higher tolerance of inland rather than coastal Bufo spinosus tadpoles

Salinization is predicted to intensify due to climate change, impacting biodiversity and ecosystem functioning. Amphibians, particularly embryos and larvae, are highly susceptible to environmental salinity. Yet, local adaptation may cause differing vulnerabilities between coastal and inland populations. In this study, we investigated the physiological, behavioural, and life-history responses to environmental salinity (0, 2 and 4 g l-1) of embryos and larvae of a widespread amphibian species (spined toad, Bufo spinosus) from salt-exposed (coastal) and salt-free (inland) populations. Moderate salinity (4 g l-1) altered embryonic and larval development in both populations, causing increased malformations, decreased body size and survival, and altered behavior, but did not affect telomere length or oxidative status. Individuals exposed to low salinity (2 g l-1) performed better across most traits. However, moderate salinity had stronger negative effects on coastal individuals, indicating a lack of local adaptation and overall lower performance compared to their inland counterparts. These findings suggest that increasing salinity will have varied impacts on organisms depending on their population origins and developmental stages.

Gene expression signatures between Limia perugiae (Poeciliidae) populations from freshwater and hypersaline habitats, with comparisons to other teleosts

Salinity gradients act as strong environmental barriers that limit the distribution of aquatic organisms. Changes in gene expression associated with transitions between freshwater and saltwater environments can provide insights into organismal responses to variation in salinity. We used RNA-sequencing (RNA-seq) to investigate genome-wide variation in gene expression between a hypersaline population and a freshwater population of the livebearing fish species Limia perugiae (Poeciliidae). Our analyses of gill gene expression revealed potential molecular mechanisms underlying salinity tolerance in this species, including the enrichment of genes involved in ion transport, maintenance of chemical homeostasis, and cell signaling in the hypersaline population. We also found differences in gene expression patterns associated with cell-cycle and protein-folding processes between the hypersaline and freshwater L. perugiae. Bidirectional freshwater-saltwater transitions have occurred repeatedly during the diversification of fishes, allowing for broad-scale examination of repeatable patterns in evolution. Therefore, we compared transcriptomic variation in L. perugiae with other teleosts that have made freshwater-saltwater transitions to test for convergence in gene expression. Among the four distantly related population pairs from high- and low-salinity environments that we included in our analysis, we found only ten shared differentially expressed genes, indicating little evidence for convergence. However, we found that differentially expressed genes shared among three or more lineages were functionally enriched for ion transport and immune functioning. Overall, our results-in conjunction with other recent studies-suggest that different genes are involved in salinity transitions across disparate lineages of teleost fishes.

Dietary salt concentrations influence growth, nutrient utilization, and fatty acid profiles of turbot (Scophthalmus maximus) reared in brackish water

Expansion of economically viable turbot (Scophthalmus maximus) aquaculture depends on access to brackish-cold ground water sources in various parts of the world. Since brackish water sources can adversely affect the physiology and zoo technical performance of fish due to the burden of osmoregulation, dietary salt inclusion can alleviate the negative impacts of low-saline waters in several aquaculture species. This study investigated the effects of increasing dietary salt levels on the growth, feed utilization, body composition, and tissue fatty acid composition of juvenile turbot (initial live weight 120.3 ± 0.03 g/fish). Fish were fed five experimental diets supplemented with varying levels of sodium chloride (1.8-6.4%) or a control diet without salt. Each diet was tested in triplicate tanks for 9 weeks. Results showed that increasing dietary salt intake negatively impacted turbot performance, with significant reductions in weight gain, specific growth rate, and feed conversion ratio. Dry matter and ash content in the whole body and filet increased quadratically with increasing salt levels, whereas gill moisture and protein content decreased linearly. Furthermore, the nitrogen, lipid, and energy utilization efficiencies decreased with their respective intake and gain levels. Dietary salt significantly influenced the fatty acid profiles of gill, liver, and filet tissues. In the gill, monounsaturated fatty acids (16:1n-7, ΣMUFA) and n-6 PUFA (20:2n-6) increased, whereas EPA and DHA decreased. Liver ΣSFA (16:0, 18:0) increased, and n-3 PUFA (18:3n-3, 20:5n-3) decreased with increasing dietary salt. Filet saturated fatty acids (14:0, 15:0, 17:0) and n-6 PUFA (20:2n-6, 20:4n-6) increased, while n-3 PUFA (18:3n-3, EPA) decreased with dietary salt. DHA levels in filets showed a quadratic increase. Overall, this study shows that increasing dietary salt negatively impacts turbot growth, feed utilization, and tissue fatty acid composition in brackish water, highlighting the need for further studies on salinity management strategies for turbot aquaculture.

Exploring the impact of high salinity and parasite infection on antioxidant and immune systems in Coris julis in the Pityusic Islands (Spain)

Climate change associated with human activities alters marine ecosystems and causes imbalances and abrupt changes in sea conditions. Scarce freshwater resources for human consumption often prompt the construction of desalination plants, which discharge significant amounts of brine into the sea, potentially elevating salinity levels. Furthermore, global trade together with higher temperature and pollution can facilitate the spread of parasites. The aim of this study was to assess the potential effects of salinity, an abiotic stressor, and Scaphanocephalus sp. parasitic infection responsible for black spot disease, a biotic stressor, on Coris julis, a common fish in the Balearic Islands (Spain). Fish were sampled from an area affected by a desalination plant, one with a high rate of parasite infection and a control area, and biomarkers were analysed in the liver, gills and epithelial mucosa. Both salinity and the parasite induced increases in catalase (CAT) and glutathione s-transferase activities in the liver, while superoxide dismutase (SOD) did not show significant changes. The effects of salinity were evident to a greater extent in the gills with an increase in the activity of all enzymes, as well as in the production of reactive species. The effects of the parasite were mainly observed in the mucus with significant increases in CAT and SOD activities. Regarding immune response markers in the mucus, both stressors induced an increase in lysozyme and alkaline phosphatase activities, and in the case of the parasite, also an increase in immunoglobulins. Malondialdehyde, as an indicator of oxidative damage, remained unchanged. In conclusion, both abiotic and abiotic stress induce a stress situation in C. julis that responds by activating its antioxidant and immune defence mechanisms but does cause oxidative damage. The differential tissue response to different stressors highlights the value of analysing multiple tissues to detect early indicators of diverse impacts on marine fauna.

Tissue-specific effects of temperature and salinity on the cell cycle and apoptosis in the Nile Tilapia (Oreochromis niloticus)

The Nile Tilapia (Oreochromis niloticus) evolved in warm, freshwater rivers, but possesses a broad physiological tolerance to a range of environmental conditions. Due to this hardiness and resilience, this species has been successfully introduced to regions widely outside of its native range. Here, we examine the impact of temperature and salinity variation on this species at the sub-lethal level. Specifically, Nile Tilapia were exposed to two temperatures (21 °C or 14 °C) and three salinities (0, 16, 34 ppt) for 1-h. Given their native habitat, the 21 °C / 0 ppt exposure was considered the control condition. Both cell cycle arrest and apoptosis represent sub-lethal but deleterious responses to environmental stress. Flow cytometry was used to assess the percentage of cells in a given stage of the cell cycle as a metric of cell cycle arrest in spleen and liver. Percentage of apoptotic cells were also quantified. Spleen was more sensitive to cold stress, demonstrating an increase in cells in the G2/M phase after experimental treatment. Liver, however, was more sensitive to salinity stress, with a significant increase in cells stalled in G2/M phase at higher salinities, which is in keeping with the freshwater evolutionary history of the species. A modest apoptotic signal was observed in liver but not in spleen. Together, these findings demonstrate that even short, acute exposures to cold temperatures and elevated salinity can cause sub-lethal damage in a species that is otherwise tolerant of environmental stress at the whole organism level.

