Heat shock proteins (chaperones) in fish and shellfish and their potential role in relation to fish health: a review

New insights into the regulation mechanism of red claw crayfish (Cherax quadricarinatus) hepatopancreas under air exposure using transcriptome analysis

Red claw crayfish (Cherax quadricarinatus) is an important freshwater shrimp species worldwide with enormous economic value. Waterless transportation is an inherent feature of red claw crayfish transportation. However, the high mortality of red claw crayfish is a severe problem in the aquaculture of crayfish after waterless transportation. In this study, we investigated the responses of the hepatopancreas from the red claw crayfish undergoing air exposure stress and normal conditions on transcriptome levels. We used Illumina-based RNA sequencing (RNA-Seq) to perform a transcriptome analysis from the hepatopancreas of red claw crayfish challenged by air exposure. An average of 57,148,800 clean reads per library was obtained, and 33,567 unigenes could be predicted and classified according to their homology with matches in the National Center for Biotechnology Information (NCBI) non-redundant protein sequences (Nr), Gene Ontology (GO), a manually annotated and reviewed protein sequence database (Swiss-Prot), protein families (Pfam), Clusters of Orthologous Groups (COG) of proteins, and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. 690 and 3407 differentially expressed genes (DEGs) were identified between the two stress stages of the red claw crayfish. More DEGs were identified in 12 h, indicating that gene expressions were largely changed at 12 h. Some immune-related pathways and genes were identified according to KEGG and GO enrichment analysis. A total of 12 DEGs involved in immune response and trehalose mechanism were verified by quantitative real-time-polymerase chain reaction (qRT-PCR). The results indicated that the red claw crayfish might counteract the stress of air exposure at the transcriptomic level by increasing expression levels of antioxidant-, immune-, and trehalose metabolism-related genes. These transcriptome results from the hepatopancreas provide significant insights into the influence mechanism of air exposure to the trehalose mechanism and immune response in the red claw crayfish.

Gill Oxidative Stress Protection through the Use of Phytogenics and Galactomannan Oligosaccharides as Functional Additives in Practical Diets for European Sea Bass (Dicentrarchus labrax) Juveniles

The aim of the present study is to evaluate the potential of two functional additives as gill endogenous antioxidant capacity boosters in European sea-bass juveniles fed low-FM/FO diets when challenged against physical and biological stressors. For that purpose, two isoenergetic and isonitrogenous diets with low FM (10%) and FO (6%) contents were supplemented with 5000 ppm plant-derived galactomannan-oligosaccharides (GMOS) or 200 ppm of a mixture of garlic and labiate plant essential oils (PHYTO). A control diet was void from supplementation. Fish were fed the experimental diet for nine weeks and subjected to a confinement stress challenge (C challenge) or a confinement stress challenge combined with an exposure to the pathogen Vibrio anguillarum (CI challenge). Both GMOS and PHYTO diets attenuated fish stress response, inducing lower circulating plasma cortisol and down-regulating nfκβ2 and gr relative gene-expression levels in the gill. This attenuated stress response was associated with a minor energetic metabolism response in relation to the down-regulation of nd5 and coxi gene expression.

Heat Shock Proteins (Hsps) in Cellular Homeostasis: A Promising Tool for Health Management in Crustacean Aquaculture

Heat shock proteins (Hsps) are a family of ubiquitously expressed stress proteins and extrinsic chaperones that are required for viability and cell growth in all living organisms. These proteins are highly conserved and produced in all cellular organisms when exposed to stress. Hsps play a significant role in protein synthesis and homeostasis, as well as in the maintenance of overall health in crustaceans against various internal and external environmental stresses. Recent reports have suggested that enhancing in vivo Hsp levels via non-lethal heat shock, exogenous Hsps, or plant-based compounds, could be a promising strategy used to develop protective immunity in crustaceans against both abiotic and biotic stresses. Hence, Hsps as the agent of being an immune booster and increasing disease resistance will present a significant advancement in reducing stressful conditions in the aquaculture system.

Toxicity of synthesized silver nanoparticles in a widespread fish: A comparison between green and chemical

Metallic nanoparticles are gaining importance in various fields of life due to their large surface area to volume ratio. However, metallic nanoparticles pose different toxic effects on fish when they appear with different shapes and compositions in water. Herein the present study was designed to evaluate the median (LC₅₀) and sub-lethal (1/10th of LC₅₀) concentrations of Ag-Green NPs, 700 μg/L for Ag-Chem NPs, and 50 μg/L for Ag₂O-Chem NPs were confirmed in Hypophthalmichthys molitrix. Furthermore, exposure of H. molitrix fingerlings to 10 % of LC₅₀ concentration of these particles induced significantly higher (p < 0.05) activities of serum alanine transaminase, aspartate aminotransferase, lactate dehydrogenase, white blood cells, acetylcholinesterase and catalase, superoxide dismutase, peroxidase, relative gene expressions of antioxidant enzymes, heat shock protein (Hsp70), hypoxia- inducible factor 1-alpha (HIF-1α) and lipid peroxidase level than the control, but decreased hematological parameters with less effects of Ag-Green NPs than chemically synthesized AgNPs. Moreover, the histopathological study also indicated morphological changes in the liver and gills of treated fish groups. The comparative toxicity evaluation revealed the maximum negative effect of Ag₂O-Chem NPs followed by Ag-Chem NPs while Ag-Green NPs showed the least toxic effects. Based on our results, replacement of chemically synthesized NPs to green synthesized AgNPs can be recommended in large scale application to reduce the noxious effects to aquatic environment.

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.

A different transcriptional landscape sheds light on Russian sturgeon (Acipenser gueldenstaedtii) mechanisms to cope with bacterial infection and chronic heat stress

Sturgeons are chondrostean fish of high economic value and critically endangered due to anthropogenic activities, which has led to sturgeon aquaculture development. Russian sturgeon (Acipenser gueldenstaedtii), the second most important species reared for caviar, is successfully farmed in subtropical countries, including Uruguay. However, during the Uruguayan summer, sturgeons face intolerable warmer temperatures that weaken their defences and favour infections by opportunistic pathogens, increasing fish mortality and farm economic losses. Since innate immunity is paramount in fish, for which the liver plays a key role, we used deep RNA sequencing to analyse differentially expressed genes in the liver of Russian sturgeons exposed to chronic heat stress and challenged with Aeromonas hydrophila. We assembled 149.615 unigenes in the Russian sturgeon liver transcriptome and found that metabolism and immune defence pathways are among the top five biological processes taking place in the liver. Chronic heat stress provoked profound effects on liver biological functions, up-regulating genes related to protein folding, heat shock response and lipid and protein metabolism to meet energy demands for coping with heat stress. Besides, long-term exposure to heat stress led to cell damage triggering liver inflammation and diminishing liver ability to mount an innate response to A. hydrophila challenge. Accordingly, the reprogramming of liver metabolism over an extended period had detrimental effects on fish health, resulting in weight loss and mortality, with the latter increasing after A. hydrophila challenge. To our knowledge, this is the first transcriptomic study describing how chronic heat-stressed sturgeons respond to a bacterial challenge, suggesting that liver metabolism alterations have a negative impact on the innate anti-bacterial response.

Metabolic scope, performance and tolerance of juvenile European sea bass Dicentrarchus labrax upon acclimation to high temperatures

European sea bass is a species of great commercial value for fisheries and aquaculture. Rising temperatures may jeopardize the performance and survival of the species across its distribution and farming range, making the investigation of its thermal responses highly relevant. In this article, the metabolic scope, performance, and tolerance of juvenile E. sea bass reared under three high water temperatures (24, 28, 33°C), for a period of three months was evaluated via analysis of selected growth performance and physiological indicators. Effects on molecular, hormonal, and biochemical variables were analyzed along with effects of acclimation temperature on the metabolic rate and Critical Thermal maximum (CT_max). Despite signs of thermal stress at 28°C indicated by high plasma cortisol and lactate levels as well as the upregulation of genes coding for Heat Shock Proteins (HSP), E. sea bass can maintain high performance at that temperature which is encouraging for the species culture in the context of a warming ocean. Critical survivability thresholds appear sharply close to 33°C, where the aerobic capacity declines and the overall performance diminishes. European sea bass demonstrates appreciable capacity to cope with acute thermal stress exhibiting CT_max as high as 40°C for fish acclimated at high temperatures, which may indicate resilience to future heatwaves events.

Schizothorax prenanti Heat Shock Protein 27 Gene: Cloning, Expression, and Comparison with Other Heat Shock Protein Genes after Poly (I:C) Induction

We identified and cloned cDNA encoding the heat shock protein (Hsp) 27 gene from Schizothorax prenanti (SpHsp27), and compared its expression with that of SpHsp60, SpHsp70, and SpHsp90 in the liver, head kidney, hindgut, and spleen of S. prenanti that were injected with polyinosinic-polycytidylic acid [Poly (I:C)]. The SpHsp27 partial cDNA (sequence length, 653 bp; estimated molecular mass, 5.31 kDa; theoretical isoelectric point, 5.09) contained an open reading frame of 636 bp and a gene encoding 211 amino acids. The SpHsp27 amino acid sequence shared 61.0−92.89% identity with Hsp27 sequences from other vertebrates and SpHsp27 was expressed in seven S. prenanti tissues. Poly (I:C) significantly upregulated most SpHsps genes in the tissues at 12 or 24 h (p < 0.05) compared with control fish that were injected with phosphate-buffered saline. However, the intensity of responses of the four SpHsps was organ-specifically increased. The expression of SpHsp27 was increased 163-fold in the head kidney and 26.6-fold SpHsp27 in the liver at 24 h after Poly (I:C) injection. In contrast, SpHsp60 was increased 0.97−1.46-fold in four tissues and SpHsp90 was increased 1.21- and 1.16-fold in the liver and spleen at 12 h after Poly (I:C) injection. Our findings indicated that Poly (I:C) induced SpHsp27, SpHsp60, SpHsp70, and SpHsp90 expression and these organ-specific SpHsps are potentially involved in S. prenanti antiviral immunity or mediate pathological process.

