Modulation of the immune system of fish by their environment

Vitamin C as a functional enhancer in the non-specific immune defense, antioxidant capacity and resistance to low-temperature stress of juvenile mud crab, Scylla paramamosain

This experiment was conducted to explore the effects of dietary vitamin C supplementation on non-specific immune defense, antioxidant capacity and resistance to low-temperature stress of juvenile mud crab (Scylla paramamosain). Mud crabs with an initial weight of 14.67 ± 0.13 g were randomly divided into 6 treatments and fed diets with 0.86 (control), 44.79, 98.45, 133.94, 186.36 and 364.28 mg/kg vitamin C, respectively. The experiment consisted of 6 treatments, each treatment was designed with 4 replicates and each replicate was stocked with 8 crabs. After 42 days of feeding experiment, 2 crabs were randomly selected from each replicate, and a total of 8 crabs in each treatment were carried out 72 h low-temperature challenge experiment. The results showed that crabs fed diets with 186.36 and 364.28 mg/kg vitamin C significantly improved the activities of alkaline phosphatase (AKP) and acid phosphatase (ACP) in hemolymph and hepatopancreas (P < 0.05). Crabs fed diet with 133.94 mg/kg vitamin C significantly decreased the concentration of nitric oxide (NO) and the activity of nitric oxide synthase (NOS) in hemolymph (P < 0.05). Diet with 133.94 mg/kg vitamin C was improved the activity of polyphenol oxidase (PPO) and the concentration of albumin (ALB) in hemolymph. Crabs fed diet with 133.94 mg/kg vitamin C showed lower concentration of malondialdehyde (MDA) in hemolymph and hepatopancreas than those fed the other diets. Meanwhile, crabs fed diet with 98.45 mg/kg vitamin C showed higher activity of total superoxide dismutase (T-SOD) in hemolymph, and crabs fed diet with 133.94 mg/kg vitamin C showed higher activity of T-SOD in hepatopancreas. Crabs fed diet with 186.36 mg/kg vitamin C significantly decreased the activities of reduced glutathione (GSH) and glutathione peroxidase (GSH-PX) in hepatopancreas (P < 0.05). In normal temperature, crabs fed diets with 133.94 mg/kg vitamin C significantly up-regulated the expression levels of gpx (glutathione peroxidase) and trx (thioredoxin) in hepatopancreas compared with the control treatment (P < 0.05). The highest expression levels of relish, il16 (interleukin 16), caspase 2 (caspase 2), p38 mapk (p38 mitogen-activated protein kinases) and bax (bcl-2 associated x protein) in hepatopancreas were found at crabs fed control diet (P < 0.05). Moreover, crabs fed diet with 133.94 mg/kg vitamin C showed higher expression levels of alf-3 (anti-lipopolysaccharide factor 3) and bcl-2 (B-cell lymphoma 2) in hepatopancreas than those fed the other diets (P < 0.05). Under low-temperature stress, crabs fed diet with 133.94 mg/kg vitamin C significantly improved the expression levels of hsp90 (heat shock protein 90), cat (catalase), gpx, prx (thioredoxin peroxidase) and trx in hepatopancreas (P < 0.05). In addition, dietary with 133.94 vitamin C significantly up-regulated the expression levels of alf-3 and bcl-2 (P < 0.05). Based on two slope broken-line regression analysis of activity of PPO against the dietary vitamin C level, the optimal dietary vitamin C requirement was estimated to be 144.81 mg/kg for juvenile mud crab. In conclusion, dietary 133.94 to 144.81 mg/kg vitamin C significantly improved the non-specific immune defense, antioxidant capacity and resistance to low-temperature stress of juvenile mud crab.

A blend of chitosan-vitamin C and vitamin E nanoparticles robust the immunosuppressed- status in Nile tilapia treated with salt

In aquaculture, fish are exposed to many stressors, such as climate changes and infectious diseases that affect their performance, immunity, and welfare. Freshwater fish subjected to salt bath become exhausted and stressed. In this experiment, Nile tilapia were exposed to a salt bath at a dose of 30 ppt for 30 min a day. Vitamin C and vitamin E are well-known antioxidants that are used in aquaculture. Fish received dietary nanoparticles of chitosan-vitamin C and chitosan-vitamin E (CCE-NPs) for different periods (7 and 14 days) pre- (G2) and post-salt treatment (G3). In the control fish (G1), cortisol 5.44 µg/dL and glucose 91.67 mg/dL were significantly up-regulated post-salt treatment by 1 h and 24 h, respectively, whereas those (G2) fed CCE-NPs diet had significantly lower values of 4.72 and 3.25 µg/dL; 86.3 and 84.3 mg/dL, respectively. A rapid decrease of glucose 68.3 and 66.3 mg/dL was noticed in those (G2) fed CCE-NPs diet compared to the control 84.67 mg/dL at 48 h post-stress. Regardless of the supplementation period, fish (G2) could partially restore normal food reflex at 48 h (post-salt bath) and fully restored at 72 h compared to 7 days in the control (G1). After 48 h, fish that received dietary CCE-NPs (G2 and G3) restored normal mucus lysozyme levels, whereas the control did not restore pre-treatment values till the seventh day. Mucus antibacterial activity, fish received rapid dietary CCE-NPs (G2) and partially restored average values (pre-salt bath) at 96 h. The salt treatment could provoke gene expression of pro-inflammatory cytokines interleukin (IL-1β) and tumor necrosis (TNF)-α in the head kidney of fish at 24 h post-salt bath to 5.9-8.35 fold-change, respectively, with a rapid decline in fish (G2) the gene expression. Post-salt bath (24 h), the gene expression of glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) was higher in fish (G2) than in the control group (G1) regardless of the supplementation period (7 and 14 days). Bacterial infection S. agalactiae (OL471408), a significantly lower MR was recorded in G2 at 40% and 33.3% compared to the control G1 MR (53.3%), with an RPL of 24.95% and 37.5%. In conclusion, Nile tilapia treated with a 30 ppt salt became more vulnerable to S. agalactiae. Adding CCE-NPs to the Nile tilapia diet for 7- and 14-day pre-salt bath could increase immune and antioxidant-related gene expression to counteract S. agalactiae infection.