Unveiling osmoregulation and immunological adaptations in Eleutheronema tetradactylum gills through high-throughput single-cell transcriptome sequencing

The fourfinger threadfin fish (Eleutheronema tetradactylum) is an economically significant species renowned for its ability to adapt to varying salinity environments, with gills serving as their primary organs for osmoregulation and immune defense. Previous studies focused on tissue and morphological levels, whereas ignored the cellular heterogeneity and the crucial gene information related to core cell subsets within E. tetradactylum gills. In this study, we utilized high-throughput single-cell RNA sequencing (scRNA-seq) to analyze the gills of E. tetradactylum, characterizing 16 distinct cell types and identifying unique gene markers and enriched functions associated within each cell type. Additionally, we subdivided ionocyte cells into four distinct subpopulations for the first time in E. tetradactylum gills. By employing weighted gene co-expression network analysis (WGCNA), we further investigated the cellular heterogeneity and specific response mechanisms to salinity fluctuant. Our findings revealed the intricate osmoregulation and immune functions of gill cells, highlighting their crucial roles in maintaining homeostasis and adapting to fluctuating salinity levels. This comprehensive cell-type atlas provides valuable insights into the species adaptive strategies, contributing to the conservation and management of this commercially significant fish as well as other euryhaline species.

Persistent interactive effects of developmental salinity and temperature in Atlantic killifish (Fundulus heteroclitus)

Climate change alters multiple abiotic environmental factors in aquatic environments but relatively little is known about their interacting impacts, particularly in developing organisms where these exposures have the potential to cause long-lasting effects. To explore these issues, we exposed developing killifish embryos (Fundulus heteroclitus) to 26 °C or 20 °C and 20 ppt or 3 ppt salinity in a fully-factorial design. After hatching, fish were transferred to common conditions of 20 °C and 20 ppt to assess the potential for persistent developmental plasticity. Warm temperature increased hatching success and decreased hatch time, whereas low salinity negatively affected hatching success, but this was only significant in fish developed at 20 °C. Temperature, salinity, or their interaction affected mRNA levels of genes typically associated with thermal and hypoxia tolerance (hif1a, hsp90b, hsp90a, hsc70, and hsp70.2) across multiple developmental timepoints. These differences were persistent into the juvenile stage, where the fish that developed at 26 °C had higher expression of hif1a, hsp90b, hsp90a, and hsp70.2 than fish developed at 20 °C, and this was particularly evident for the group developed at both high temperature and salinity. There were also long-lasting effects of developmental treatments on body size after four months of rearing under common conditions. Fish developed at low salinity or temperature were larger than fish developed at high temperature or salinity, but there was no interaction between the two factors. These data highlight the complex nature of the developmental effects of interacting stressors which has important implications for predicting the resilience of fishes in the context of climate change.

Control of fluid intake in dehydrated rats and evolution of sodium appetite

The objective of the present work is to examine from a new perspective the existence of causal factors not predicted by the classical theory that thirst and sodium appetite are two distinct motivations. For example, we ask why water deprivation induces sodium appetite, thirst is not "water appetite", and intracellular dehydration potentially causes sodium appetite. Contrary to the classical theory, we suggest that thirst first, and sodium appetite second, designate a temporal sequence underlying the same motivation. The single motivation becomes an "intervenient variable" a concept borrowed from the literature, fully explained in the text, between causes of dehydration (extracellular, intracellular, or both together), and respective behavioral responses subserved by hindbrain-dependent inhibition (e.g., lateral parabrachial nucleus) and forebrain facilitation (e.g., angiotensin II). A corollary is homology between rat sodium appetite and marine teleost thirst-like motivation that we name "protodipsia". The homology argument rests on similarities between behavior (salty water intake) and respective neuroanatomical as well as functional mechanisms. Tetrapod origin in a marine environment provides additional support for the homology. The single motivation hypothesis is also consistent with ingestive behaviors in nature given similarities (e.g., thirst producing brackish water intake) between the behavior of the laboratory rat and wild animals, rodents included. The hypotheses of single motivation and homology might explain why hyperosmotic rats, or eventually any other hyperosmotic tetrapod, shows paradoxical signs of sodium appetite. They might also explain how ingestive behaviors determined by dehydration and subserved by hindbrain inhibitory mechanisms contributed to tetrapod transition from sea to land.

Interactive effects of temperature and salinity on metabolism and activity of the copepod Tigriopus californicus

In natural environments, two or more abiotic parameters often vary simultaneously, and interactions between co-varying parameters frequently result in unpredictable, non-additive biological responses. To better understand the mechanisms and consequences of interactions between multiple stressors, it is important to study their effects on not only fitness (survival and reproduction) but also performance and intermediary physiological processes. The splash-pool copepod Tigriopus californicus tolerates extremely variable abiotic conditions and exhibits a non-additive, antagonistic interaction resulting in higher survival when simultaneously exposed to high salinity and acute heat stress. Here, we investigated the response of T. californicus in activity and oxygen consumption under simultaneous manipulation of salinity and temperature to identify whether this interaction also arises in these sublethal measures of performance. Oxygen consumption and activity rates decreased with increasing assay salinity. Oxygen consumption also sharply increased in response to acute transfer to lower salinities, an effect that was absent upon transfer to higher salinities. Elevated temperature led to reduced rates of activity overall, resulting in no discernible impact of increased temperature on routine metabolic rates. This suggests that swimming activity has a non-negligible effect on the metabolic rates of copepods and must be accounted for in metabolic studies. Temperature also interacted with assay salinity to affect activity, and with acclimation salinity to affect routine metabolic rates upon acute salinity transfer, implying that the sublethal impacts of these co-varying factors are also not predictable from experiments that study them in isolation.

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.

Structure and gene expression changes of the gill and liver in juvenile black porgy (Acanthopagrus schlegelii) under different salinities

Black porgy (Acanthopagrus schlegelii) is an important marine aquaculture species in China. It is an ideal object for the cultivation of low-salinity aquaculture strains in marine fish and the study of salinity tolerance mechanisms in fish because of its strong low-salinity tolerance ability. Gill is the main osmoregulatory organ in fish, and the liver plays an important role in the adaptation of the organism to stressful environments. In order to understand the coping mechanisms of the gills and livers of black porgy in different salinity environments, this study explored these organs after 30 days of culture in hypoosmotic (0.5 ppt), isosmotic (12 ppt), and normal seawater (28 ppt) at histologic, physiologic, and transcriptomic levels. The findings indicated that gill exhibited a higher number of differentially expressed genes than the liver, emphasizing the gill's heightened sensitivity to salinity changes. Protein interaction networks and enrichment analyses highlighted energy metabolism as a key regulatory focus at both 0.5 ppt and 12 ppt salinity in gills. Additionally, gills showed enrichment in ions, substance transport, and other metabolic pathways, suggesting a more direct regulatory response to salinity stress. The liver's regulatory patterns at different salinities exhibited significant distinctions, with pathways and genes related to metabolism, immunity, and antioxidants predominantly activated at 0.5 ppt, and molecular processes linked to cell proliferation taking precedence at 12 ppt salinity. Furthermore, the study revealed a reduction in the volume of the interlamellar cell mass (ILCM) of the gills, enhancing the contact area of the gill lamellae with water. At 0.5 ppt salinity, hepatic antioxidant enzyme activity increased, accompanied by oxidative stress damage. Conversely, at 12 ppt salinity, gill NKA activity significantly decreased without notable changes in liver structure. These results underscore the profound impact of salinity on gill structure and function, highlighting the crucial role of the liver in adapting to salinity environments.