Seasonal differences in thermal stress susceptibility of diploid and triploid brook trout, Salvelinus fontinalis (Teleostei, Pisces)

Many physiological processes of teleost fish show periodicity due to intrinsic rhythms. It may be hypothesized that also susceptibility to thermal stress differs seasonally. To shed more light on this problem the following experiment was conducted. Diploid and triploid Salvelinus fontinalis were kept at an acclimation temperature of 9°C and at a natural photoperiod typical for the Northern Hemisphere during their entire live. During eight different periods of the year, different subgroups were exposed to a 32 day lasting thermal stress of 20°C. Rate of fish maintaining equilibrium, daily growth rate, condition factor, viscerosomatic index and hepato-somatic index were measured. Complementary mRNA expression of genes characterizing growth (GHR1, GHR2), proteolysis (Protreg, Protα5), stress (Hsp47, Hsp90) and respiratory energy metabolism (ATPJ52) was determined. Seasonal differences in thermal stress susceptibility of 2n and 3n S. fontinalis were detected. It was highest from September to December and moderate from January to March. During the remaining period of the year, susceptibility to thermal stress was minimal. Increased thermal stress susceptibility was related to decreased rates of fish maintaining equilibrium, decreased growth rates, reduction of viscera and liver mass and changes in mRNA expression of genes characterizing proteolysis, growth, respiratory energy metabolism and stress. The differences in seasonal stress susceptibility were minor between 2n and 3n S. fontinalis. The data are valuable for ecology and fish culture to identify periods when animals are most susceptible to thermal stress.

RNA-Seq and 16S rRNA Analysis Revealed the Effect of Deltamethrin on Channel Catfish in the Early Stage of Acute Exposure

Deltamethrin (Del) is a widely used pyrethroid insecticide and a dangerous material that has brought serious problems to the healthy breeding of aquatic animals. However, the toxicological mechanisms of Del on channel catfish remain unclear. In the present study, we exposed channel catfish to 0, 0.5, and 5 μg/L Del for 6 h, and analyzed the changes in histopathology, trunk kidney transcriptome, and intestinal microbiota composition. The pathological analyses showed that a high concentration of Del damaged the intestine and trunk kidney of channel catfish in the early stage. The transcriptome analysis detected 32 and 1837 differentially expressed genes (DEGs) in channel catfish trunk kidneys after exposure to 0.5 and 5 μg/L Del, respectively. Moreover, the KEGG pathway and GO enrichment analyses showed that the apoptosis signaling pathway was significantly enriched, and apoptosis-related DEGs, including cathepsin L, p53, Bax, and caspase-3, were also detected. These results suggested that apoptosis occurs in the trunk kidney of channel catfish in the early stage of acute exposure to Del. We also detected some DEGs and signaling pathways related to immunity and drug metabolism, indicating that early exposure to Del can lead to immunotoxicity and metabolic disorder of channel catfish, which increases the risk of pathogenic infections and energy metabolism disorders. Additionally, 16S rRNA gene sequencing showed that the composition of the intestinal microbiome significantly changed in channel catfish treated with Del. At the phylum level, the abundance of Firmicutes, Fusobacteria, and Actinobacteria significantly decreased in the early stage of Del exposure. At the genus level, the abundance of Romboutsia, Lactobacillus, and Cetobacterium decreased after Del exposure. Overall, early exposure to Del can lead to tissue damage, metabolic disorder, immunotoxicity, and apoptosis in channel catfish, and affect the composition of its intestinal microbiota. Herein, we clarified the toxic effects of Del on channel catfish in the early stage of exposure and explored why fish under Del stress are more vulnerable to microbial infections and slow growth.

Multiple isoforms of HSP70 and HSP90 required for betanodavirus multiplication in medaka cells

Heat shock proteins (HSPs) are molecular chaperones that have recently been shown to function as host factors (HFs) for virus multiplication in fish as well as in mammals, plants, and insects. HSPs are classified into families, and each family has multiple isoforms. However, no comprehensive studies have been performed to clarify the biological importance of these multiple isoforms for fish virus multiplication. Betanodaviruses are the causative agents of viral nervous necrosis in cultured marine fish and cause very high mortality. Although the viral genome and encoded proteins have been characterized extensively, information on HFs for these viruses is limited. In this study, therefore, we focused on the HSP70 and HSP90 families to examine the importance of their isoforms for betanodavirus multiplication. We found that HSP inhibitors (17-AAG, radicicol, and quercetin) suppressed viral RNA replication and production of progeny virus in infected medaka (Oryzias latipes) cells. Thermal stress or virus infection resulted in increased expression of some isoform genes and facilitated virus multiplication. Furthermore, overexpression and knockdown of some isoform genes revealed that the isoforms HSP70-1, HSP70-2, HSP70-5, HSP90-α1, HSP90-α2, and HSP90-β play positive roles in virus multiplication in medaka. Collectively, these results suggest that multiple isoforms of fish HPSs serve as HFs for betanodavirus multiplication.

Transcriptomic response in thermally challenged seahorses Hippocampus erectus: The effect of magnitude and rate of temperature change

Hippocampus erectus inhabiting the shallow coastal waters of the southern Gulf of Mexico are naturally exposed to marked temperature variations occurring in different temporal scales. Under such heterogeneous conditions, a series of physiological and biochemical adjustments take place to restore and maintain homeostasis. This study investigated the molecular mechanisms involved in the response of H. erectus to increased temperature using transcriptome analysis based on RNA-Seq technology. Data was obtained from seahorses after 0.5-h exposure to combinations of different target temperatures (26 °C: control, and increased to 30 and 33 °C) and rates of thermal increase (abrupt: < 5 min; gradual: 1-1.5 °C every 3 h). The transcriptome of seahorses was assembled de novo using Trinity software to obtain 29,211 genes and 30,479 transcripts comprising 27,520,965 assembled bases. Seahorse exposure to both 30 and 33 °C triggered characteristic processes of the cellular stress response, regardless of the rate of thermal change. The transcriptomic profiles of H. erectus suggest an arrest of muscle development processes, the activation of heat shock proteins, and a switch to anaerobic metabolism within the first 0.5 h of exposure to target temperatures to ensure energy supply. Interestingly, apoptotic processes involving caspase were activated principally in gradual treatments, suggesting that prolonged exposure to even sublethal temperatures results in the accumulation of deleterious effects that may eventually terminate in cellular death. Results herein validate 30 °C and 33 °C as potential upper limits of thermal tolerance for H. erectus at the southernmost boundary of its geographic distribution.

Modulation of humoral immunological and antioxidant responses and gut bacterial community and gene expression in rainbow trout, Oncorhynchus mykiss, by dietary lactic acid supplementation

The present study was conducted to find the effects of dietary lactic acid (LA) supplementation on growth performance, hematological characteristics, humoral antioxidant and immunological factors, intestinal gene expression and bacteriological parameters in rainbow trout, Oncorhynchus mykiss. The fish (104 ± 0.90 g) were randomly distributed in twelve tanks (150 L water) as four treatments, receiving diets supplemented with 0, 5, 10, and 20 g/kg LA for 70 days. At the end of the feeding trial, no significant differences were observed in the fish growth performance and survival among the treatments. Blood/plasma red blood cell (5-20 g/kg LA), white blood cell (10 g/kg LA), hematocrit (5 and 10 g/kg LA), hemoglobin (5 and 10 g/kg LA), superoxide dismutase (10 g/kg LA), glutathione peroxidase (10 g/kg LA), total antioxidant capacity (10 g/kg LA), lysozyme (5-20 g/kg LA), and alternative complement activity (10 g/kg LA) significantly increased, as malondialdehyde (10 g/kg LA) significantly decreased in the LA-treated fish. Dietary LA supplementation induced no significant changes in the intestinal defensin gene expression, but significantly up-regulated the expression of toll-like receptor-3 (5-20 g/kg LA), Mx-9 (5-20 g/kg LA), and heat shock protein-70 (5 g/kg LA) genes; the highest expressions were observed at 5 g/kg LA supplementation. Dietary LA supplementation significantly increased total bacterial count (5 and 10 g/kg LA), Lactobacillus sp. (5-20 g/kg LA), and Bacteroides sp. (5-20 g/kg LA), but decreased Streptococcus iniae (5-20 g/kg LA) in the fish intestine; the highest Lactobacillus sp. And Bacteroides sp. Were observed in 10 and 5 g/kg LA supplementation, respectively. Overall, dietary LA supplementation, although has no significant effects on the fish growth performance, is beneficial to improve humoral antioxidant parameters, humoral and intestinal immunological parameters and intestinal microflora. According to the results, dietary 5-10 g/kg LA is recommended for the formulation of rainbow trout feed.