Climate change can impair bacterial pathogen defences in sablefish via hypoxia-mediated effects on adaptive immunity

Low-oxygen levels (hypoxia) in aquatic habitats are becoming more common because of global warming and eutrophication. However, the effects on the health/disease status of fishes, the world's largest group of vertebrates, are unclear. Therefore, we assessed how long-term hypoxia affected the immune function of sablefish, an ecologically and economically important North Pacific species, including the response to a formalin-killed Aeromonas salmonicida bacterin. Sablefish were held at normoxia or hypoxia (100% or 40% air saturated seawater, respectively) for 6-16 weeks, while we measured a diverse array of immunological traits. Given that the sablefish is a non-model organism, this involved the development of a species-specific methodological toolbox comprised of qPCR primers for 16 key immune genes, assays for blood antibacterial defences, the assessment of blood immunoglobulin (IgM) levels with ELISA, and flow cytometry and confocal microscopy techniques. We show that innate immune parameters were typically elevated in response to the bacterial antigens, but were not substantially affected by hypoxia. In contrast, hypoxia completely prevented the ∼1.5-fold increase in blood IgM level that was observed under normoxic conditions following bacterin exposure, implying a serious impairment of adaptive immunity. Since the sablefish is naturally hypoxia tolerant, our results demonstrate that climate change-related deoxygenation may be a serious threat to the immune competency of fishes.

Nanobubble applications in aquaculture industry for improving harvest yield, wastewater treatment, and disease control

The ever-growing demand for aquaculture has led the industry to seek novel approaches for more sustainable practices. These attempts aim to increase aquaculture yield by increasing energy efficiency and decreasing footprint and chemical demand without compromising animal health. For this, emerging nanobubbles (NBs) aeration technology gained attention. NBs are gas-filled pockets suspended as sphere-like cavities (bulk NBs) or attached to surfaces (surface NBs) with diameters of <1 μm. Compared to macro and microbubbles, NBs have demonstrated unique characteristics such as long residence times in water, higher gas mass transfer efficiency, and hydroxyl radical production. This paper focuses on reviewing NB technology in aquaculture systems by summarizing and discussing uses and implications. Three focus areas were targeted to review the applicability and effects of NBs in aquaculture: (i) NBs aeration to improve the aquaculture harvest yield and subsequent wastewater treatment; (ii) NB application for inactivation of harmful microorganisms; and (iii) NBs for reducing oxidative stress and improving animal health. Thus, this study reviews the research studies published in the last 10 years in which air, oxygen, ozone, and hydrogen NBs were tested to improve gas mass transfer, wastewater treatment, and control of pathogenic microorganisms. The experimental results indicated that air and oxygen NBs yield significantly higher productivity, growth rate, total harvest, survival rate, and less oxygen consumption in fish and shrimp farming. Secondly, the application of air and ozone NBs demonstrated the ability of efficient pollutant degradation. Third, NB application demonstrated effective control of infectious bacteria and viruses, and thus increased fish survival, as well as different gene expression patterns that induce immune responses to infections. Reviewed studies lack robust comparative analyses of the efficacy of macro- and microbubble treatments. Also, potential health and safety implications, as well as economic feasibility through factors such as changes in capital infrastructure, routine maintenance and energy consumption need to be considered and evaluated in parallel to applicability. Therefore, even with a promising future, further studies are needed to confirm the benefits of NB treatment versus conventional aquaculture practices.

Gyrodactylus in the spotlight: how exposure to light impacts disease and the feeding behavior of the freshwater tropical guppy (Poecilia reticulata)

Artificial light at night (ALAN) negatively impacts organisms in many ways, from their feeding behaviors to their response and ability to deal with disease. Our knowledge of ALAN is focused on hosts, but we must also consider their parasites, which constitute half of all described animal species. Here, we assessed the impact of light exposure on a model host-parasite system (Poecilia reticulata and the ectoparasitic monogenean Gyrodactylus turnbulli). First, parasite-free fish were exposed to 12:12 h light:dark (control) or 24:0 h light:dark (ALAN) for 21 days followed by experimental infection. Second, naturally acquired G. turnbulli infections were monitored for 28 days during exposure of their hosts to a specified light regime (6:18 h, 12:12 h, or 24:0 h light:dark). Experimentally infected fish exposed to constant light had, on average, a greater maximum parasite burden than controls, but no other measured parasite metrics were impacted. Host feeding behavior was also significantly affected: fish under ALAN fed faster and took more bites than controls, whilst fish exposed to reduced light fed slower. Thus, ALAN can impact parasite burdens, even in the short term, and altering light conditions will impact fish feeding behavior. Such responses could initiate disease outbreaks or perturb food-webs with wider ecological impacts.