Assessing the water quality in a World Heritage Site using biomarkers in top fish predators

The use of biomarkers in fish for biomonitoring is a valuable approach to reveal effects of human impacts on biota health. Top predator fish are effective models for monitoring human activities' impacts on aquatic ecosystems. The Guaraguaçu River is the largest river-system on coastal region of South Brazil and a World Heritage site. The river receives contaminants from disorderly urban growth, including discharges of domestic sewage and small fishery boats, particularly during the tourist season. Our study aimed to assess impact of anthropogenic activities on water quality in the Guaraguaçu River by analyzing environmental contamination biomarkers in the top fish predator Hoplias malabaricus. Fish were collected using a fyke net trap across sectors representing a gradient of anthropic impact: sector 1 - pristine; sector 2 - impacted; and sector 3 - less impacted. Water samples were collected to analyze the presence of trace elements and pesticide. Biomarkers of the antioxidant system, histopathology, genotoxicity, neurotoxicity, and concentration of trace elements were analyzed in fish tissues. In water samples Al, Fe and Mn were detected, but no pesticides were found. In fish muscle, zinc and iron were detected. Brain acetylcholinesterase activity decreased in impacted sectors, indicating neurotoxic effects. The antioxidant system increased activity in gills and liver, and damage from lipoperoxidation was observed, particularly in sector 2 when compared to sector 1, suggesting oxidative stress. Histopathological biomarkers revealed lesions in the liver and gills of fish in impacted sectors. Micronuclei, a genotoxicity biomarker, were observed in organisms from all sectors. Our results demonstrate detrimental effects of poor water quality on biota health, even when contaminants are not detected in water.

Effects of different salinity reduction intervals on osmoregulation, anti-oxidation and apoptosis of Eriocheir sinensis megalopa

Eriocheir sinensis megalopa has a special life history of migrating from seawater to freshwater. In order to investigate how the megalopa adapt themselves to the freshwater environment, we designed an experiment to reduce the salinity of water from 30 ppt to 0 at rates of 30 ppt, 15 ppt, 10 ppt, and 5 ppt per 24 h to evaluate the effects of different degrees of hyposaline stress on the osmotic regulation ability and antioxidant system of the megalopa. Experimental results related to osmotic pressure regulation show that the gill tissue of megalopa in the treatment group of 30 ppt/24 h rapid reduction of salinity was damaged, while in the treatment group of 5 ppt/24 h it was intact. At the same time, the experiment also found that in each treatment group with different salinity reduction rates, compared with the control salinity, the NKA activity of megalopa increased significantly after the salinity was reduced to 20 ppt (p < 0.05). In addition, two genes involved in chloride ion transmembrane absorption have different expression patterns in the treatment groups with different salinity reduction rates. Among them, Clcn2 was significantly highly expressed only in the rapid salinity reduction intervals of 30 ppt/24 h and 15 ppt/24 h (p < 0.05). Slc26a6 was significantly highly expressed only in the slow salinity reduction intervals of 10 ppt/24 h and 5 ppt/24 h (p < 0.05). On the other hand, the results of antioxidant and apoptosis related experiments showed that in all treatment groups with different rates of salinity reduction, the activities of T-AOC, GSH-PX, and CAT basically increased significantly after salinity reduction compared to the control salinity. Moreover, the activities of T-AOC and CAT were significantly higher in the 10 ppt/24 h and 5 ppt/24 h treatment groups than in the 30 ppt/24 h and 15 ppt/24 h treatment groups. Finally, the experimental results related to apoptosis showed that the expression trends of Capase3 and Bax-2 were basically the same in the treatment groups with different salinity reduction rates, and their expressions were significantly higher in the 10 ppt/24 h and 5 ppt/24 h treatment groups than in the 30 ppt/24 h and 15 ppt/24 h treatment groups. In summary, the present study found that megalopa had strong hyposaline tolerance and were able to regulate osmolality at different rates of salinity reduction, but the antioxidant capacity differed significantly between treatment groups, with rapid salinity reduction leading to oxidative damage in the anterior gills and reduced antioxidant enzyme activity and apoptosis levels.

Mitigation of haemato-genotoxic and stress response effects in Cyprinus carpio via silymarin dietary supplementation following deltamethrin exposure

The study examined the potential of Silymarin, a blend of bioactive flavonolignans extracted from the milk thistle Silybum marianum, to mitigate Deltamethrin-induced toxicity in the blood of Cyprinus carpio. Fish were exposed to Deltamethrin (0.66 μg/L), the plant extract, or a combination of both for a duration of thirty days. Various parameters, including serum biochemical markers, erythrocytic abnormalities, and genotoxicity endpoints, were assessed. Results indicated a significant (p < 0.05) increase in the levels of AST, ALT, ALP, blood urea nitrogen, creatinine, glucose, cholesterol, and TLC in the fish exposed to the pesticide. Conversely, total protein, TEC, and Hb showed a notable decrease. There was also a notable rise in micronuclei and erythrocytic abnormalities such as acanthocytes, microcytes, and notched cells. Under ultrastructural examination, phenotypic deformities like spherocytosis, discocytes, and clumped erythrocytes were observed. However, dietary supplementation of silymarin (1 g/kg) significantly restored the biochemical, genetic, and cellular parameters, resembling those of the control group. This suggests the potential of this plant extract in protecting the common carp, Cyprinus carpio, from Deltamethrin-induced damage by scavenging free radicals and reducing DNA oxidative stress.

Study on the osmotic response and function of myo-inositol oxygenase in euryhaline fish nile tilapia (Oreochromis niloticus)

To understand the role of myo-inositol oxygenase (miox) in the osmotic regulation of Nile tilapia, its expression was analyzed in various tissues. The results showed that the expression of miox gene was highest in the kidney, followed by the liver, and was significantly upregulated in the kidney and liver under 1 h hyperosmotic stress. The relative luminescence efficiency of the miox gene transcription starting site (-4,617 to +312 bp) under hyperosmotic stress was measured. Two fragments (-1,640/-1,619 and -620/-599) could induce the luminescence activity. Moreover, the -1,640/-1,619 and -620/-599 responded to hyperosmotic stress and high-glucose stimulation by base mutation, suggesting that osmotic and carbohydrate response elements may exist in this region. Finally, the salinity tolerance of Nile tilapia was significantly reduced after the knocking down of miox gene. The accumulation of myo-inositol was affected, and the expression of enzymes in glucose metabolism was significantly reduced after the miox gene was knocked down. Furthermore, hyperosmotic stress can cause oxidative stress, and MIOX may help maintain the cell redox balance under hyperosmotic stress. In summary, MIOX is essential in osmotic regulation to enhance the salinity tolerance of Nile tilapia by affecting myo-inositol accumulation, glucose metabolism, and antioxidant performance.NEW & NOTEWORTHY Myo-inositol oxygenase (MIOX) is the rate-limiting enzyme that catalyzes the first step of MI metabolism and determines MI content in aquatic animals. To understand the role of miox in the osmotic regulation of Nile tilapia, we analyzed its expression in different tissues and its function under hyperosmotic stress. This study showed that miox is essential in osmotic regulation to enhance the salinity tolerance of Nile tilapia by affecting myo-inositol accumulation, glucose metabolism, and antioxidant performance.