Feed Restriction Alleviates Chronic Thermal Stress-Induced Liver Oxidation and Damages via Reducing Lipid Accumulation in Channel Catfish (Ictalurus punctatus)

Caloric restriction is known to suppress oxidative stress in organ systems. However, whether caloric/feed restriction alleviates chronic thermal stress in aquatic animals remains unknown. Here, we set up three feeding rations: 3% BW (3% body weight/day), 2.5% BW (restricted feeding, 2.5% body weight/day) and 2% BW (high restricted feeding, 2% body weight/day), to investigate the effects and mechanism of feed restriction on improving chronic heat-induced (27 to 31 °C) liver peroxidation and damages in channel catfish (Ictalurus punctatus). The results showed that, compared to 3% BW, both 2.5% BW and 2% BW significantly reduced the liver expressions of hsc70, hsp70 and hsp90, but only 2.5% BW did not reduce the growth performance of channel catfish. The 2.5% BW and 2% BW also reduced the lipid deposition (TG) and improved the antioxidant capacity (CAT, SOD, GSH and T-AOC) in the liver of channel catfish. The heat-induced stress response (plasma glucose, cortisol and NO) and peroxidation (ROS and MDA) were also suppressed by either 2.5% BW or 2% BW. Moreover, 2.5% BW or 2% BW overtly alleviated liver inflammation and damages by reducing endoplasmic reticulum (ER) stress (BIP and Calnexin) and cell apoptosis (BAX, Caspase 3 and Caspase 9) in the liver of channel catfish. In conclusion, 2.5% body weight/day is recommended to improve the antioxidant capacity and liver health of channel catfish during the summer season, as it alleviates liver peroxidation and damages via suppressing lipid accumulation under chronic thermal stress.

CO2 induced seawater acidification impacts survival and development of European eel embryos

Fish embryos may be vulnerable to seawater acidification resulting from anthropogenic carbon dioxide (CO₂) emissions or from excessive biological CO₂ production in aquaculture systems. This study investigated CO₂ effects on embryos of the European eel (Anguilla anguilla), a catadromous fish that is considered at risk from climate change and that is targeted for hatchery production to sustain aquaculture of the species. Eel embryos were reared in three independent recirculation systems with different pH/CO₂ levels representing “control” (pH 8.1, 300 μatm CO₂), end-of-century climate change (“intermediate”, pH 7.6, 900 μatm CO₂) and “extreme” aquaculture conditions (pH 7.1, 3000 μatm CO₂). Sensitivity analyses were conducted at 4, 24, and 48 hours post-fertilization (hpf) by focusing on development, survival, and expression of genes related to acute stress response (crhr1, crfr2), stress/repair response (hsp70, hsp90), water and solute transport (aqp1, aqp3), acid-base regulation (nkcc1a, ncc, car15), and inhibitory neurotransmission (GABAAα6b, Gabra1). Results revealed that embryos developing at intermediate pH showed similar survival rates to the control, but egg swelling was impaired, resulting in a reduction in egg size with decreasing pH. Embryos exposed to extreme pH had 0.6-fold decrease in survival at 24 hpf and a 0.3-fold change at 48 compared to the control. These observed effects of acidification were not reflected by changes in expression of any of the here studied genes. On the contrary, differential expression was observed along embryonic development independent of treatment, indicating that the underlying regulating systems are under development and that embryos are limited in their ability to regulate molecular responses to acidification. In conclusion, exposure to predicted end-of-century ocean pCO₂ conditions may affect normal development of this species in nature during sensitive early life history stages with limited physiological response capacities, while extreme acidification will negatively influence embryonic survival and development under hatchery conditions.

Gill and Liver Transcript Expression Changes Associated With Gill Damage in Atlantic Salmon (Salmo salar)

Gill damage represents a significant challenge in the teleost fish aquaculture industry globally, due to the gill’s involvement in several vital functions and direct contact with the surrounding environment. To examine the local and systemic effects accompanying gill damage (which is likely to negatively affect gill function) of Atlantic salmon, we performed a field sampling to collect gill and liver tissue after several environmental insults (e.g., harmful algal blooms). Before sampling, gills were visually inspected and gill damage was scored; gill scores were assigned from pristine [gill score 0 (GS0)] to severely damaged gills (GS3). Using a 44K salmonid microarray platform, we aimed to compare the transcriptomes of pristine and moderately damaged (i.e., GS2) gill tissue. Rank Products analysis (5% percentage of false-positives) identified 254 and 34 upregulated and downregulated probes, respectively, in GS2 compared with GS0. Differentially expressed probes represented genes associated with functions including gill remodeling, wound healing, and stress and immune responses. We performed gill and liver qPCR for all four gill damage scores using microarray-identified and other damage-associated biomarker genes. Transcripts related to wound healing (e.g., neb and klhl41b) were significantly upregulated in GS2 compared with GS0 in the gills. Also, transcripts associated with immune and stress-relevant pathways were dysregulated (e.g., downregulation of snaclec 1-like and upregulation of igkv3) in GS2 compared with GS0 gills. The livers of salmon with moderate gill damage (i.e., GS2) showed significant upregulation of transcripts related to wound healing (i.e., chtop), apoptosis (e.g., bnip3l), blood coagulation (e.g., f2 and serpind1b), transcription regulation (i.e., pparg), and stress-responses (e.g., cyp3a27) compared with livers of GS0 fish. We performed principal component analysis (PCA) using transcript levels for gill and liver separately. The gill PCA showed that PC1 significantly separated GS2 from all other gill scores. The genes contributing most to this separation were pgam2, des, neb, tnnt2, and myom1. The liver PCA showed that PC1 significantly separated GS2 from GS0; levels of hsp70, cyp3a27, pparg, chtop, and serpind1b were the highest contributors to this separation. Also, hepatic acute phase biomarkers (e.g., serpind1b and f2) were positively correlated to each other and to gill damage. Gill damage-responsive biomarker genes and associated qPCR assays arising from this study will be valuable in future research aimed at developing therapeutic diets to improve farmed salmon welfare.

Salinity significantly affects intestinal microbiota and gene expression in striped catfish juveniles

In the present study, juvenile striped catfish (Pangasianodon hypophthalmus), a freshwater fish species, have been chronically exposed to a salinity gradient from freshwater to 20 psu (practical salinity unit) and were sampled at the beginning (D20) and the end (D34) of exposure. The results revealed that the intestinal microbial profile of striped catfish reared in freshwater conditions were dominated by the phyla Bacteroidetes, Firmicutes, Proteobacteria, and Verrucomicrobia. Alpha diversity measures (observed OTUs (operational taxonomic units), Shannon and Faith's PD (phylogenetic diversity)) showed a decreasing pattern as the salinities increased, except for the phylogenetic diversity at D34, which was showing an opposite trend. Furthermore, the beta diversity between groups was significantly different. Vibrio and Akkermansia genera were affected differentially with increasing salinity, the former being increased while the latter was decreased. The genus Sulfurospirillium was found predominantly in fish submitted to salinity treatments. Regarding the host response, the fish intestine likely contributed to osmoregulation by modifying the expression of osmoregulatory genes such as nka1a, nka1b, slc12a1, slc12a2, cftr, and aqp1, especially in fish exposed to 15 and 20 psu. The expression of heat shock proteins (hsp) hsp60, hsp70, and hsp90 was significantly increased in fish reared in 15 and 20 psu. On the other hand, the expression of pattern recognition receptors (PRRs) were inhibited in fish exposed to 20 psu at D20. In conclusion, the fish intestinal microbiota was significantly disrupted in salinities higher than 10 psu and these effects were proportional to the exposure time. In addition, the modifications of intestinal gene expression related to ion exchange and stressful responses may help the fish to adapt hyperosmotic environment. KEY POINTS: • It is the first study to provide detailed information on the gut microbiota of fish using the amplicon sequencing method. • Salinity environment significantly modified the intestinal microbiota of striped catfish. • Intestinal responses may help the fish adapt to hyperosmotic environment.

Comparative Transcriptomics of the Northern Quahog Mercenaria mercenaria and Southern Quahog Mercenaria campechiensis in Response to Chronic Heat Stress

The northern quahog (Mercenaria mercenaria) supports lucrative aquaculture industries in the USA. In the southeastern USA, aquacultured M. mercenaria faces increasing risks of summer die-offs from prolonged heat waves. We used a comparative transcriptomic approach to investigate the molecular responses of M. mercenaria and its southern congener, Mercenaria campechiensis, to controlled incremental heat stress over a 4-week period. Mercenaria were exposed to temperatures from 24 to 34 °C with 2.5 °C/week, after which, gill transcriptomes were de novo assembled and annotated. During the 4 weeks of chronic heat exposure, both species had the same survival rate (96%); M. mercenaria experienced body weight gain/loss depending on the originated hatcheries while M. campechiensis experienced an average net weight loss. The upregulated genes in both species included those in chaperone-mediated protein folding and regulation of cell death pathways, while the downregulated genes in both species involved in mRNA processing and splicing pathways. Compared to M. mercenaria, M. campechiensis appears to be more sensitive to prolonged heat stress as indicated by upregulating significantly more genes in coping with oxidative stress and in the protein degradation pathways, while downregulating some inhibitors of apoptosis. We discussed this finding within their ecological and evolutionary context. Our findings highlighted the potential vulnerability of the two quahogs, especially the southern quahog, to continued ocean warming.

Transcriptome analysis reveals potential key immune genes of Hong Kong oyster (Crassostrea hongkongensis) against Vibrio parahaemolyticus infection

Hong Kong oyster (Crassostrea hongkongensis) is one of the main species of economic shellfish cultivated in the coastal areas of southern China. The cultivation of this shellfish may be adversely impacted by Vibrio parahaemolyticus, a harmful pathogenic bacterium for many mariculture species, as it usually exists on the surface of Hong Kong oysters. Although previous studies have discovered that oysters rely on non-specific immune system to fight pathogen invasion, the genes corresponding to the complex immune system against Vibrio is still not fully elucidated. Therefore, we conducted a transcriptome analysis on the gill from Hong Kong oysters at two time points (i.e., 12 h and 24 h after V. parahaemolyticus or PBS challenge) to identify potential immune genes against V. parahaemolyticus infection. A total of 61779 unigenes with the average length of 1221 bp were obtained, and the annotation information of 39917 unigenes were obtained from Nr, SwissProt, KEGG and COG/KOG. After a pairwise comparison between V. parahaemolyticus or PBS challenge at the two time points, three groups of differentially expressed genes induced by V. parahaemolyticus were captured and analyzed. GO and KEGG analyses showed that multiple immune-related genes played an important role in pathogen infection, including HSP70, PCDP3 and TLR4. Furthermore, genes annotation indicated that LITAF, TNFSF10, Duox2 and big defensin family are also involved in immune regulation. Our study provides a reference for further exploration the molecular mechanism that defenses the pathogen infection regarding the identified immune-related genes in Hong Kong oysters.