Hematological, biochemical and oxidative responses induced by thermal shock in juvenile Tambaqui (Colossoma macropomum) and its hybrid Tambatinga (Colossoma macropomum x Piaractus brachypomus)

The effects of thermal shock on hematological, biochemical and antioxidant responses were evaluated in liver tissue of juvenile tambaqui (Colossoma macropomum) and tambatinga (♀ C. macropomum × ♂ Piaractus brachypomus). Forty juveniles of tambaqui and 40 juveniles of tambatinga, of the same age and with an initial weight of 23.3 ± 6.7 g, were randomly distributed in eight 28L circular tanks. A tank (n = 10 fish) of tambaqui and a tank (n = 10 fish) of tambatinga were then used to obtain basal data. The other animals were subjected to thermal shock with sudden temperature reduction from 28 to 18 ºC. Blood and tissue were then collected after 1, 6 and 24 h from the onset of thermal shock. No mortality was observed during the experimental period. Thermal shock increased triglyceride levels after 24 h of stress for tambaqui and reduced values for tambatinga. There was an effect on plasma glucose only for fish group (P < 0.0001) and collection time (P < 0.0001) with a peak observed for the hybrid after 6 h. The interaction of factors for SOD indicated greater activity for tambatinga at the 6 h collection and lower at basal and 1 h collections. There was an interaction for CAT (P = 0.0020) with less activity for tambatinga at 1 h. However, thermal shock and hybridization did not influence GST and TBARS levels in liver tissue. Therefore, the results suggest that the hybrid, tambatinga, is more efficient at promoting adjustments of biochemical responses and antioxidant enzymes during thermal shock.

Gut physiology of rainbow trout (Oncorhynchus mykiss) is influenced more by short-term fasting followed by refeeding than by feeding fishmeal-free diets

Supplementing a fishmeal-free diet with yeast extract improves rainbow trout (Oncorhynchus mykiss) growth performance and modulates the hepatic and intestinal transcriptomic response. These effects are often observed in the long term but are not well documented after short periods of fasting. Fasting for a few days is a common practice in fish farming, especially before handling the fish, such as for short sorting, tank transfers, and vaccinations. In the present study, rainbow trout were subjected to a 4-day fast and then refed, for 8 days, a conventional diet containing fishmeal (control diet) or alternative diets composed of terrestrial animal by-products supplemented or not with a yeast extract. During the refeeding period alone, most of the parameters considered did not differ significantly in response to the different feeds. Only the expression of claudin-15 was upregulated in fish fed the yeast-supplemented diet compared to the control diet. Conversely, fasting followed by refeeding significantly influenced most of the parameters analyzed. In the proximal intestine, the surface area of villi significantly increased, and the density of goblet cell tended to decrease during refeeding. Although no distinct plasma immune response or major signs of gut inflammation were observed, some genes involved in the structure, complement pathway, antiviral functions, coagulation, and endoplasmic reticulum stress response of the liver and intestine were significantly regulated by refeeding after fasting. These results indicate that short-term fasting, as commonly practiced in fish farming, significantly alters the physiology of the liver and intestine regardless of the composition of the diet.

Molecular, behavioral, and growth responses of juvenile yellow catfish (Tachysurus fulvidraco) exposed to carbamazepine

Carbamazepine (CBZ) is an anticonvulsant medication used to treat epilepsy and bipolar disorder. Due to its persistence and low removal rate in wastewater treatment plants, it is frequently detected in the environment, raising concerns regarding its potential adverse effects on aquatic organisms and ecosystems. In this study, we aimed to assess the impact of CBZ on the behavior and growth of juvenile yellow catfish Tachysurus fulvidraco, a native and economically important species in China. Fish were exposed to CBZ at three concentrations of 1, 10, or 100 µg/L for 14 days. The fish exposed to 10 and 100 μg/L of CBZ exhibited decreased feeding, and a significant increase in cannibalistic tendencies was observed in fish exposed to 100 μg/L CBZ. Acetylcholinesterase activity was increased in the brain of fish exposed to 100 μg/L CBZ. CBZ also inhibited the growth of yellow catfish. To better elucidate mechanisms of toxicity, transcriptomics was conducted in both the brain and liver. In the brain, gene networks associated with neurotransmitter dysfunction were altered by CBZ, as well as networks associated with mitochondrial dysfunction and metabolism. In the liver, gene networks associated with the immune system were altered by CBZ. The current study improves comprehension of the sub-lethal effects of CBZ and reveals novel insight into molecular and biochemical pathways disrupted by CBZ, identifying putative key events associated with reduced growth and altered behavior. This study emphasizes the necessity for improved comprehension of the effects of pharmaceutical contaminants on fish at environmentally relevant levels.