Comparative proteomic profiling represents an inhibition of protein synthesis to regulate osmotic stress in Nile tilapia (Oreochromis niloticus) embryos

Seawater (SW)-acclimated Nile tilapia, Oreochromis niloticus, can tolerate up to 30 g.L-1 SW but rarely produce offspring. The embryos of SW-acclimated O. niloticus survived equally well from 0- to 10-g.L-1 environment but not under 20-g. L-1. However, when the embryos were incubated under 10 g.L-1 during days 0-3, and then the salinity was suddenly shifted to and maintained at 20 g.L-1 during days 4-6, their survival rate was comparable to those incubated under 0 and 10 g.L-1. To elucidate a molecular adaptation of the embryos that survived different salinity environments, the proteomic profiles of the newly hatched embryos, or early larvae, hatched under 0 g.L-1, 10 g.L-1, and those being incubated at 10 g.L-1 during days 0-3 followed at 20 g.L-1 during days 4-6 were compared. Total proteins extracted from the samples were identified with a gel-free shot-gun proteomics approach using the Nile tilapia protein database. The early larvae from the three groups expressed 2295 proteins, and 279 proteins showed statistically different expressions among groups. Downregulation of the 182 proteins in the larvae hatched under 10 and 20 g.L-1 was found to include 22 proteins that are responsible for cellular responses to osmotic stress. This adaptation may be a crucial factor in reducing cellular metabolism and ion transport between the intra- and extra-cellular environment to stabilize cellular osmolality. In addition, some of these proteins suppress cellular damage from oxygen free radicals generated from the osmotic stress. Eighty-seven proteins significantly changed in the larvae hatched under 20 g.L-1 were clustered. Nineteen of the cellular stress response proteins, which were considered to be mortality induction, were described.

Effects of Erythromycin on Nereis succinea and the Intestinal Microbiome across Different Salinity Levels

The exposure of aquatic organisms to pollutants often occurs concomitantly with salinity fluctuations. Here, we reported the effects of erythromycin (0.250, 7.21, and 1030 μg/L) on marine invertebrate N. succinea and its intestinal microbiome under varying salinity levels (5‰, 15‰, and 30‰). The salinity elicited significant effects on the growth and intestinal microbiome of N. succinea. The susceptibility of the intestinal microbiome to erythromycin increased by 8.7- and 6.2-fold at salinities of 15‰ and 30‰, respectively, compared with that at 5‰ salinity. Erythromycin caused oxidative stress and histological changes in N. succinea intestines, and inhibited N. succinea growth in a concentration-dependent manner under 30‰ salinity with a maximum inhibition of 25%. At the intestinal microbial level, erythromycin enhanced the total cell counts at 5‰ salinity but reduced them at 15‰ salinity. Under all tested salinities, erythromycin diminished the antibiotic susceptibility of the intestinal microbiome. Two-way ANOVA revealed significant interactive effects (p < 0.05) between salinity and erythromycin on various parameters, including antibiotic susceptibility and intestinal microbial diversity. The present findings demonstrated the significant role of salinity in modulating the impacts of erythromycin, emphasizing the necessity to incorporate salinity fluctuations into environmental risk assessments.

Variations of salinity during reproduction and development affect ontogenetic trajectories in a coastal amphibian

Although coastal ecosystems are naturally submitted to temporal variations of salinity, salinization has been increasing over time threatening coastal biodiversity. Species that exploit such habitats can thus be exposed to brackish water at different life stages. However, the impacts of variations of salinity on wildlife remain poorly understood. This is particularly true for coastal amphibians, due to the strong dependency of early life stages (embryos and larvae) on aquatic environments. In order to investigate the effect of salinity during egg laying and embryonic and larval development of coastal amphibians, we used a full-factorial design to expose reproductive adults, eggs, and larvae of coastal spined toads (Bufo spinosus) to fresh (0 g.l-1) or brackish water (4 g.l-1). At egg laying, we evaluated parental investment in reproduction. During embryonic and larval development, we assessed effects on survival, development, and growth. We highlighted strong effects of environmental salinity on reproduction (reduced egg laying time, marginally reduced egg size, and reduced investment in reproduction). Responses to salinity were highly dependent on the developmental stages of exposure (stronger effects when individuals were exposed during embryonic development). These effects carried over when exposure occurred at egg laying or during embryonic development, highlighting the importance of the environmental conditions during early life on ontogenetic trajectories. We also highlighted partial compensation when individuals were transferred back to freshwater. Whether the magnitude of these responses can allow coastal biodiversity to overcome the observed detrimental effects of salinization remain to be assessed.

Diverse Transcriptome Responses to Salinity Change in Atlantic Cod Subpopulations

Adaptation to environmental variation caused by global climate change is a significant aspect of fisheries management and ecology. A reduction in ocean salinity is visible in near-shore areas, especially in the Baltic Sea, where it is affecting the Atlantic cod population. Cod is one of the most significant teleost species, with high ecological and economical value worldwide. The population of cod in the Baltic Sea has been traditionally divided into two subpopulations (western and eastern) existing in higher- and lower-salinity waters, respectively. In recent decades, both Baltic cod subpopulations have declined massively. One of the reasons for the poor condition of cod in the Baltic Sea is environmental factors, including salinity. Thus, in this study, an oligonucleotide microarray was applied to explore differences between Baltic cod subpopulations in response to salinity fluctuations. For this purpose, an exposure experiment was conducted consisting of salinity elevation and reduction, and gene expression was measured in gill tissue. We found 400 differentially expressed genes (DEGs) involved in the immune response, metabolism, programmed cell death, cytoskeleton, and extracellular matrix that showed a subpopulation-dependent pattern. These findings indicate that osmoregulation in Baltic cod is a complex process, and that western and eastern Baltic cod subpopulations respond differently to salinity changes.

Comparative Transcriptome and WGCNA Analysis Reveal Molecular Responses to Salinity Change in Larvae of the Iwagaki Oyster Crassostrea Nippona

The Iwagaki oyster Crassostrea nippona is an important aquaculture species with significant potential for large-scale oyster farming. It is susceptible to the fluctuated salinity in the coastal area. In this study, we compared the transcriptome of Crassostrea nippona larvae under variant conditions with low-salinity stress (28, 20, 15, 10, and 5 practical salinity units (psu)) for 24 h. KEGG enrichment analysis of differentially expressed genes (DEGs) from pairwise comparisons identified several free amino acid metabolism pathway (taurine and hypotaurine, arginine and proline, glycine, and beta-alanine) contributing to the salinity change adaptation and activated "lysosome" and "apoptosis" pathway in response to the low-salinity stress (10 and 5 psu). Trend analysis revealed sustained upregulation of transmembrane transport-related genes (such as SLC family) and downregulation of ribosomal protein synthesis genes faced with decreasing salinities. In addition, 9 biomarkers in response to low-salinity stress were identified through weighted gene co-expression network analysis (WGCNA) and validated by qRT-PCR. Our transcriptome analysis provides a comprehensive view of the molecular mechanisms and regulatory networks underlying the adaptive responses of oyster larvae to hypo-salinity conditions. These findings contribute to our understanding of the complex biological processes involved in oyster resilience and adaptation to changing environmental conditions.

Effect of photoperiod on serum biochemistry, electrolytic balance, acute phase response and histopathology of butter catfish, Ompok bimaculatus (Bloch, 1794)