Effect of Pandanus tectorius extract as food additive on oxidative stress, immune status, and disease resistance in Cyprinus carpio

The present study investigated the effect of Pandanus tectorius (PT) extract on Cyprinus carpio growth, antioxidant capacity, immunological and oxidative stress, immune-related gene expression, and resistance against pathogen challenge. Fish (average weight: 12.18 ± 0.32 g) were fed with diets containing various concentration (g kg^-1) of PT extract: 0 g (basal diet), 5 g [PT5], 10 g [PT10], 20 g [PT20], and 30 g [PT30] for 8 weeks. Our results revealed an increase (p < 0.05) in the final weight gain only in the PT20 (63.12 ± 1.4 g) group. Activity of liver antioxidant parameters such as catalase (CAT) (27.67 ± 1.12 U mg protein^-1), superoxide dismutase (SOD) (13.17 ± 0.428 U mg protein^-1), and glutathione peroxidase (GPx) (47.14 ± 1.47 U mg protein^-1) was highest in the PT20 group. Among the serum immunological parameters examined, lysozyme (37.45 ± 0.67 U mL^-1), alternative complement pathway (133.22 ± 1.92 U mL^-1), and phagocytic activities (25.68 ± 0.93%) were high (p < 0.05) in PT20, whereas there was no significant effect on serum immunoglobulin or total protein levels, compared to the control. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and malondialdehyde (MDA) levels were found to be lower (p < 0.05) in the PT20 and PT30 groups than those in the control. However, myeloperoxidase (MPO) levels were significantly higher (p < 0.05) in the PT20 and PT30 groups. Gene expression analysis revealed that mRNA expressions of antioxidant genes (SOD, CAT, nuclear factor erythroid 2-related factor 2) and anti-inflammatory cytokine (IL-10) genes were significantly upregulated in the PT10 - PT30 groups, except for the SOD gene in PT10. Conversely, the signalling molecule NF-κBp65 was downregulated in PT20 and PT30. Expression of Toll-like receptor 22 (TLR22) and hepcidin was significantly upregulated in PT20 and PT30, respectively. Fish in the PT20 group exhibited highest relative post-challenge survival (70.37%) against Aeromonas hydrophila challenge. The results of the present study suggest that dietary supplementation of P. tectorius extract at 20 g kg^-1 can significantly improve weight gain, serum antioxidant parameters, strengthen immunity, and increase the disease resistance of C. carpio. Therefore, P. tectorius extract could be exploited for its use as a food additive in aquaculture.

Nano-silica and magnetized-silica mitigated lead toxicity: Their efficacy on bioaccumulation risk, performance, and apoptotic targeted genes in Nile tilapia (Oreochromis niloticus)

Contamination of aquatic systems with heavy metals (HM) is of great concern owing to their deleterious impact on living organism. The current research is focused on application of silica particles with new functionalized properties (magnetic silica; SiMag or Nanoporous silica; SiNPs) and their efficacy to mitigate lead (pb) toxicity in Nile tilapia. One thousand fingerlings were distributed: two control groups (negative; without pb toxicity (NC) positive (with pb toxicity) and other four groups received two silica sources (SiMag or SiNPs) with two levels (400 and 600 mg/kg diet) for 56 days then exposed to pb for 30 days. Before toxicity exposure, maximum growth, and most improved feed conversion ratio and biochemical parameters were noticed with higher SiMag or SiNPs levels. Serum antioxidant enzymes and their transcriptional levels in muscle and liver were boosted in groups received SiMag or SiNPs. After toxicity exposure, hematological and antioxidants biomarkers maintained at adequate levels in SiMag or SiNPs. Prominent reduction of residual pb in gills, liver, kidney, and muscle was observed in SiNPs then SiMag groups. Interestingly, the maximum down-regulation of P450, caspase-3 and HSP-70 and MT were observed in groups received 600 mg/kg diet of SiMag or SiNPs. The higher level of P53 in liver and gills was detected in PC, inversely reduced in SiMag or SiNPs. Severity of the histopathological alterations in examined organs greatly reduced in groups received SiMag or SiNPs, unlike it were induced in PC group. In conclusion, higher SiMag or SiNPs levels not only mitigate negatives impact of pb toxicity in fish but also ensure its safety for human consumption.

Gene expression and functional analysis of different heat shock protein (HSPs) in Ruditapes philippinarum under BaP stress

Heat shock proteins (HSPs) are a class of highly conserved proteins which can protect cells against various types of stress. However, little information on the mechanism involved in the organic contaminants stress response of HSPs is available, especially in marine invertebrates. The present study was conducted to evaluate the responses of HSPs in clams (Ruditapes philippinarum) under Benzo[a] pyrene (BaP) exposure. The clams were exposed to BaP (concentrations: 0, 0.1, 1, 10 μg/L) for 15 days. 6 HSPs mRNA were classified, and the results of tissue distribution indicated that 4 HSPs gene expressed most in the digestive glands. The transcription level of 6 HSPs (HSP22-1, HSP22-2, HSP40A, HSP60, HSP70, HSP90) genes and the aryl hydrocarbon receptor signaling pathway-related genes, and detoxification system-related enzymes activities were analyzed at 0, 1, 3, 6, 10 and 15 days. The activities of phase II detoxification metabolic enzymes and signaling pathway related genes in clams were severely affected by BaP stress and presented significant difference. Our result suggested that HSPs were produced in the presence of BaP and participated in the process of detoxification metabolism to a certain extent. Additionally, the transcription of HSP40A gene may be used as a potential biomarker of BaP exposure due to its evident concentration- and time-dependent expression pattern. Overall, the study investigated the classification of HSPs in R. philippinarum, provided information about the expression profiles of various HSPs after BaP exposure and broadened the understanding mechanism of HSPs in detoxification defense system under PAHs stress in mollusks.

Concurrent changes in thermal tolerance thresholds and cellular heat stress response reveals novel molecular signatures and markers of high temperature acclimation in rainbow trout

The objective of this study was to better understand the molecular mechanisms which regulate acclimatory responses and thermal safety margins of rainbow trout (Oncorhynchus mykiss) at temperatures above physiological optimum. For this, we investigated the time course of changes in critical thermal tolerance thresholds and associated hepatic and renal transcript abundance of molecular markers related to cellular stress response, during high temperature acclimation. The experimental fish were initially acclimated to 17 °C and later exposed to a gradually raised elevated temperature regime (22 °C) for a period of 30 days. CT_max, CT_min and mRNA expression of candidate markers were examined before the thermal challenge (T₀) and over the time-course (days) of high temperature exposure (T₁, T₃, T₇, T₁₅ and T₃₀). With respect to organismal response, CT_max was significantly elevated at T₃, but the degree of gain in heat tolerance was not persistent. Contrarily, we observed a gradual loss in cold tolerance with highest CT_min estimate at T₃₀. Based on the time-course of mRNA expression, the studied markers could be categorized into those which were persistently elevated (hsp70a, hsp70b, hspa5, hsp90a, hsp90b, stip1 and serpinh1 in kidney and hsp90b in liver); those which concurred with changes in CT_min (hspbp1, hsp90b, stip1, gr1, hif1a, hyou1, tnfa and tlr5 in kidney); and those which concurred with changes in CT_max (hsp90a, serpinh1, tlr5 and lmo2 in liver). Apparently, transcriptional changes in kidney and liver reflected CT_min and CT_max trend, respectively. Expression profile of stip1 and tlr5 suggest that they are potential novel markers which could reflect thermal limits in rainbow trout. Hepatic metabolic markers were either initially elevated (alt, glud, g6pase1) or down-regulated at different time-points (ast2, gls1, fas, cpt1b, mtor), linked to gluconeogenesis and metabolic depression, respectively. Whereas, growth-axis markers showed no significant differences. Overall, this time-course analysis has revealed potential associations in organismal and tissue-specific cellular response to high temperature acclimation in a thermally sensitive coldwater ectotherm.

Effects of chitin from Daphnia similis and its derivative, chitosan on the immune response and disease resistance of white shrimp, Litopenaeus vannamei

Daphnia similis chitin and its derivative chitosan were prepared as immunostimulants to boost the immune response and determine the ability to control infectious disease caused by Vibrio alginolyticus in white shrimp, Litopenaeus vannamei. Three experimental diets supplemented with 0% chitin or chitosan (control) and 0.4% chitin or 0.4% chitosan were fed to shrimp for 56 days. Dietary inclusion of 0.4% chitosan accelerated shrimp growth compared to chitin and control. The survival and disease resistance of shrimp increased significantly when fed chitin and chitosan diets, after pathogenic injection, as indicated by the up-regulated immune responses in respiratory burst (RB), superoxide dismutase (SOD), and phagocytic activity (PA). There were no significant differences in the total haemocyte count (THC), phenoloxidase (PO)activity, and lysozyme (LYZ) activity among the groups. No significant differences were observed for prophenoloxidase system-related gene expressions among groups. However, shrimp fed chitin, and chitosan expressed significantly higher levels of antimicrobial proteins (penaeidin 3a, crustin, and anti-lipopolysaccharide factor 2) in the haemocytes than in control. The gene expressions of catalase and heat shock protein 70 increased in the hepatopancreas of shrimp fed chitosan diet compared to the chitin and control diet. The O-linked N-acetylglucosamine transferase (ogt) was significantly higher in the haemocytes of shrimp fed chitosan and chitin than the control, but ogt was only significantly higher in the hepatopancreas of shrimp fed chitosan. Dietary chitin and chitosan also showed positive effects on the transcription of peritrophin-like protein. These findings suggest that both chitin and chitosan from D. similis are efficacious at boosting the immunity of shrimp by preventing and controlling infectious diseases caused by Vibrio and have great potential to be used as a feasible immunostimulant that significantly contributes to the circular economy.