How does temperature rise affect a freshwater catfish Rhamdia quelen? A proteomic approach

Outside of scientific circles, climate change is a hotly debated topic due to all its consequences. Changes in the temperature can affect aquatic organisms and it is important to understand and to detect earlier signals. This study aimed to analyze how a Neotropical fish species responds to temperature increases, using proteomic analysis as a tool. For this, fish of the species Rhamdia quelen, male and female, were exposed to two temperatures: 25 °C and 30 °C. After 96 h, the animals were anesthetized, euthanized and the liver was collected for proteomic analysis. Using freely available online software and databases (e.g. MetaboAnalyst, Gene Ontology and UniProt), we define the altered proteins in both sexes: 42 in females and 62 in males. Data are available via ProteomeXchange with identifier PXD046475. Differences between the two temperatures were observed mainly in the amino acid metabolic pathways. The cellular process and the immune response was altered, indicating that effects at lower levels of biological organization could serve as a predictor of higher-level effects when temperature rise affects wildlife populations. Thus, we conclude that the increase in temperature is capable of altering important cellular and physiological processes in R. quelen fish, with this response being different for males and females.

Effects of Chronic Heat Stress on Growth, Apoptosis, Antioxidant Enzymes, Transcriptomic Profiles, and Immune-Related Genes of Hong Kong Catfish (Clarias fuscus)

Chronic heat stress can have detrimental effects on the survival of fish. This study aimed to investigate the impact of prolonged high temperatures on the growth, antioxidant capacity, apoptosis, and transcriptome analysis of Hong Kong catfish (Clarias fuscus). By analyzing the morphological statistics of C. fuscus subjected to chronic high-temperature stress for 30, 60, and 90 days, it was observed that the growth of C. fuscus was inhibited compared to the control group. The experimental group showed a significant decrease in body weight and body length compared to the control group after 60 and 90 days of high-temperature stress (p < 0.05, p < 0.01). A biochemical analysis revealed significant alterations in the activities of three antioxidant enzymes superoxide dismutase activity (SOD); catalase activity (CAT); glutathione peroxidase activity (GPx), the malondialdehyde content (MDA), and the concentrations of serum alkaline phosphatase (ALP); Aspartate aminotransferase (AST); and alanine transaminase (ALT) in the liver. TUNEL staining indicated stronger apoptotic signals in the high-temperature-stress group compared to the control group, suggesting that chronic high-temperature-induced oxidative stress, leading to liver tissue injury and apoptosis. Transcriptome analysis identified a total of 1330 DEGs, with 835 genes being upregulated and 495 genes being downregulated compared to the control group. These genes may be associated with oxidative stress, apoptosis, and immune response. The findings elucidate the growth changes in C. fuscus under chronic high temperature and provide insights into the underlying response mechanisms to a high-temperature environment.

The P4' Peptide-Carrying Bacillus subtilis in Cottonseed Meal Improves the Chinese Mitten Crab Eriocheir sinensis Innate Immunity, Redox Defense, and Growth Performance

This study developed a recombinant Bacillus subtilis to carry the LGSPDVIVIR peptide (cmP4) isolated from the hydrolyzed products of cottonseed meal with excellent antioxidant and immune-enhancing properties in vitro. It was carried as a tandem of five cmP4 peptides (cmP4') to be stably expressed on a large scale. Then, its effectiveness was evaluated in Chinese mitten crab (Eriocheir sinensis) based on growth performance, redox defense, and innate immunity. A total of 280 crabs (mean body weight: 41.40 ± 0.14) were randomly assigned to seven diets including a control one (without B. subtilis) and six experimental ones with different doses (107,108, and 109 CFU/kg) of unmodified and recombinant B. subtilis, respectively, for 12 weeks. Each diet was tested in four tanks of crabs (10/tank). In terms of bacterial dosages, the final weight (FW), weight gain (WG), hemolymph and hepatopancreatic activities of superoxide dismutase (SOD), catalase (CAT), lysosome (LZM), acid phosphatase (ACP) and alkaline phosphatase (AKP), and hepatopancreatic transcriptions of cat, mitochondrial manganese superoxide dismutase (mtmnsod), thioredoxin-1 (trx1), and prophenoloxidase (propo) all increased significantly with increasing B. subtilis dosages, while hemolymph and hepatopancreatic malondialdehyde (MDA) content and the transcriptions of toll like receptors (tlrs), NF-κB-like transcription factor (relish), and lipopolysaccharide-induced TNF-α factor (litaf) all decreased remarkably. In terms of bacterial species, the recombinant B. subtilis group obtained significantly high values of FW, WG, hemolymph, and hepatopancreatic activities of SOD, CAT, LZM, ACP, and AKP, and the transcriptions of mtmnsod, peroxiredoxin 6 (prx6), and propo compared with the unmodified B. subtilis, while opposite results were noted in hemolymph and hepatopancreatic MDA content and the transcriptions of tlrs, relish, and litaf. These results indicated that dietary supplementation with 109 CFU/kg of recombinant B. subtilis can improve the growth performance, redox defense, and nonspecific immunity of E. sinensis.

Evaluation of Post-Surgical Recovery in Olive Flounder (Paralichthys olivaceus) by Assessing Behavior, Heart Rate, and Wound Healing

This study examined the post-surgery recovery of olive flounder (Paralichthys olivaceus) following tag insertion by analyzing behavior, heart rate, and wound healing. The experiments used 30 individuals (length: 38.67 ± 2.12 cm; weight: 742.48 ± 116.41 g). Heart rate was measured using a DST milli-HRT (Star-Oddi) bio-logger. To assess the influence of water temperature on the recovery process after surgical tag insertion, behavioral analyses, heart rate, and wound healing were conducted in two experimental groups: Experiment 1 (22 °C, optimal water temperature); Experiment 2 (28 °C, high water temperature); and control group (22 °C, non-operated fish). The experiment was repeated twice over a 7-day period for each experimental group. Compared to the non-operated fish, the operated fish exhibited stable levels after the 3rd to 4th day in Experiment 1. Statistical analyses based on heart rate in Experiment 1 indicated that the appropriate post-surgery recovery time point was approximately 3 days, representing the point at which behavioral fluctuations stabilized. In the case of Experiment 2, abnormal behavioral patterns (e.g., tilted swimming) and changes in average swimming time and daily heart rate were found to stabilize after 4 days post-surgery.