The present study was executed to evaluate the effect of photoperiod on serum biochemical parameters (glucose, cortisol, ALT, AST and LDH), electrolytic balance (Sodium and potassium), acute phase response (CRP) and histopathology (liver, kidney and skin) of an endangered high valued catfish, Ompok bimaculatus. Catfish (21.00 ± 1.53 cm and 30.00 ± 2.31 g) from the acclimatized stock were randomly distributed to six 120 × 45 × 60 cm3 FRP tanks (n = 20 fish per tank) and exposed to 1500 lx light intensity under different photoperiods [24:0 light: dark (L: D), 15L: 9D, 12L: 12D, 9L: 15D, 0L: 24D and a natural photoperiod (control)], and fed at a daily rate of 2% of bodyweight, twice a day for 60 days. Serum glucose, cortisol and enzymes including aspartate transaminase (AST), lactate dehydrogenase (LDH), alanine transaminase (ALT), and acute phase reactant, such as C-reactive protein (CRP) increased significantly (P < 0.05) in continuous light (24L: 0D), continuous dark (0L: 24D) and short day (9L: 15D) photoperiods, whereas in 15L: 9D and 12L:12D photoperiods, those were in decreasing trend. Serum electrolytes, i.e. potassium level was elevated and sodium level was declined in 24L: 0D, 0L: 24D and 9L: 15D photoperiod groups. Moreover, significant histological alterations in the liver, kidney and skin tissue were also evidenced in the experimented catfish. Typical polygonal hepatocytes with normal blood vessels in liver and normal organization of kidney were seen in catfish of 15L: 9D group. Histological analysis of other groups displayed nuclear degeneration, karyorrhexis, karyolysis, melanomacrophages, nuclear hypertrophy, sinusoid dilation and vacuolar degeneration in liver and hyaline droplets accumulation, granular degeneration, fragmentation of glomerulus and focal necrosis of epithelial cells in kidney. Additionally, general structure of the skin was observed in control group as well as in 15L: 9D group. Contrarily, in 24L: 0D group increased number of mucous cells and vacuoles was observed in the skin of butter catfish. In 9L: 15D and 0L: 24D photoperiods, O. bimaculatus exhibited ruptured epithelial cells, enlarged alarm cells, fat cells, necrotic cells and vacuoles in the skin tissue. The present study depicted that 15L: 9D photoperiod can induce better health of catfish, O. bimaculatus, which, in turn, can help farmers to increase the production of this high valued catfish in future.

Growth retardation and suppression of ubiquitin-dependent catabolic processes in the brackish water clam Corbicula japonica in response to salinity changes and bioaccumulation of toxic heavy metals

The brackish water clam (Corbicula japonica) is constantly exposed to stressful salinity gradients and high levels of heavy metals in the freshwater-saltwater interface of estuary environments, which are introduced from upstream regions and land. To identify the key molecular pathways involved in the response to salinity changes and heavy metal bioaccumulation, we obtained the transcriptomes of C. japonica inhabiting different salinities and heavy metal distributions in Gwangyang Bay (Korea) using RNA sequencing. Among a total of 404,486 assembled unigenes, 5534 differentially expressed genes were identified in C. japonica inhabiting different conditions, 1549 of which were significantly upregulated and 1355 were significantly downregulated. Correlation analyses revealed distinct gene expression patterns between the low and high conditions of salinity and heavy metal bioaccumulation. Functional annotation revealed significant downregulation of genes involved in "ubiquitin-dependent protein catabolic process," "tricarboxylic acid cycle," and "intracellular protein transport" in C. japonica from the high condition compared to the low condition. Transcription and translation pathways were significantly enriched in the high condition. Additionally, upon comparison of the low and high conditions by qRT-PCR and proteasome enzyme activity analyses, our findings demonstrated that environmental stress could suppress the ubiquitin-proteasome complex (UPC). Additionally, transcriptomic changes under high salinity stress conditions may be related to an increase in cellular protection by defense enzymes, which leads to more energy being required and a disruption of energy homeostasis. Ultimately, this could cause growth retardation in the clam C. japonica. In summary, this study provides the first evidence of UPC suppression induced by a combination of high salinity and heavy metal bioaccumulation stress in C. japonica, which could compromise the survival and growth of estuarine bivalves.

Long-term trends of salinity in coastal wetlands: Effects of climate, extreme weather events, and sea water level

Coastal freshwater ecosystems play major roles as reservoirs of biodiversity and provide many ecosystem services and protection from extreme weather events. While they are of particular importance worldwide, they are affected by a large variety of anthropogenic threats, among which salinization has been less studied, particularly regarding large temporal and spatial data sets based on real case scenarios, while salinity can impact biodiversity and ecosystem functioning. In this study, we investigated the variations of salinity across long-term (1996-2020) and seasonal (monthly records) temporal scales and spatial (varying distance to the coastline) scales in water bodies of two typical temperate coastal wetlands situated on the Atlantic coast of France. We complemented our analyses with models of sea water levels computed at both sites across 2000-2020. Our detailed data set allowed for highlighting that salinity in ponds varied seasonally (higher during summer, due to decreased precipitation and higher temperature), but also spatially (higher closer to the seashore, which pattern increased through time). Over the long term, decreased precipitation but not increased temperature induced increasing salinity. We also highlighted contrasted long-term patterns of salinity changes on these two coastal wetlands, with one site were salinity decreased over time linked to the responses to marine flood, allowing to document the temporal dynamics of salinity following a massive intrusion of sea water. Complementarily, at both sites, water levels at high tides increased through time, a pattern which can induce additional salinization. To our knowledge, our study is the first to investigate long-term changes in salinity in coastal wetlands through natural processes (e.g. seaspray, seasonal variations) and ongoing climate perturbations (e.g. marine surges linked to extreme weather events, increased temperature and decreased precipitations).

Effects of β-1,3-glucan on growth, immune responses, and intestinal microflora of the river prawn (Macrobrachium nipponense) and its resistance against Vibrio parahaemolyticus

In this study, we investigated the impact of β-1,3-glucan on the immune responses and gut microbiota of the river prawn (Macrobrachium nipponense) in the presence of Vibrio parahaemolyticus stress. Shrimps were fed one of the following diets: control (G1), 0.2% curdlan (G2), 0.1% β-1,3-glucan (G3), 0.2% β-1,3-glucan (G4), or 1.0% β-1,3-glucan (G5) for 6 weeks and then challenged with V. parahaemolyticus for 96 h. Under Vibrio stress, shrimps in G4 exhibited the highest length gain rate, weight gain rate, and survival rate. They also showed increased intestinal muscle thickness and villus thickness compared to the control and 0.2% curdlan groups. The apoptosis rate was lower in G4 than in the control group, and the digestive enzyme activities (pepsin, trypsin, amylase, and lipase), immune enzyme activities (acid phosphatase, alkaline phosphatase, lysozyme, and phenoxidase), and energy metabolism (triglyceride, cholesterol, glycogen, and lactate dehydrogenase) were enhanced. Expression levels of growth-related genes (ecdysone receptor, calmodulin-dependent protein kinase I, chitin synthase, and retinoid X receptor) and immune-related genes (toll-like receptor 3, myeloid differentiation primary response 88, mitogen-activated protein kinase 7, and mitogen-activated protein kinase 14) were higher in G4 than in the control. Microbiota analysis indicated higher bacterial abundance in shrimps fed β-1,3-glucan, as evidenced by Sob, Chao1, and ACE indices. Moreover, 0.2% β-1,3-glucan increased the relative abundances of Bacteroidota and Firmicutes while reducing those of Corynebacteriales and Lactobacillales. In summary, β-1,3-glucan enhances immune enzyme activities, alters immune-related gene expression, and impacts gut microbial diversity in shrimp. These findings provide valuable insights into the mechanisms underlying β-1,3 glucan's immune-enhancing effects.

Algal Bio-Stimulants Enhance Salt Tolerance in Common Bean: Dissecting Morphological, Physiological, and Genetic Mechanisms for Stress Adaptation

Salinity adversely affects the plant's morphological characteristics, but the utilization of aqueous algal extracts (AE) ameliorates this negative impact. In this study, the application of AE derived from Chlorella vulgaris and Dunaliella salina strains effectively reversed the decline in biomass allocation and water relations, both in normal and salt-stressed conditions. The simultaneous application of both extracts in salt-affected soil notably enhanced key parameters, such as chlorophyll content (15%), carotene content (1%), photosynthesis (25%), stomatal conductance (7%), and transpiration rate (23%), surpassing those observed in the application of both AE in salt-affected as compared to salinity stress control. Moreover, the AE treatments effectively mitigated lipid peroxidation and electrolyte leakage induced by salinity stress. The application of AE led to an increase in GB (6%) and the total concentration of free amino acids (47%) by comparing with salt-affected control. Additionally, salinity stress resulted in an elevation of antioxidant enzyme activities, including superoxide dismutase, ascorbate peroxidase, catalase, and glutathione reductase. Notably, the AE treatments significantly boosted the activity of these antioxidant enzymes under salinity conditions. Furthermore, salinity reduced mineral contents, but the application of AE effectively counteracted this decline, leading to increased mineral levels. In conclusion, the application of aqueous algal extracts, specifically those obtained from Chlorella vulgaris and Dunaliella salina strains, demonstrated significant efficacy in alleviating salinity-induced stress in Phaseolus vulgaris plants.