Dietary α-lipoic acid can alleviate the bioaccumulation, oxidative stress, cell apoptosis, and inflammation induced by lead (Pb) in Channa argus

This study aims to evaluate the effects of dietary α-lipoic acid (α-LA) on bioaccumulation, oxidative stress, apoptosis, and inflammation in Channa argus after 28 d of lead (Pb) exposure. A total of 300 fish were divided into five groups: the first group was the control group and the other four groups were exposed to waterborne Pb (800 ppb) and fed α-LA diets supplemented with 0, 300, 600, and 900 mg/kg. The results demonstrated that dietary α-LA effectively reduced the Pb accumulation in the liver, kidney, gill, intestine, and muscle of C. argus after exposure to Pb. Meanwhile, dietary α-LA reversed alterations in the biochemical parameters (Alanine aminotransferase (ALT), lactate dehydrogenase (LDH), aspartate aminotransferase (AST), blood urea nitrogen (BUN), cortisol (COR), and creatinine (CRE)) and immunity parameters (myeloperoxidase (MPO), complement 3 (C3), lysozyme (LYS), complement 4 (C4), C-reactive protein (CRP), and immunoglobulin M (IgM)) in the serum of fish caused by Pb. Pb-induced reduction of antioxidant enzyme activities (Catalase (CAT), glutathione reductase (GR), superoxide dismutase (SOD), glutathione (GSH), glutathione peroxidase (GSH-Px)) was inhibited by dietary α-LA. And malondialdehyde (MDA) and protein carbonyl (PC) content exhibited an opposite trend. Meanwhile, dietary supplemented with α-LA was found to relieve Pb-induced oxidative stress by downregulating Keap1 mRNA expression levels and upregulating the expression levels of CAT, nuclear factor erythroid 2-related factor 2 (Nrf2), GSH-Px, and Cu/Zn SOD. Furthermore, α-LA supplementation reversed Pb-induced upregulation of pro-inflammatory genes (interleukin (IL)-6, IL-1β, tumor necrosis factor α (TNF-α), and nuclear factor kappa B (NF-κB)), Pro-apoptotic genes (Bcl-2-associated X (Bax), caspase (Cas)-3, and tumor protein p53 (p53)) and Hsp70, and downregulation of anti-inflammatory genes (IL-10, inhibitor of κBα (IκBα), and transforming growth factor β (TGF-β)) and anti-apoptosis gene (B-cell lymphoma-2 (Bcl-2)). Overall, dietary α-LA supplementation could enhance the innate immunity and antioxidant capacity of fish, attenuating the Pb accumulation, and cell apoptosis after being exposed to Pb. Furthermore, dietary α-LA could relieve Pb-induced inflammatory response and oxidative stress of fish via regulating NF-κB and Nrf2 signaling, respectively.

Transcriptome analysis provides the first insight into the molecular basis of temperature plasticity in Banggai cardinalfish, Pterapogon kauderni

Banggai cardinalfish, Pterapogon kauderni, is a tropical fish listed as an endangered species by IUCN. Its distribution and survival condition are extremely limited, and the changes of living environment caused by global warming may seriously threaten its geographical distribution. In order to understand the survival temperature range and the potential mechanism of temperature plasticity of P. kauderni, transcriptome analysis was performed under five temperature conditions (18 °C, 22 °C, 26 °C, 30 °C and 34 °C). A total of 432,444,497 clean reads were obtained from the mix tissues of whole head, viscera (except intestine), and muscle. All clean data were spliced into 194,832 unigenes. Compared with 26 °C, 57, 107, 187 and 174 differentially expressed genes (DEGs) were obtained at 18 °C, 22 °C, 30 °C and 34 °C, respectively. Gene Ontology (GO) analysis showed the most highly enriched in the DEGs were cellular processes, binding, metabolic processes and biological regulation. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated circadian rhythm, protein processing in endoplasmic reticulum, influenza A and prion disease were significantly enriched. 47 genes that may be related to temperature stress were identified, such as Per1, MLP, IGFBP1, HSP70, HSP90α, HSPA4, DNAJB1, CALR. This is the first RNA-Seq study of P. kauderni. This information should be valuable for further targeted studies on temperature tolerance, thereby assisting the protection and development of P. kauderni.

Transcriptome analysis reveals the mechanism of alkalinity exposure on spleen oxidative stress, inflammation and immune function of Luciobarbus capito

Saline-alkali land is distributed all over the world, and it affects the economic development of fisheries. The alkalinity in water is related to the accumulation of carbonate, so the is generally higher. To understand how alkalinity impacts the immune response in Luciobarbus capito, we performed transcriptomic profiles for spleen, the immune organ of Luciobarbus capito which were underwent alkalinity exposure. Totally there are 47,727,954, 53,987,820 and 51,398,546 high quality clean reads obtained from the control groups, and 46,996,982, 49,650,460 and 45,964,986 clean reads from the alkalinity exposure groups. Among them, 611 genes were differently expressed, including 534 upregulated and 77 down-regulated genes. The identified genes were enriched using databases of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). It was found that differentially expressed genes in Luciobarbus capito spleen tissue were enriched into 14 GO pathways, and differentially expressed genes in Luciobarbus capito spleen were enriched into 25 corresponding KEGG pathways under alkalinity stress. Inflammation and immune function genes and pathways were identified and validated by quantitative real-time RT-PCR. Our results showed that alkalinity exposure leads to inflammation and immunoregulation in spleen of Luciobarbus capito. These results provide new insights for unveiling the biological effects of alkalinity in Luciobarbus capito.

Histopathological damage and stress- and immune-related genes' expression in the intestine of common carp, Cyprinus carpio exposed to copper and polyvinyl chloride microparticle

The present study aimed at assessing the singular and combined effects of water copper and polyvinyl chloride microplastic (MPVC) on intestinal copper accumulation, histopathological damage, and stress-/immune-related genes' expression in common carp, Cyprinus carpio. Four groups of fish were maintained in triplicate: control (kept in clean water), Cu (exposed to 0.25 mg/L of copper), MPVC (exposed to 0.5 mg/L of MPVC), and Cu-MPVC (exposed to 0.25 mg/L of copper + 0.5 mg/L of MPVC). After 14-day exposure, the fish of Cu and Cu-MPVC treatments exhibited significantly higher intestinal copper contents, compared to the fish of control and MPVC treatments. In this regard, the Cu-MPVC fish had significantly higher copper content than the Cu fish. Exposure to copper and/or MPVC significantly upregulated the intestinal heat shock protein 70 (hsp70), cytochrome P450 family 1 subfamily A member 1 (cyp1a1), lysozyme (lys), defensin (def), mucin 2 (muc2), and mucin 5 (muc5) expression. The highest expression of hsp70, cyp1a1, lys, and def was related to Cu-MPVC treatment; whereas, the highest expression of muc2 and muc5 was observed in Cu and MPVC treatments. Exposure to copper and/or MPVC induced intestinal damage, which Cu-MPVC fish exhibited the highest severity. The present study revealed that exposure to copper and/or MPVC causes intestinal histopathological damage and upregulation in stress- and immune-related genes' expression. The most serious effects were observed in Cu-MPVC treatment that might be due to additive effects of copper and MPVC and/or higher copper accumulation in this treatment.

Characterization and function analysis of Epinephelus coioides Hsp40 response to Vibrio alginolyticus and SGIV infection

Heat shock protein 40 (Hsp40), a member of Heat shock proteins (Hsps) family, plays a crucial role in regulation of cell proliferation, survival and apoptosis in mammals. In this study, Hsp40, EcHsp40, was identified from Epinephelus coioides, an economically important marine-cultured fish in China and Southeast Asian counties. The full length of EcHsp40 was 2236 bp in length containing a 1026 bp open reading frame (ORF) encoding 341 amino acids, with a molecular mass of 37.88 kDa and a theoretical pI of 9.09. EcHsp40 has two conserved domains DnaJ and DnaJ_C. EcHsp40 mRNA was detected in all tissues examined, and the expression was significantly up-regulated response to challenged with Vibrio alginolyticus or Singapore grouper iridovirus (SGIV), one of the important pathogens of marine fish. EcHsp40 was distributed in both the cytoplasm and nucleus, over-expression of EcHsp40 can inhibit the activity of nuclear factor-κB (NF-κB) and activator protein-1 (AP-1), significantly promote SGIV-induced apoptosis, intracellular caspase-3 activity and viral replication, suggesting that the EcHsp40 may play an important role in pathogenic stimulation.

Functional Feeds to Tackle Meagre (Argyrosomus regius) Stress: Physiological Responses under Acute Stressful Handling Conditions

Marine algae are recognised sources of bioactive compounds that have attracted great interest as nutritional supplements for aquaculture fish. Intensive rearing conditions often expose fish to husbandry-related stressors, rendering fish more susceptible to disease and reducing production yields. The present work evaluated the potential of two marine algae extracts (Fucus vesiculosus and Nannochloropsis gaditana) as nutritional supplements to mitigate stress effects in meagre (Argyrosomus regius) exposed to an acute handling stress (AS). A plant-based diet was used as a control, and three other diets were prepared, which were similar to the control diet but supplemented with 1% of each algal extract or a combination of the two extracts (0.5% each). The effects of supplemented diets on stress biomarkers, antioxidant enzyme activities, and immune response were analysed in fish exposed to AS after 4 weeks of feeding. Supplemented diets did not affect growth performance but the inclusion of F. vesiculosus promoted higher feed efficiency, as compared to the control group. Dietary algal extracts supplementation reduced plasma glucose levels, increased white blood cell counts, and reduced the expression of pro-inflammatory genes when compared with the control. N. gaditana supplementation led to a reduction in hepatic antioxidant enzyme activity and glutathione levels, while F. vesiculosus supplementation increased muscle glutathione reductase activity and reduced lipid peroxidation. These findings support the potential of algal extracts as nutraceuticals in aquafeeds to enhance the ability of fish to cope with husbandry-related stressful conditions and ultimately improve fish health and welfare.