Gut-immunity modulation in Lepidocephalichthys guntea during Aeromonas hydrophila-infection and recovery assessed with transcriptome data

The fish immune system, which consists of innate and adaptive immunologic processes, defends against viruses, bacteria, fungi, and parasites. The gut immunity is an integral part of the host immune system that controls immunological homeostasis, hosts' interactions with their microbiomes, and provides defence against a number of intestinal infections. Lepidocephalichthys guntea, a facultative air-breathing fish, was experimentally infected with Aeromonas hydrophila using intraperitoneal injection followed by bath challenge, and transcriptome data were used to examine the gut immune responses during disease progression and recovery from the diseased state without the use of medication. For the control or uninfected fish (FGC) and the infected fish that were kept for seven days (FGE1) and fifteen days (FGE2), separate water tanks were set up. Coding DNA sequences (CDS) for FGC and FGE1, FGC and FGE2, and FGE1 and FGE2 were analyzed for differential gene expression (DGE). The presence and expression of genes involved in the T cell receptor (TCR) signalling pathway, natural killer (NK) cell-mediated cytotoxicity pathway, and complement-mediated pathway, along with a large number of other immune-related proteins, and heat shock protein (HSPs) under various experimental conditions and its relationship to immune modulation of the fish gut was the primary focus of this study. Significant up-and-down regulation of these pathways shows that, in FGE1, the fish's innate immune system was engaged, whereas in FGE2, the majority of innate immune mechanisms were repressed, and adaptive immunity was activated. Expression of genes related to the immune system and heat-shock proteins was induced during this host's immunological response, and this information was then used to build a thorough network relating to immunity and the heat-shock response. This is the first study to examine the relationship between pathogenic bacterial infection, disease reversal, and modification of innate and adaptive immunity as well as heat shock response.

Host-microbiota-parasite interactions in two wild sparid fish species, Diplodus annularis and Oblada melanura (Teleostei, Sparidae) over a year: a pilot study

BACKGROUND

The microbiota in fish external mucus is mainly known for having a role in homeostasis and protection against pathogens, but recent evidence suggests it is also involved in the host-specificity of some ectoparasites. In this study, we investigated the influence of seasonality and environmental factors on both fish external microbiota and monogenean gill ectoparasites abundance and diversity and assessed the level of covariations between monogenean and bacterial communities across seasons. To do so, we assessed skin and gill microbiota of two sparid species, Oblada melanura and Diplodus annularis, over a year and collected their specific monogenean ectoparasites belonging to the Lamellodiscus genus.

RESULTS

Our results revealed that diversity and structure of skin and gill mucus microbiota were strongly affected by seasonality, mainly by the variations of temperature, with specific fish-associated bacterial taxa for each season. The diversity and abundance of parasites were also influenced by seasonality, with the abundance of some Lamellodiscus species significantly correlated to temperature. Numerous positive and negative correlations between the abundance of given bacterial genera and Lamellodiscus species were observed throughout the year, suggesting their differential interaction across seasons.

CONCLUSIONS

The present study is one of the first to demonstrate the influence of seasonality and related abiotic factors on fish external microbiota over a year. We further identified potential interactions between gill microbiota and parasite occurrence in wild fish populations, improving current knowledge and understanding of the establishment of host-specificity.

Integrated metabolomic and transcriptomic responses to heat stress in a high-altitude fish, Triplophysa siluroides

Species in Triplophysa display strong adaptability to the extreme environment of the plateau, thus offering an ideal model to study the molecular mechanism of fish adaptation to environmental stress. In the present study, we conducted integrated analysis of the transcriptome and metabolism of liver tissue in Triplophysa siluroides under heat stress (28 °C) and control (10 °C) conditions to identify heat stress-induced genes, metabolites and pathways. RNA-Seq identified 2373 differentially expressed genes, which consisted of 1360 upregulated genes and 1013 downregulated genes, in the heat stress group vs. the control group. Genes in the heat shock protein (Hsp) family, including Hsp40, Hsp70, Hsp90 and other Hsps, were strongly upregulated by heat stress. Pathway enrichment analysis revealed that the PI3K/AKT/mTOR and protein processing in the endoplasmic reticulum (ER) pathways were significantly affected by heat stress. Metabolism sequencing identified a total of 155 differentially abundant metabolites, including 118 significantly upregulated metabolites and 37 downregulated metabolites. Combined analysis of the transcriptome and metabolism results showed that ubiquitin-dependent proteolysis and purine metabolism pathways were enhanced in response to acute heat stress to protect cells from damage under stress conditions. The results of this study may contribute to our understanding of the underlying molecular mechanism of the heat stress response in cold-water fish.