Microbial community changes correlate with impaired host fitness of Aurelia aurita after environmental challenge

Climate change globally endangers certain marine species, but at the same time, such changes may promote species that can tolerate and adapt to varying environmental conditions. Such acclimatization can be accompanied or possibly even be enabled by a host's microbiome; however, few studies have so far directly addressed this process. Here we show that acute, individual rises in seawater temperature and salinity to sub-lethal levels diminished host fitness of the benthic Aurelia aurita polyp, demonstrated by up to 34% reduced survival rate, shrinking of the animals, and almost halted asexual reproduction. Changes in the fitness of the polyps to environmental stressors coincided with microbiome changes, mainly within the phyla Proteobacteria and Bacteroidota. The absence of bacteria amplified these effects, pointing to the benefit of a balanced microbiota to cope with a changing environment. In a future ocean scenario, mimicked by a combined but milder rise of temperature and salinity, the fitness of polyps was severely less impaired, together with condition-specific changes in the microbiome composition. Our results show that the effects on host fitness correlate with the strength of environmental stress, while salt-conveyed thermotolerance might be involved. Further, a specific, balanced microbiome of A. aurita polyps supports the host's acclimatization. Microbiomes may provide a means for acclimatization, and microbiome flexibility can be a fundamental strategy for marine animals to adapt to future ocean scenarios and maintain biodiversity and ecosystem functioning.

Decolorization of reactive azo dye using novel halotolerant yeast consortium HYC and proposed degradation pathway

The presence of high salinity levels in textile wastewater poses a significant obstacle to the process of decolorizing azo dyes. The present study involved the construction of a yeast consortium HYC, which is halotolerant and was recently isolated from wood-feeding termites. The consortium HYC was mainly comprised of Sterigmatomyces halophilus SSA-1575 and Meyerozyma guilliermondii SSA-1547. The developed consortium demonstrated a decolourization efficiency of 96.1% when exposed to a concentration of 50 mg/l of Reactive Black 5 (RB5). The HYC consortium significantly decolorized RB5 up to concentrations of 400 mg/l and in the presence of NaCl up to 50 g/l. The effects of physicochemical factors and the degradation pathway were systematically investigated. The optimal pH, salinity, temperature, and initial dye concentration were 7.0, 3%, 35 °C and 50 mg/l, respectively. The co-carbon source was found to be essential, and the addition of glucose resulted in a 93% decolorization of 50 mg/l RB5. The enzymatic activity of various oxido-reductases was assessed, revealing that NADH-DCIP reductase and azo reductase exhibited greater activity in comparison to other enzymes. UV-Visible (UV-vis) spectrophotometry, Fourier-transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC), and gas chromatography-mass spectrometry (GC-MS) were utilized to identify the metabolites generated during the degradation of RB5. Subsequently, a metabolic pathway was proposed. The confirmation of degradation was established through alterations in the functional groups and modifications in molecular weight. The findings indicate that this halotolerant yeast consortium exhibits promising potential of degrading dye compounds. The results of this study offer significant theoretical basis and crucial perspectives for the implementation of halotolerant yeast consortia in the bioremediation of textile and hypersaline wastewater. This approach is particularly noteworthy as it does not produce aromatic amines.

Interplay of gene expression and regulators under salinity stress in gill of Labeo rohita

BACKGROUND

Labeo rohita is the most preferred freshwater carp species in India. The concern of increasing salinity concentration in freshwater bodies due to climate change may greatly impact the aquatic environment. Gills are one of the important osmoregulatory organs and have direct contact with external environment. Hence, the current study is conducted to understand the gill transcriptomic response of L. rohita under hypersalinity environment.

RESULTS

Comprehensive analysis of differentially expressed long non-coding RNAs (lncRNAs), microRNAs (miRNAs) and mRNAs was performed in gills of L. rohita treated with 2, 4, 6 and 8ppt salinity concentrations. Networks of lncRNA-miRNA-mRNA revealed involvement of 20, 33, 52 and 61 differentially expressed lncRNAs, 11, 13, 26 and 21 differentially expressed miRNAs in 2, 4, 6 and 8ppt groups between control and treatment respectively. These lncRNA-miRNA pairs were regulating 87, 214, 499 and 435 differentially expressed mRNAs (DE mRNAs) in 2, 4, 6 and 8ppt treatments respectively. Functional analysis of these genes showed enrichment in pathways related to ion transportation and osmolyte production to cope with induced osmotic pressure due to high salt concentration. Pathways related to signal transduction (MAPK, FOXO and phosphatidylinositol signaling), and environmental information processing were also upregulated under hypersalinity. Energy metabolism and innate immune response pathways also appear to be regulated. Protein turnover was high at 8ppt as evidenced by enrichment of the proteasome and aminoacyl tRNA synthesis pathways, along with other enriched KEGG terms such as apoptosis, cellular senescence and cell cycle.

CONCLUSION

Altogether, the RNA-seq analysis provided valuable insights into competitive endogenous (lncRNA-miRNA-mRNA) regulatory network of L. rohita under salinity stress. L. rohita is adapting to the salinity stress by means of upregulating protein turnover, osmolyte production and removing the damaged cells using apoptotic pathway and regulating the cell growth and hence diverting the essential energy for coping with salinity stress.

Highly Diluted Glyphosate Mitigates Its Effects on Artemia salina: Physicochemical Implications

Glyphosate is an herbicide widely used in agriculture but can present chronic toxicity in low concentrations. Artemia salina is a common bio-indicator of ecotoxicity; it was used herein as a model to evaluate the effect of highly diluted-succussed glyphosate (potentized glyphosate) in glyphosate-based herbicide (GBH) exposed living systems. Artemia salina cysts were kept in artificial seawater with 0.02% glyphosate (corresponding to 10% lethal concentration or LC10) under constant oxygenation, luminosity, and controlled temperature, to promote hatching in 48 h. Cysts were treated with 1% (v/v) potentized glyphosate in different dilution levels (Gly 6 cH, 30 cH, 200 cH) prepared the day before according to homeopathic techniques, using GBH from the same batch. Controls were unchallenged cysts, and cysts treated with succussed water or potentized vehicle. After 48 h, the number of born nauplii per 100 µL, nauplii vitality, and morphology were evaluated. The remaining seawater was used for physicochemical analyses using solvatochromic dyes. In a second set of experiments, Gly 6 cH treated cysts were observed under different degrees of salinity (50 to 100% seawater) and GBH concentrations (zero to LC 50); hatching and nauplii activity were recorded and analyzed using the ImageJ 1.52, plug-in Trackmate. The treatments were performed blind, and the codes were revealed after statistical analysis. Gly 6 cH increased nauplii vitality (p = 0.01) and improved the healthy/defective nauplii ratio (p = 0.005) but delayed hatching (p = 0.02). Overall, these results suggest Gly 6cH treatment promotes the emergence of the more GBH-resistant phenotype in the nauplii population. Also, Gly 6cH delays hatching, another useful survival mechanism in the presence of stress. Hatching arrest was most marked in 80% seawater when exposed to glyphosate at LC10. Water samples treated with Gly 6 cH showed specific interactions with solvatochromic dyes, mainly Coumarin 7, such that it appears to be a potential physicochemical marker for Gly 6 cH. In short, Gly 6 cH treatment appears to protect the Artemia salina population exposed to GBH at low concentrations.