Characterization, Stress Response and Functional Analyses of Giant River Prawn (Macrobrachium rosenbergii) Glucose-Regulated Protein 78 (Mr-grp78) under Temperature Stress and during Aeromonas hydrophila Infection

Simple Summary

Glucose-regulated protein 78 (grp78) is classified as a member of the Hsp70 subfamily. This protein functions as a key factor in signal transduction associated with the unfolded protein response (UPR) in the endoplasmic reticulum (ER) during cellular stress and protects against cell damage caused by toxic chemicals, oxidative stress, Ca²⁺ depletion, programmed cell death and various infectious conditions. To investigate this crucial mechanism in giant river prawn (Macrobrachium rosenbergii), we analyzed the biological function of prawn grp78 at the molecular level in this study. The regulation of this gene was intensively analyzed under normal bacterial infection and heat/cold-shock inductions. A functional analysis of this gene under heat and infectious stress conditions was performed by gene knockdown. The information obtained in the current study clearly indicates the crucially significant roles of grp78 in the cellular stress responses of the target experimental animal under various stress conditions.

Abstract

The endoplasmic reticulum (ER) is an organelle important for several functions of cellular physiology. This study identified the giant river prawn’s glucose-regulated protein 78 (Mr-grp78), which is important for ER stress mechanisms. Nucleotide and amino acid analyses of Mr-grp78, as compared with other species, revealed the highest similarity scores with the grp78 genes of crustaceans. An expression analysis by quantitative RT-PCR indicated that Mr-grp78 was expressed in all tissues and presented its highest expression in the ovary (57.64 ± 2.39-fold), followed by the gills (42.25 ± 1.12), hindgut (37.15 ± 2.47), thoracic ganglia (28.55 ± 2.45) and hemocytes (28.45 ± 2.26). Expression analysis of Mr-grp78 mRNA levels under Aeromonas hydrophila induction and heat/cold-shock exposure was conducted in the gills, hepatopancreas and hemocytes. The expression levels of Mr-grp78 in these tissues were highly upregulated 12 h after bacterial infection. In contrast, under heat- and cold-shock conditions, the expression of Mr-grp78 was significantly suppressed in the gills at 24–96 h and in the hepatopancreas at 12 h (p < 0.05). A functional analysis via Mr-grp78 gene knockdown showed that Mr-grp78 transcription in the gills, hepatopancreas and muscle strongly decreased from 6 to 96 h. Furthermore, the silencing of this gene effectively increased the sensitivity of the tested prawns to heat- and pathogenic-bacterium-induced stress. The results of this study clearly demonstrate the significant functional roles of Mr-grp78 in response to both temperature and pathogen treatments.

Molecular Characterization and Defense Functions of the Nile Tilapia (Oreochromis niloticus) DnaJ B9b and DnaJ C3a Genes in Response to Pathogenic Bacteria under High-Temperature Stress Conditions

DnaJ proteins or heat shock protein 40s (HSP40s) form one of the largest heat shock protein families. In this study, 2 cDNAs encoding Nile tilapia (Oreochromis niloticus) DnaJ proteins (On-DnaJ B9b and On-DnaJ C3a) were successfully cloned and characterized. The structures and organizations of these two genes are first reported in the present study. On-DnaJ B9b is approximately 2.1 kb long and contains 2 exons and 1 intron, while On-DnaJ C3a is approximately 12 kb long and contains 12 exons and 11 introns. Under normal conditions, On-DnaJ B9b mRNA is highly expressed in gonad and trunk kidney tissues, while On-DnaJ C3a transcripts are abundantly expressed in gills, intestine, liver, and trunk kidney tissues. Following pathogenic infections, the expression of both genes is induced in the liver, spleen and head kidney tissues of Nile tilapia that were infected with two virulent pathogenic bacteria, Streptococcus agalactiae and Flavobacterium columnare. Silencing of these two genes was first carried out, and the results clearly indicated their crucial roles under both heat and bacterial stress conditions. The fundamental knowledge obtained from this study indicates the characteristic basic biofunctions of heat shock proteins in the regulation of intracellular proteins during infection, which involve preventing protein aggregation, promoting protein refolding, and activating unfolded protein degradation.

The effect of Roundup on embryonic development, early foxr1 and hsp70 gene expression and hatching of common carp (Cyprinus carpio L.)

The effects of herbicide Roundup (based on glyphosate) on the embryonic development, survival and hatching of common carp (Cyprinus carpio L.) larvae and alteration in foxr1 and hsp70 gene expression were determined. The eggs (obtained from 6 females) were fertilised and incubated in water containing 0; 1 or 10 μl L^-1 of Roundup formulation. During early embryonic development (24 and 48 h post-fertilisation - hpf), Roundup caused a statistically important decrease in the embryonic survival rate of common carp. Moreover, retardation of the hatching rate was observed in the group treated with the higher concentration of Roundup at 81 to 99 hpf. At the end of the experiment (99 hpf), an important increase in number of deformed larvae was observed in both groups treated with Roundup in comparison to the control group (52.06; 16.02 and 5.08%, respectively). Significant differences in transcript of the gene foxr1 were found in Roundup-intoxicated groups in comparison to the controls. In the case of hsp70 transcripts, no important changes in exposed groups were observed. These results showed that even small, environmentally relevant amount of Roundup present in the aquatic environment is able to affect the early life stages of common carp and change the transcripts of foxr1, which may have an adverse effect on the later proper development of the reproductive system.

Toxic effects of hexavalent chromium (Cr6+) on bioaccumulation, apoptosis, oxidative damage and inflammatory response in Channa asiatica

The objective of this study was to evaluate the toxic effects of Cr⁶⁺ on bioaccumulation, digestion, immunity, oxidative stress, apoptosis and inflammation-related genes in Channa asiatica. The fish was exposed to waterborne Cr⁶⁺ concentrations (0, 0.5, 1.0 and 2.0 mg/L) for 28 and 56 days. Our results demonstrated that the accumulation of Cr⁶⁺ in tissues increased in a concentration-dependent manner, and the content in tissue was liver > gill > gut > muscle. Meanwhile, Cr⁶⁺ exposure led to a remarkable suppression of digestion, immunity and antioxidant capacity in C. asiatica. Inversely, MDA and PC content were positively correlated with Cr⁶⁺ exposure concentration. Furthermore, the expression of genes went up with the increase of waterborne Cr⁶⁺ concentration. Among them, HSP90, NF-κB and TNF-α have a sharp increase. These results elucidate that waterborne Cr⁶⁺ exposure may induce bioaccumulation, inhibit digestion and immunity, promote oxidative stress and up-regulate the expression of apoptosis and inflammation-related genes in C. asiatica.

Sex steroid dynamics and mRNA transcript profiles of growth- and development-related genes during embryogenesis following induced follicular maturation in European eel

Hormones and mRNA transcripts of maternal origin deposited in the egg may affect early embryonic development in oviparous species. These hormones include steroids, such as estradiol-17β (E2), testosterone (T), 11-ketotestosterone (11-kt), 17α,20ß-dihydroxy-4-pregnen-3-one (DHP), and cortisol, which also play an important role in fish reproduction. In European eel, Anguilla anguilla, which does not reproduce naturally in captivity, vitellogenesis in female broodstock is commonly induced by administration of salmon or carp pituitary extract (PE) as an exogenous source of gonadotropins, while follicular maturation is stimulated by a priming dose of PE followed by provision of DHP as a maturation inducing hormone. In this regard, the main purpose of the present study was to evaluate effects of induced follicular maturation on reproductive success in European eel, focusing on maternal transfer and dynamics of steroids and mRNA transcripts of growth- and development-related genes throughout embryogenesis. The results showed that maternal blood plasma concentrations of E2, T and DHP were reflected in the unfertilized eggs. Moreover, a negative relationship between concentrations of E2 and DHP in eggs and embryos and quality parameters measured as fertilization success, cleavage abnormalities, embryonic survival, and hatch success was found. Concomitant mRNA transcript abundance analysis including genes involved in stress response (hsp70, hsp90), somatotropic axis (gh, igf1, igf2a, igf2b), lipid (cpt1a, cpt1b, pigf5) and thyroid metabolism (dio1, dio2, dio3, thrαb, thrβa, thrβb) varied among unfertilized egg batches. For the majority of genes, mRNA abundance increased during the maternal-to-zygotic transition in connection to activation of the transcription of the embryos own genome. mRNA abundance of dio1, cpt1a and cpt1b throughout embryogenesis was related to embryonic developmental competence. Notably, mRNA abundance of dio3 was positively associated with E2 concentrations, while the mRNA abundance of thrαb was negatively related to T concentrations in the unfertilized eggs, which may suggest an interaction between the thyroid and steroid hormone systems. Altogether, maternal plasma concentrations of E2 and DHP were reflected in the eggs, with high concentrations of these steroids in the eggs being negatively associated with embryonic developmental competence. Additionally, high transcript levels of two of the investigated genes (dio1, cpt1b) were positively associated with embryonic developmental competence. This study reveals maternal transfer of steroids and mRNA transcripts to the eggs, which may be significant contributors to the variability in embryonic survival observed in European eel captive reproduction.