Potential role of miR-8159-x in heat stress response in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) is a representative species of cold-water fish. Elevated temperatures during summer often result in significant high mortality rates. MicroRNAs (miRNAs) are class of small non-coding RNAs that play a crucial role as post-transcriptional regulators in various biological processes. Emerging evidence suggests that miRNAs are important regulators role during heat stress. Analyzing previously obtained miRNA-sequencing data, we observed substantial down regulation of miR-8159-x in the liver tissue of heat stressed rainbow trout. In this study, we conducted a dual luciferase reporter assay to validate that miR-8159-x target, a key gene involved in heat stress in rainbow trout. By examining the expression patterns of miR-8159-x and hsp90a1 in the liver tissue at 18 °C (CG) and 24 °C (HS) groups, we propose that miR-8159-x may negatively regulate hsp90a1. Furthermore, in vitro hepatocyte assay, transfection with miR-8159-x mimics significantly reduced the expression level of hsp90a1, whereas transfection with a miR-8159-x inhibitor yielded the opposite effect. Additionally, overexpression of miR-8159-x inhibited cell proliferation and induced apoptosis in normal rainbow trout hepatocytes. We further investigated the effects of miR-8159-x overexpression or inhibition on the mRNA and protein levels of the target gene hsp90a1 under heat stress conditions. In conclusion, our findings suggest that miR-8159-x participates in the biological response to heat stress by targeting hsp90a1. These results contribute to a better understanding of the molecular mechanisms underlying heat stress in rainbow trout and provide valuable insights for future research.

Effects of acute heat stress on haemato-biochemical parameters, oxidative resistance ability, and immune responses of hybrid yellow catfish (pelteobagrus fulvidraco × P. vachelli) juveniles

This study investigated the effect of heat stress on the physiological parameters, oxidation resistance ability and immune responses in juvenile hybrid yellow catfish. Heat stress group exposed to 35 °C and control to 28 °C. Blood and liver were sampled at different hours' post-exposure. Results showed that red blood cell (RBC), white blood cell (WBC) counts, Hemoglobin (HGB) levels and hematocrit (HCT) values increased significantly (P < 0.05) post-exposure to heat stress. This indicates the increase of cell metabolism. Serum alanine aminotransferase (ALT) and aspartate transaminase (AST) activities, total cholesterol (TC), total protein (TP), triglyceride (TG) and glucose increased significantly (P < 0.05) indicating the need to cope with stress and cell damage. Liver TC, TG, COR hormone, C3 complement increased significantly from 24 to 96 h. Heat stress mostly affects the hepatic antioxidant and immune resistance functions, resulting in increments of cortisol levels, lysozyme, superoxide dismutase (SOD), and catalase (CAT) enzyme activities. The increase of Malondialdehyde (MDA), alkaline phosphatase (AKP) indicate stimulation of the immune responses to protect the liver cells from damage. The decrease in Liver TP indicated liver impairment. Decrease in Glycogen content from 6 to 96 h indicated mobilization of more metabolites to cope with increased energy demand. Interestingly, results showed that heat stress trigged costly responses in the experimental fish like accelerated metabolism and deplete energy reserves, which could indirectly affect ability of fish to set up efficient long term defense responses against stress. These results provide insight into prevention and management of stress in juvenile hybrid yellow catfish.

LC-MS/MS based characterisation and differential expression of proteins in Himalayan snow trout, Schizothorax labiatus using LFQ technique

Molecular characterization of fish muscle proteins are nowadays considered as a key component to understand the role of specific proteins involved in various physiological and metabolic processes including their up and down regulation in the organisms. Coldwater fish specimens including snow trouts hold different types of proteins which help them to survive in highly diversified temperatures fluctuating from 0 to 20 °C. So, in current study, the liquid chromatography mass spectrometry using label free quantification technique has been used to investigate the muscle proteome profile of Schizothorax labiatus. For proteomic study, two weight groups of S. labiatus were taken from river Sindh. The proteomic analysis of group 1 revealed that a total of 235 proteins in male and 238 in female fish were recorded. However, when male and female S. labiatus were compared with each other on the basis of spectral count and abundance of peptides by ProteinLynx Global Server software, a total of 14 down-regulated and 22 up-regulated proteins were noted in this group. The highly down-regulated ones included homeodomain protein HoxA2b, retinol-binding protein 4, MHC class II beta chain and proopiomelanocortin while as the highly expressed up-regulated proteins comprised of gonadotropin I beta subunit, NADH dehydrogenase subunit 4, manganese superoxide dismutase, recombinase-activating protein 2, glycosyltransferase, chymotrypsin and cytochrome b. On the other hand, the proteomic characterisation of group 2 of S. labiatus revealed that a total of 227 proteins in male and 194 in female fish were recorded. When male and female S. labiatus were compared with each other by label free quantification, a total of 20 down-regulated and 18 up-regulated proteins were recorded. The down-regulated protein expression of group 2 comprised hepatic lipase, allograft inflammatory factor-1, NADH dehydrogenase subunit 4 and myostatin 1 while the highly expressed up-regulated proteins included glycogen synthase kinase-3 beta variant 2, glycogen synthase kinase-3 beta variant 5, cholecystokinin, glycogen synthase kinase-3 beta variant 3 and cytochrome b. Significant (P < 0.05) difference in the expression of down-regulated and up-regulated proteins was also noted between the two sexes of S. labiatus in each group. According to MS analysis, the proteins primarily concerned with the growth, skeletal muscle development and metabolism were down-regulated in river Sindh, which indicates that growth of fish during the season of collection i.e., winter was slow owing to less food availability, gonad development and low metabolic activity. While, the proteins related to immune response of fish were also noted to be down-regulated thereby signifying that the ecosystem has less pollution loads, microbial, pathogenic and anthropogenic activities. It was also found that the proteins involved in glycogen metabolism, reproductive and metabolic processes, particularly lipid metabolism were up-regulated in S. labiatus. The significant expression of these proteins may be connected to pre-spawning, gonad development and use of stored food as source of energy. The information generated in this study can be applied to future research aimed at enhancing food traceability, food safety, risk management and authenticity analysis.