Transcriptome analysis revealed the mechanism of Luciobarbus capito (L. capito) adapting high salinity: Antioxidant capacity, heat shock proteins, immunity

Salinity has a significant influence on the physiology of freshwater aquatic organisms. However, there are few studies on the hematology and immunology of freshwater fish under high salinity. In the current study, we aimed to analyze the adaptive effect of salt stress on L. capito spleen immune function and hematology using transcriptomic analysis. We replicated a L. capito acute salinity stress model, and collected blood and spleens from freshwater and saltwater fish. It was found that salinity affected significantly the numbers of leukocytes, lymphocytes, neutrophils, and red blood cells, as well as the content of haemoglobin. Salt treatment resulted in a significant increase in the expression of HSP70, HSP90, CAT, SOD, and GPX1 genes in L. capito spleens. Transcriptomic analysis revealed a total of 546 differentially expressed genes (DEGs) in spleens, including 224 up-regulated DEGs and 322 down-regulated DEGs. In addition, GO enrichment analysis revealed immune system process, multicellular organismal process, and biological regulation of genes with the most differences in biological processes. KEGG enrichment analysis showed that the regulation of lipolysis in adipocyte, FoxO signaling pathway, Hematopoietic cell lineage signaling pathway, and HIF-1 signaling pathway were significantly enriched. L. capito adapted oxidative to high salinity through FoxO signaling pathway and immune to high salinity through Hematopoietic cell lineage signaling pathway. At the same time, we selected 10 DEGs for qRT-PCR detection, and the results showed that the qRT-PCR results were consistent with our RNA-Seq results, indicating that transcriptome sequencing was accurate and reliable. In conclusion, our results demonstrated that the improvement of antioxidant capacity, heat shock protein and immunity are involved in the molecular mechanism of L. capito adapting to high salinity. Our findings provided a rationale for further study on high salinity adaptation and related enrichment pathways.

Effect of heat and hypoxia stress on mitochondrion and energy metabolism in the gill of hard clam

Aquatic animals suffer from heat and hypoxia stress more frequently due to global climate change and other anthropogenic activities. Heat and hypoxia stress can significantly affect mitochondrial function and energy metabolism. Here, the response and adaptation characteristics of mitochondria and energy metabolism in the gill of the hard clam Mercenaria mercenaria under heat (35 °C), hypoxia (0.2 mg/L), and heat plus hypoxia stress (35 °C, 0.2 mg/L) after 48 h exposure were investigated. Mitochondrial membrane potentials were depolarized under environmental stress. Mitochondrial fusion, fission and mitophagy played a key role in maintain mitochondrion function. The AMPK subunits showed different expression under environmental stress. Acceleration of enzyme activities (phosphofructokinase, pyruvate kinase and lactic dehydrogenase) and accumulation of anaerobic metabolites in glycolysis and TCA cycle implied that the anaerobic metabolism might play a key role in providing energy. Accumulation of amino acids might help to increase tolerance under heat and heat combined hypoxia stress. In addition, urea cycle played a key role in amino acid metabolism to prevent ammonia/nitrogen toxicity. This study improved our understanding of the mitochondrial and energy metabolism responses of marine bivalves exposed to environmental stress.

Metabolism response mechanism in the gill of Oreochromis mossambicus under salinity, alkalinity and saline-alkalinity stresses

Saline-alkalinity is one of the important ecological parameter that has an impact function on the physiological metabolism, osmoregulation, survival, growth, development and distribution of teleost fish. Oreochromis mossambicus, a species of euryhaline that can withstand a wide variety of salinities, may be used as a research model animal in environmental studies. In order to detect the metabolism responses and mechanisms of different osmotic stresses tolerance in the gills of O. mossambicus, in present study, the metabolic responses of O. mossambicus subjected to salinity (25 g/L, S_S), alkalinity (4 g/L, A_S) and saline-alkalinity stress (salinity: 25 g/L, alkalinity: 4 g/L; SA_S) with the control environment (freshwater, C_S) were investigated by LC-MS/MS-based metabolomics. The metabolism results indicated that numerous metabolites were identified between the stress groups and the control group. In addition, under three osmotic stresses, the amino acid and carbohydrate metabolism, levels of amino acids, osmolytes and energy substances, such as L-lysine, arachidonic acid, docosahexaenoic acids, creatine and taurine, were significantly affected and changed in the metabolism of the gills of O. mossambicus. The metabolism data indicated that signal transduction and regulation pathways, including FoxO signaling pathway, mTOR signaling pathway and prolactin signaling pathway, were enriched in the gill during adaptation to high salinity, alkalinity and saline-alkalinity stress. The results of this study provide more comprehensive and reliable data for the osmotic pressure regulation mechanism and biological response of euryhaline teleost, and provide reliable scientific basis for the breeding and research of high salinity tolerance population, and further promote the development and utilization of saline-alkalinity water resources.

Transcriptome Analysis of Marbled Rockfish Sebastiscus marmoratus under Salinity Stress

The marbled rockfish, Sebastiscus marmoratus, belongs to the euryhaline fish and is an oviparous scleractinian fish. There are few studies on the adaptation mechanism, functional genes, and related pathways of S. marmoratus and salinity. The results showed that a total of 72.1 GB of clean reads were obtained and all clean reads annotated a total of 25,278 Unigenes, of which 2,160 were novel genes. Compared to 20‱, 479 and 520 differential genes were obtained for 35‱ and 10‱, respectively. Gene ontology (GO) enrichment analysis revealed significant enrichment in protein binding, ion binding, ATP binding, and catalytic activity. Kyoto Encyclopedia of Genes and Genomes (KEGG) showed that differentially expressed genes significantly expressed under salinity stress were mainly involved in the pathways of the cytochrome P450 metabolism of xenobiotics, tryptophan metabolism, cellular senescence, and calcium signaling pathways. Among them, pik3r6b, cPLA2γ-like, and WSB1 were differentially expressed in all three groups, and they were associated with apoptosis, inflammation, DNA damage, immune regulation, and other physiological processes. Six differentially expressed genes were randomly selected for qRT-PCR validation, and the results showed that the transcriptomic data were of high confidence.

Cellular stress response and acclimation capacity of the ditch shrimp Palaemon varians to extreme weather events - How plastic can a plastic species be?

Species from shallow marine environments are particularly vulnerable to extreme weather events (heatwaves and extreme rainfall) that can promote abrupt environmental shifts, namely in temperature and salinity (respectively). To assess how these shifts impact species' cellular stress responses (CSR), ditch shrimps Palaemon varians were exposed to a chronic (28 days) thermohaline stress experiment. Three levels of temperature (20, 23 and 26 °C) and two levels of salinity (20 and 40) were tested in a full factorial experiment, and shrimps sampled at the 7th, 14th, 21st and 28th day of exposure. Survival, wet weight (as proxy for growth), and cellular stress biomarkers associated with oxidative stress (LPO - Lipid Peroxidation, GST - Glutathione-S-Transferase, SOD - Superoxide Dismutase, TAC - Total Antioxidant Capacity and CAT - Catalase) and protein denaturation (UBI - Ubiquitin and HSP-70 - Heat Shock Protein 70 kDa) were analysed in shrimps' muscle at each sampling day. Temperature and time of exposure significantly affected biomarker levels, with shrimps exposed to 20 and 26 °C revealing more pronounced differences. No interactions were detected between temperature and salinity, suggesting that these factors display additive effects on shrimps' CSR. Antioxidant agents (CAT and TAC) increased under elevated temperature, while protein denaturation markers (UBI and HSP-70) were mostly affected by time of exposure, decreasing at 28 days. Total protein reserves increased throughout time and no effects on wet weight were observed. A negative correlation between wet weight and HSP-70 was detected, suggesting that HSP-70 levels are dependent on organism size. Peak survival (~73 %) was found under 20 °C and salinity 40 and lower survival (~30-40 %) was associated with higher temperatures (23 and 26 °C) and lower salinity (20). We conclude that P. varians displays some level of acclimation capacity but differences in survival may indicate effects on osmoregulation processes and the need for longer timeframes to fully acclimate to heat and hyposaline stress.