Transcriptome and co-expression network analyses reveal the regulatory pathways and key genes associated with temperature adaptability in the yellow drum (Nibea albiflora)

The yellow drum (Nibea albiflora) is an important marine economy fish, that is widely distributed in the coastal waters of the Northwest Pacific. To understand the molecular regulatory mechanism of the yellow drum under temperature stress, transcriptome analysis was performed under five temperature conditions (10 °C, 15 °C, 20 °C, 24 °C, 28 °C) in the present study. Compared with 20 °C, 163, 401, 276, and 372 differentially expressed genes (DEGs) were obtained at 10 °C, 15 °C, 24 °C and 28 °C, respectively. Gene Ontology (GO) analysis indicated that the DEGs were mainly involved in cellular processes, metabolic processes, catalytic activity, membrane and binding. Meanwhile, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the temperature adaptive regulation of the yellow drum was mainly involved in signal transduction, metabolism, genetic information and protein processing. Weighted gene co-expression network analysis (WGCNA) showed that HMGB1, STAT4, Noct, C1q and CRT may be the key hub genes in the response of the yellow drum to temperature stress. In addition, 20 genes that may be associated with temperature stress were identified based on comparative analysis between the KEGG enrichment and the WGCNA results. Ten DEGs were selected for further validation using quantitative real-time PCR (qRT-PCR), and the results were consistent with the RNA-seq data. This study explored the transcriptional patterns of the yellow drum under temperature stress and provided fundamental information on the temperature adaptability of this species.

The impact of acute cold water stress on blood parameters, mortality rate and stress-related genes in Oreochromis niloticus, Oreochromis mossambicus and their hybrids

This study aims to evaluated the response of Oreochromissp. to cold stress. Two experiments were conducted involving a total of 1080 juvenile Oreochromis niloticus, O. mossambicus, O. niloticus♂ × O.mossambicus♀=F1♂ × O.mossambicus ♀ (Hybrid 1; H1) and O. mossambicus♂ × O. niloticus♀ (Hybrid 2; H2). In the 1st experiment, fish were exposed to cold water (12 °C) for 24 h and then hematological parameters, serum biochemical variables, innate immune responses, antioxidant status, and liver gene expression responses (hsp70, hsp27, hsp90, hsp40, cat, sod, eef1a1 and calreticulin) were analyzed. Hematological and serum biochemical responses involved species-specific differences. At optimal temperatures (28 °C), respiratory burts activity (RBA) and myeloperoxidase (MPO) values of H1, H2 and O. mossambicus were significantly higher than O. niloticus (p< 0.05). While the RBAvalue of O. mossambicus decreased after exposure to cold water (p< 0.05), lysozyme activities of O. niloticus and H2 and MPO activities of all experimental fish increased significantly (p< 0.05). At control conditions (28 °C), cortisol levels were found to be higher in O. mossambicus than in H1 and O. niloticus (p< 0.05). A significant increase in cat and sod transcripts was observed in liver of fish being very pronounced in O. mossambicus and H2. The highest up-regulation was observed for hsp70 target where the lowest but significant up-regulation was observed for hsp90 gene. In 2nd experiment, water temperature was gradually decrease from 28 °C to 12 °C (average, 1 °C/1 h).Survival rates of H1 and H2 were found to be different compared to O. mossambicus and O. niloticus (p< 0.05) after 20 days of cold water challenge.O. mossambicus was the most cold-sensitive group, followed by the H2, H1 and O. niloticus. Our data should be carfully considered in view of the possible physiological and anti-stressor responses being species-specific in fish.

Thermal tolerance, metabolic scope and performance of meagre, Argyrosomus regius, reared under high water temperatures

This article reports on the thermal tolerance, metabolic capacity and performance of juvenile meagre (Argyrosomus regius) reared under three high water temperatures (24, 29 and 34 °C) for three months. The analysis includes the thermal effects on the growth performance, metabolism and physiology of meagre, including a range of molecular, haematological, metabolic, enzymatic and hormonal indicators, as well as the effects on the proximate composition and ingestion speed. Meagre performs best between 24 and 29 °C while the temperature of 34 °C is very close to the upper end of its temperature tolerance range. At 34 °C meagre exhibits a poor growth performance and physiological status, increased blood clotting, high mortality rates and a diminished capacity for aerobic metabolism, as indicated by its low aerobic scope (129 mg kg^-1 h^-1). Meagre may tolerate short exposures to high temperatures after sufficient acclimation (Critical thermal maximum of 37.5 °C after acclimation to 29 °C) but its overall performance declines under prolonged exposure, suggesting that this emerging aquaculture species may be vulnerable to global warming. Our work corroborates previous findings on the thermal preferences of the species, identifies critical biological thresholds, and provides insights into the effects of prolonged exposure to high temperature regimes.

Bioflocs attenuate Mn-induced bioaccumulation, immunotoxic and oxidative stress via inhibiting GR-NF-κB signalling pathway in Channa asiatica

Manganese (Mn) is a relatively common element in aquatic ecosystems and can be bio-concentration, but the mechanism of manganese poisoning on fish health is unclear. Here, this study's objective was to evaluate the potential mechanisms of bioflocs in ameliorating Mn-induced toxicity in Channa asiatica. Three hundred sixty juveniles were randomly divided into 12 tanks. Four C:N ratios in triplicate tanks were tried: C/N = 7.6:1 with a commercial diet (control), C/N 10:1, C/N 15:1 and C/N 20:1, and the bio-accumulation, immunotoxic, oxidative stress, GR-NF-κB related genes expression and intestinal histomorphology were assessed in three different periods after Mn exposure (0 h, 48 h and 96 h). The results showed that bioflocs had a significant protective effect on Mn poisoning by preventing alterations in bio-accumulation levels, LSZ, AKP, C3, C4 and IgM, of which the C/N 15:1 group had the best relief effect. Furthermore, bioflocs also assisted in the recovery of liver T-SOD, CAT, GPX and T-AOC levels while decreasing the content of MDA. Moreover, C/N 15:1 group significantly down-regulated the expression level of NF-κB, TNF-α, IL-1β and IL-8 and up-regulated significantly IκBα, GR, HSP70 and HSP90 expression levels considerably (P < 0.05). From the intestinal section, the C/N 15:1 group resistance was the best one, and there was no difference between C/N 20:1 group and control group. These results revealed that administration of bioflocs (C/N 15:1) has the potential to combat Mn toxicity in C. asiatica, and the specific pathway may be GR-NF-κB.

Ozone nanobubble treatments improve survivability of Nile tilapia (Oreochromis niloticus) challenged with a pathogenic multi-drug-resistant Aeromonas hydrophila

A rapid increase in multi-drug-resistant (MDR) bacteria in aquaculture highlights the risk of production losses due to diseases and potential public health concerns. Previously, we reported that ozone nanobubbles (NB-O₃ ) were effective at reducing concentrations of pathogenic bacteria in water and modulating fish immunity against pathogens; however, multiple treatments with direct NB-O₃ exposures caused alterations to the gills of exposed fish. Here, we set up a modified recirculation system (MRS) assembled with an NB-O₃ device (MRS-NB-O₃ ) to investigate whether MRS-NB-O₃ (a) were safe for tilapia (Oreochromis niloticus), (b) were effective at reducing bacterial load in rearing water and (c) improved survivability of Nile tilapia following an immersion challenge with a lethal dose of MDR Aeromonas hydrophila. The results showed no behavioural abnormalities or mortality of Nile tilapia during the 14-day study using the MRS-NB-O₃ system. In the immersion challenge, although high bacterial concentration (~2 × 10⁷  CFU/ml) was used, multiple NB-O₃ treatments in the first two days reduced the bacteria between 15.9% and 35.6% of bacterial load in water, while bacterial concentration increased from 13.1% to 27.9% in the untreated control. There was slight up-regulation of non-specific immune-related genes in the gills of the fish receiving NB-O₃ treatments. Most importantly, this treatment significantly improved survivability of Nile tilapia with relative percentage survival (RPS) of 64.7% - 66.7% in treated fish and surviving fish developed specific antibody against MDR A. hydrophila. In summary, the result suggests that NB-O₃ is a promising non-antibiotic approach to control bacterial diseases, including MDR bacteria, and has high potential for application in recirculation aquaculture system (RAS).

Size-dependent effects of microplastic on uptake, immune system, related gene expression and histopathology of goldfish (Carassius auratus)

Todays, with the industrialization of human societies, pollution of aquatic ecosystems with plastics derivatives are a serious concern, affecting the life of their organisms. The present study was conducted to investigate the size effects of micro-plastic, polystyrene on some physiological lesions of the goldfish, Carassius auratus. Fish were exposed to two sizes (0.25 and 8 μm) polystyrene at different environmentally relevant concentrations. The exposure trial was done in two steps. First, fish exposed to a stable concentration of 300 mg/L polystyrene for 168 h. Gill, intestine, and liver tissues were sampled every 24 h to investigate the accumulation of polystyrene. Then, fish were exposed in three replicates to 0 (control), 0.05, 0.5, and 5 mg/L polystyrene in two sizes of 0.25 and 8 μm for 28 days. After the exposure period, gill, liver, and intestine tissues were sampled for histological study, also, serum samples were collected for biochemical assays. Fluorescent microscope observations confirmed the accumulation of polystyrene in tissue samples with time. In addition, histological lesions were found in the liver, intestine, and gill of the exposed fish. The severity of lesions showed a size and dose-dependent pattern. Polystyrene induced the antioxidant system of exposed fish through elevating the levels of SOD and CAT activity and significant difference in expression of antioxidant related genes (CAT, SOD and HSP70). In conclusion, the results of the present study confirmed the toxic effects of microplastic, polystyrene on goldfish.