Effect of Copper Sulphate Exposure on the Oxidative Stress, Gill Transcriptome and External Microbiota of Yellow Catfish, Pelteobagrus fulvidraco

This study aimed to investigate the potential adverse effects of the practical application of copper sulfate on yellow catfish (Pelteobagrus fulvidraco) and to provide insights into the gill toxicity induced by copper sulphate. Yellow catfish were exposed to a conventional anthelmintic concentration of copper sulphate (0.7 mg/L) for seven days. Oxidative stress biomarkers, transcriptome, and external microbiota of gills were examined using enzymatic assays, RNA-sequencing, and 16S rDNA analysis, respectively. Copper sulphate exposure led to oxidative stress and immunosuppression in the gills, with increased levels of oxidative stress biomarkers and altered expression of immune-related differentially expressed genes (DEGs), such as IL-1β, IL4Rα, and CCL24. Key pathways involved in the response included cytokine-cytokine receptor interaction, NOD-like receptor signaling pathway, and Toll-like receptor signaling pathway. The 16S rDNA analysis revealed copper sulphate altered the diversity and composition of gill microbiota, as evidenced by a significant decrease in the abundance of Bacteroidotas and Bdellovibrionota and a significant increase in the abundance of Proteobacteria. Notably, a substantial 8.5-fold increase in the abundance of Plesiomonas was also observed at the genus level. Our findings demonstrated that copper sulphate induced oxidative stress, immunosuppression, and gill microflora dysbiosis in yellow catfish. These findings highlight the need for sustainable management practices and alternative therapeutic strategies in the aquaculture industry to mitigate the adverse effects of copper sulphate on fish and other aquatic organisms.

The role of the microbiome on fish mucosal immunity under changing environments

The environment is crucial for fish as their mucosal surfaces face continuous challenges in the water. Fish mucosal surfaces harbor the microbiome and mucosal immunity. Changes in the environment could affect the microbiome, thus altering mucosal immunity. Homeostasis between the microbiome and mucosal immunity is crucial for the overall health of fish. To date, very few studies have investigated mucosal immunity and its interaction with the microbiome in response to environmental changes. Based on the existing studies, we can infer that environmental factors can modulate the microbiome and mucosal immunity. However, we need to retrospectively examine the existing literature to investigate the possible interaction between the microbiome and mucosal immunity under specific environmental conditions. In this review, we summarize the existing literature on the effects of environmental changes on the fish microbiome and mucosal immunity. This review mainly focuses on temperature, salinity, dissolved oxygen, pH, and photoperiod. We also point out a gap in the literature and provide directions to go further in this research field. In-depth knowledge about mucosal immunity-microbiome interaction will also improve aquaculture practices by reducing loss during environmental stressful conditions.

Influence of Seasonality and Culture Stage of Farmed Nile Tilapia (Oreochromis niloticus) with Monogenean Parasitic Infection

The aim of this study was to observe how abiotic and biotic factors in a tropical region influence the rate of monogenean parasitism in Nile tilapia (Oreochromis niloticus) that are farmed in net cages. A total of 240 sexually reversed fish were analyzed, and 20 from each culture stage were collected during each sampling month. Overall, 60 fish were sampled in April (autumn), 60 in August (winter), 60 in November (spring), and 60 in February (summer). Fish were collected from a commercial fish farm located in Capivara Reservoir in the lower Paranapanema River region of Paraná, Brazil. In total, 3290 monogenean parasites were collected from fish gills of the following species: Cichlidogyrushalli, C. thurstonae, Scutogyruslongicornis, C. cirratus, C. sclerosus, and C. tilapiae. Higher parasitological indices were observed in colder seasons with lower precipitation. Autumn had the highest parasitic infection values compared to the other seasons. The occurrence of monogenean parasites showed a negative correlation with season, in contrast to the culture stage, in which there was a positive correlation. These results may provide a means for establishing adequate fish farm management to predict periods of high monogenean infestation.