In Vitro Membrane Platform for the Visualization of Water Impermeability across the Liquid-Ordered Phase under Hypertonic Conditions

Passive water penetration across the cell membrane by osmotic diffusion is essential for the homeostasis of cell volume, in addition to the protein-assisted active transportation of water. Since membrane components can regulate water permeability, controlling compositional variation during the volume regulatory process is a prerequisite for investigating the underlying mechanisms of water permeation and related membrane dynamics. However, the lack of a viable in vitro membrane platform in hypertonic solutions impedes advanced knowledge of cell volume regulation processes, especially cholesterol-enriched lipid domains called lipid rafts. By reconstituting the liquid-ordered (L_o) domain as a likeness of lipid rafts, we verified suppressed water permeation across the L_o domains, which had yet to be confirmed with experimental demonstrations despite a simulation approach. With the help of direct transfer of the L_o domains from vesicles to supported lipid membranes, the biological roles of lipid composition in suppressed water translocation were experimentally confirmed. Additionally, the improvement in membrane stability under hypertonic conditions was demonstrated based on molecular dynamics simulations.

Gilthead Seabream Liver Integrative Proteomics and Metabolomics Analysis Reveals Regulation by Different Prosurvival Pathways in the Metabolic Adaptation to Stress

The study of the molecular mechanisms of stress appraisal on farmed fish is paramount to ensuring a sustainable aquaculture. Stress exposure can either culminate in the organism's adaptation or aggravate into a metabolic shutdown, characterized by irreversible cellular damage and deleterious effects on fish performance, welfare, and survival. Multiomics can improve our understanding of the complex stressed phenotype in fish and the molecular mediators that regulate the underlying processes of the molecular stress response. We profiled the stress proteome and metabolome of Sparus aurata responding to different challenges common to aquaculture production, characterizing the disturbed pathways in the fish liver, i.e., the central organ in mounting the stress response. Label-free shotgun proteomics and untargeted metabolomics analyses identified 1738 proteins and 120 metabolites, separately. Mass spectrometry data have been made fully accessible via ProteomeXchange, with the identifier PXD036392, and via MetaboLights, with the identifier MTBLS5940. Integrative multivariate statistical analysis, performed with data integration analysis for biomarker discovery using latent components (DIABLO), depicted the 10 most-relevant features. Functional analysis of these selected features revealed an intricate network of regulatory components, modulating different signaling pathways related to cellular stress, e.g., the mTORC1 pathway, the unfolded protein response, endocytosis, and autophagy to different extents according to the stress nature. These results shed light on the dynamics and extent of this species' metabolic reprogramming under chronic stress, supporting future studies on stress markers' discovery and fish welfare research.

Blood biomarkers as diagnostic tools: An overview of climate-driven stress responses in fish

Global climate change due to anthropogenic activities affects the dynamics of aquatic communities by altering the adaptive capacities of their inhabitants. Analysis of blood provides valuable insights in the form of a comprehensive representation of the physiological and functional status of fish under various environmental and treatment conditions. This review synthesizes currently available information about blood biomarkers used in climate change induced stress responses in fish. Alterations in informative blood-based indicators are used to monitor the physiological fitness of individual fishes or entire populations. Specific characteristics of fish blood, such as serum and plasma metabolites, cell composition, cellular abnormalities, cellular and antioxidant enzymes necessitate adapted protocols, as well as careful attention to experimental designs and meticulous interpretation of patterns of data. Moreover, the sampling technique, transportation, type of culture system, acclimation procedure, and water quality must all be considered for valid interpretation of hemato-biochemical parameters. Besides, blood collection, handling, and storage time of blood samples can all have significant impacts on the results of a hematological analysis, so it is optimal to perform hemato-biochemical evaluations immediately after blood collection because long-term storage can alter the results of the analyses, at least in part as a result of storage-related degenerative changes that may occur. However, the scarcity of high-throughput sophisticated approaches makes fish blood examination studies promising for climate-driven stress responses in fish.

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.

Steroidogenic Effects of Salinity Change on the Hypothalamus-Pituitary-Gonad (HPG) Axis of Male Chinese Sea Bass (Lateolabrax maculatus)

As lower vertebrates, teleost species could be affected by dynamic aquatic environments and may respond to environmental changes through the hypothalamus–pituitary–gonad (HPG) axis to ensure their normal growth and sexual development. Chinese sea bass (Lateolabrax maculatus), euryhaline marine teleosts, have an extraordinary ability to deal with a wide range of salinity changes, whereas the salinity decrease during their sex-maturation season may interfere with the HPG axis and affect their steroid hormone metabolism, resulting in abnormal reproductive functioning. To this end, in this study, 40 HPG axis genes in the L. maculatus genome were systematically characterized and their copy numbers, phylogenies, gene structures, and expression patterns were investigated, revealing the conservation of the HPG axis among teleost lineages. In addition, freshwater acclimation was carried out with maturing male L. maculatus, and their serum cortisol and 11-ketotestosterone (11-KT) levels were both increased significantly after the salinity change, while their testes were found to be partially degraded. After salinity reduction, the expression of genes involved in cortisol and 11-KT synthesis (cyp17a, hsd3b1, cyp21a, cyp11c, hsd11b2, and hsd17b3) showed generally upregulated expression in the head kidneys and testes, respectively. Moreover, cyp11c and hsd11b2 were involved in the synthesis and metabolism of both cortisol and 11-KT, and after salinity change their putative interaction may contribute to steroid hormone homeostasis. Our results proved the effects of salinity change on the HPG axis and steroidogenic pathway in L. maculatus and revealed the gene interactions involved in the regulation of steroid hormone levels. The coordinated interaction of steroidogenic genes provides comprehensive insights into steroidogenic pathway regulation, as well as sexual development, in teleost species.

Endocrine and osmoregulatory responses to tidally-changing salinities in fishes

Salinity is one of the main physical properties that govern the distribution of fishes across aquatic habitats. In order to maintain their body fluids near osmotic set points in the face of salinity changes, euryhaline fishes rely upon tissue-level osmotically-induced responses and systemic endocrine signaling to direct adaptive ion-transport processes in the gill and other critical osmoregulatory organs. Some euryhaline teleosts inhabit tidally influenced waters such as estuaries where salinity can vary between fresh water (FW) and seawater (SW). The physiological adaptations that underlie euryhalinity in teleosts have been traditionally identified in fish held under steady-state conditions or following unidirectional transfers between FW and SW. Far fewer studies have employed salinity regimes that simulate the tidal cycles that some euryhaline fishes may experience in their native habitats. With an emphasis on prolactin (Prl) signaling and branchial ionocytes, this mini-review contrasts the physiological responses between euryhaline fish responding to tidal versus unidirectional changes in salinity. Three patterns that emerged from studying Mozambique tilapia (Oreochromis mossambicus) subjected to tidally-changing salinities include, 1) fish can compensate for continuous and marked changes in external salinity to maintain osmoregulatory parameters within narrow ranges, 2) tilapia maintain branchial ionocyte populations in a fashion similar to SW-acclimated fish, and 3) there is a shift from systemic to local modulation of Prl signaling.