Acute Hepatopancreatic Necrosis Disease (AHPND): Virulence, Pathogenesis and Mitigation Strategies in Shrimp Aquaculture

Shrimp, as a high-protein animal food commodity, are one of the fastest growing food producing sectors in the world. It has emerged as a highly traded seafood product, currently exceeding 8 MT of high value. However, disease outbreaks, which are considered as the primary cause of production loss in shrimp farming, have moved to the forefront in recent years and brought socio-economic and environmental unsustainability to the shrimp aquaculture industry. Acute hepatopancreatic necrosis disease (AHPND), caused by Vibrio spp., is a relatively new farmed penaeid shrimp bacterial disease. The shrimp production in AHPND affected regions has dropped to ~60%, and the disease has caused a global loss of USD 43 billion to the shrimp farming industry. The conventional approaches, such as antibiotics and disinfectants, often applied for the mitigation or cure of AHPND, have had limited success. Additionally, their usage has been associated with alteration of host gut microbiota and immunity and development of antibiotic resistance in bacterial pathogens. For example, the Mexico AHPND-causing V. parahaemolyticus strain (13-306D/4 and 13-511/A1) were reported to carry tetB gene coding for tetracycline resistance gene, and V. campbellii from China was found to carry multiple antibiotic resistance genes. As a consequence, there is an urgent need to thoroughly understand the virulence mechanism of AHPND-causing Vibrio spp. and develop novel management strategies to control AHPND in shrimp aquaculture, that will be crucially important to ensure food security in the future and offer economic stability to farmers. In this review, the most important findings of AHPND are highlighted, discussed and put in perspective, and some directions for future research are presented.

Comparative transcriptome analysis reveals changes in gene expression in sea cucumber (Holothuria leucospilota) in response to acute temperature stress

Ambient temperature is an important abiotic factor that influences growth performance and physiological functions in sea cucumbers. To understand the molecular responses of the sea cucumber Holothuria leucospilota to acute temperature stress, we performed a de novo transcriptome analysis of body wall tissue from H. leucospilota exposed to 2 hoursh of acute heat (35 ± 1 °C) and cold stress (15 ± 1 °C). A total of 99,015 unigenes were obtained after assembly of the sequenced reads. Compared with a control group maintained at 25.0 ± 1 °C, 1169 differentially expressed unigenes (DEGs) were identified after heat stress, 781 were up-regulated and 388 were down-regulated. After cold stress, 1464 DEGs were identified; 900 were up-regulated and 564 were down-regulated. The annotation of DEGs revealed that heat shock proteins play important roles in protecting H. leucospilota from high temperature stress. Furthermore, KEGG pathway enrichment analysis showed that the categories: "Ribosome" and "Protein processing in endoplasmic reticulum" were strongly affected by heat stress. These two pathways are associated with biosynthesis and processing of proteins, and refolding of misfolded proteins. The lipid metabolism pathways "Sphingolipid metabolism" and "Ether lipid metabolism", were affected by cold stress. The RNA-Seq results for eight selected DEGs were verified the expression by quantitative real-time PCR analysis. Our results will improve the understanding of the molecular response mechanisms of H. leucospilota to ambient temperature stress.

Functional and Stress Response Analysis of Heat Shock Proteins 40 and 90 of Giant River Prawn (Macrobrachium rosenbergii) under Temperature and Pathogenic Bacterial Exposure Stimuli

The aims of this research were to perform molecular characterization and biofunctional analyses of giant river prawn Hsp40 and Hsp90 genes (Mr-hsp40 and Mr-hsp90) under various stress conditions. Comparisons of the nucleotide and amino acid sequences of Mr-hsp40 and Mr-hsp90 with those of other species showed the highest similarity scores with crustaceans. Under normal conditions, expression analysis using quantitative real-time RT-PCR (qRT-PCR) indicated that Mr-hsp40 was highly expressed in the gills and testis, and Mr-hsp90 expression was observed in all tissues, with the highest expression in the ovary. The expression patterns of Mr-hsp40 and Mr-hsp90 transcripts under Aeromonas hydrophila challenge and heat-cold shock conditions were examined in gills, the hepatopancreas and hemocytes, at 0, 3, 6, 12, 24, 48 and 96 h by qRT-PCR. Under bacterial challenge, Mr-hsp40 displayed variable expression patterns in all tissues examined during the tested periods. In contrast, upregulated expression of Mr-hsp90 was quickly observed from 3 to 12 h in the gills and hepatopancreas, whereas obviously significant upregulation of Mr-hsp90 was observed in hemocytes at 12-96 h. Under temperature shock conditions, upregulation of Mr-hsp40 expression was detected in all tested tissues, while Mr-hsp90 expression was quickly upregulated at 3-48 h in all tissues in response to 35 °C conditions, and conditions of 35 and 25 °C stimulated its expression in gills and the hepatopancreas at 12 and 48 h, respectively. Silencing analyses of these two genes were successfully conducted under normal, high-temperature (35 °C) and A. hydrophila infection conditions. Overall, knockdown of Mr-hsp40 and Mr-hsp90 effectively induced more rapid and higher mortality than in the PBS control and GFP induction groups in temperature and infectious treatments. Evidence from this study clearly demonstrated the significant functional roles of Mr-hsp40 and Mr-hsp90, which are crucially involved in cellular stress responses to both temperature and pathogenic bacterial stimuli.

The Atlantic salmon's stress- and immune-related transcriptional responses to moderate hypoxia, an incremental temperature increase, and these challenges combined

The marine environment is predicted to become warmer, and more hypoxic, and these conditions may negatively impact the health and survival of coastal fish species, including wild and farmed Atlantic salmon (Salmo salar). Thus, we examined how: (1) moderate hypoxia (∼70% air saturation) at 12°C for 3 weeks; (2) an incremental temperature increase from 12°C to 20°C (at 1°C week-1) followed by 4 weeks at 20°C; and (3) treatment "2" combined with moderate hypoxia affected transcript expression in the liver of post-smolts as compared to control conditions (normoxia, 12°C). Specifically, we assessed the expression of 45 genes related to the heat shock response, oxidative stress, apoptosis, metabolism and immunity using a high-throughput qPCR approach (Fluidigm Biomark™ HD). The expression profiles of 27 "stress"-related genes indicated that: (i) moderate hypoxia affected the expression of several stress genes at 12°C; (ii) their expression was impacted by 16°C under normoxic conditions, and this effect increased until 20°C; (iii) the effects of moderate hypoxia were not additive to those at temperatures above 16°C; and (iv) long-term (4 weeks) exposure to 20°C, with or without hypoxia, resulted in a limited acclimatory response. In contrast, the expression of 15 immune-related genes was not greatly affected until temperatures reached 20°C, and this effect was particularly evident in fish exposed to the added challenge of hypoxia. These results provide valuable information on how these two important environmental factors affect the "stress" physiology and immunology of Atlantic salmon, and we identify genes that may be useful as hypoxia and/or temperature biomarkers in salmonids and other fishes.

Bioflocs attenuates lipopolysaccharide-induced inflammation, immunosuppression and oxidative stress in Channa argus

The regulation of C/N in aquaculture water is an important means of environmental regulation, of which the most common is bioflocs technology (BFT). Here, an eight-week feeding experiment and a lipopolysaccharide (LPS) challenge test were proceed to investigate the growth, oxidative stress, immunosuppression and GR-NF-κB related genes expression of Channa argus rearing in the BFT. Four groups were set, the control group was a basic diet (C/N = 7.6:1), and the other three groups were adjusted by glucose, which was C/N 10: 1, C/N 15: 1 and C/N 20:1, respectively. And we detected the two-stage test indexes of C. argus before and after the LPS challenge. The results showed that the bioflocs of C/N 15:1 group significantly (P < 0.05) promoted the growth performance. Similarly, the trend of immune enzyme activity was the same before and after LPS challenge, but decreased after challenge (except AKP and IgM). The best group is still treatment C/N 15:1. Liver and intestine SOD, CAT, GPX, ASA and T-AOC levels of juveniles in treatment C/N 15:1 were markedly increased (P < 0.05) compared to control before and after the LPS challenge. Simultaneously, the content of MDA in control group was considerably higher than that in treatment C/N 15:1 (P < 0.05). Furthermore, C/N 15:1 group significantly down-regulated the expression level of pro-inflammatory factors (NF-κB, TNF-α, IL-1β and IL-8), and up-regulated IκBα, GR, HSP70 and HSP90 expression levels considerably (P < 0.05). Also, intestinal morphology appeared injury in control group, while intestinal integrity was better in treatment C/N 10:1 and C/N 15:1 after challenge. Taken together, these upshot indicated that bioflocs could enhance growth and alleviate C. argus from LPS-induced oxidative stress, immunosuppression and inflammation through restraining GR-NF-κB signaling pathway. The best C/N ratio for alleviating LPS is 15:1.

Temperature increase and its effects on fish stress physiology in the context of global warming

The capacity of fishes to cope with environmental variation is considered to be a main determinant of their fitness and is partly determined by their stress physiology. By 2100, global ocean temperature is expected to rise by 1-4°C, with potential consequences for stress physiology. Global warming is affecting animal populations worldwide through chronic temperature increases and an increase in the frequency of extreme heatwave events. As ectotherms, fishes are expected to be particularly vulnerable to global warming. Although little information is available about the effects of global warming on stress physiology in nature, multiple studies describe the consequences of temperature increases on stress physiology in controlled laboratory conditions, providing insight into what can be expected in the wild. Chronic temperature increase constitutes a physiological load that can alter the ability of fishes to cope with additional stressors, which might compromise their fitness. In addition, rapid temperature increases are known to induce acute stress responses in fishes and might be of ecological relevance in particular situations. This review summarizes knowledge about effects of temperature increases on the stress physiology of fishes and discusses these in the context of global warming.