Effects of artificial photoperiods on antigen-dependent immune responses in rainbow trout (Oncorhynchus mykiss)

In this study, we investigated the effects of the artificial photoperiods that mimic summer (16L:8D) and winter (8L:16D) solstices, equinoxes (12L:12D), and the artificial 24-h light regimen (24L:0D) on the leukocyte populations and the T helper and regulatory type responses on rainbow trout (Oncorhynchus mykiss). Using flow cytometry analysis, we found that photoperiod induces changes in head kidney leukocyte subsets. The lymphoid subset increased in the 16L:8D summer solstice regime. The analysis using antibodies against B and T cells showed the increase of CD4-1⁺ T lymphocytes and other unidentified lymphoid cells, with no changes in the B cells. To investigate the modulatory influence of the photoperiod on the fish T cell response, we quantified in the head kidney the transcript levels of genes involved in the Th1 type response (t-bet, ifn-ƴ, il-12p35, il-12p40c), Th2 type response (gata3, il-4/13a), Th17 response (ror-ƴt, il-17a/f), T regulatory response (foxp3α, il-10a, tgf-β1), and the T cell growth factor il-2. The results showed that the seasonal photoperiod alone has a limited influence on the expression of these genes, as the only difference was observed in il-14/13a and il-10a transcripts of fish kept on the 16L:8D regimen. In addition, the 24L:0D treatment used in aquaculture produces a reduction of il-14/13a and il-17a/f. We also evaluated the effect of photoperiod in the presence of an antigenic stimulus. Thus, in fish immunized with the recombinant viral protein 1 (rVP1) of infectious pancreatic necrosis virus (IPNV), the photoperiod had a striking influence on the type of adaptive immune response. Each photoperiod fosters a unique immune signature of antigenic response. A classical type 1 response is observed in fish subjected to the 16D:8L photoperiod. In contrast, fish in the 12L:12D photoperiod showed only the upregulation of il-12p40c. Furthermore, none of the cytokines were increased in fish maintained on the artificial 24L:0D regimen, and a decrease in the master transcription factors (t-bet, ror-ƴt, and foxp3α) was observed. Thus, fish on the 12L:12D and 24L:0D photoperiod appear hyporesponsive regarding the T cell response. Altogether, this study showed that photoperiods modify the magnitude and quality of the T-helper response in rainbow trout and thus impact essential mechanisms for the generation of immune memory and protection against microorganisms.

Withania coagulans fruit extract: a possible useful additive in ameliorating growth and immunity of Labeo rohita (Hamilton, 1822)

This study aimed to assess the Withania coagulans fruit extract's effects on growth and haematological parameters of Labeo rohita. Healthy fish (n = 120) were divided in four groups. Experimental diet was prepared with different extraction of W. coagulans (0%, 1%, 1.5% and 2%). Diet was provided for eight weeks to all groups except the control group which fed on basal diet. The 1.5% and 2% W. coagulans extracts lead improvement in feed conversion ratio and specific fish growth rate; haematological parameters in fish group fed with 2% of W. coagulans showed increased in WBC, RBC, Hb, MCHC, PCV. The values of plasma proteins and lysozyme activity were higher in the experimental group compared control group. Fish fed with W. coagulans extracts showed increased of immunity and less mortality respect to others. It suggested that W. coagulans could be considered valuable support for the improve growth and immunity in Labeo rohita.

Decreased water temperature enhance Piscine orthoreovirus genotype 3 replication and severe heart pathology in experimentally infected rainbow trout

Piscine orthoreovirus genotype 3 (PRV-3) was first discovered in Denmark in 2017 in relation to disease outbreaks in rainbow trout (Oncorhynchus mykiss). While the virus appears to be widespread in farmed rainbow trout, disease outbreaks associated with detection of PRV-3 have only occurred in recirculating aquaculture systems, and has predominantly been observed during the winter months. To explore the possible effects of water temperature on PRV-3 infection in rainbow trout, an in vivo cohabitation trial was conducted at 5, 12, and 18°C. For each water temperature, a control tank containing mock-injected shedder fish and a tank with PRV-3 exposed fish were included. Samples were collected from all experimental groups every 2nd week post challenge (WPC) up until trial termination at 12 WPC. PRV-3 RNA load measured in heart tissue of cohabitants peaked at 6 WPC for animals maintained at 12 and 18°C, while it reached its peak at 12 WPC in fish maintained at 5°C. In addition to the time shift, significantly more virus was detected at the peak in fish maintained at 5°C compared to 12 and 18°C. In shedders, fish at 12 and 18°C cleared the infection considerably faster than the fish at 5°C: while shedders at 18 and 12°C had cleared most of the virus at 4 and 6 WPC, respectively, high virus load persisted in the shedders at 5°C until 12 WPC. Furthermore, a significant reduction in the hematocrit levels was observed in the cohabitants at 12°C in correlation with the peak in viremia at 6 WPC; no changes in hematocrit was observed at 18°C, while a non-significant reduction (due to large individual variation) trend was observed at cohabitants held at 5°C. Importantly, isg15 expression was positively correlated with PRV-3 virus load in all PRV-3 exposed groups. Immune gene expression analysis showed a distinct gene profile in PRV-3 exposed fish maintained at 5°C compared to 12 and 18°C. The immune markers mostly differentially expressed in the group at 5°C were important antiviral genes including rigi, ifit5 and rsad2 (viperin). In conclusion, these data show that low water temperature allow for significantly higher PRV-3 replication in rainbow trout, and a tendency for more severe heart pathology development in PRV-3 injected fish. Increased viral replication was mirrored by increased expression of important antiviral genes. Despite no mortality being observed in the experimental trial, the data comply with field observations of clinical disease outbreaks during winter and cold months.

Transcriptome analysis reveals the high temperature induced damage is a significant factor affecting the osmotic function of gill tissue in Siberian sturgeon (Acipenser baerii)

BACKGROUND

Maintaining osmotic equilibrium plays an important role in the survival of cold-water fishes. Heat stress has been proven to reduce the activity of Na⁺/K⁺-ATPase in the gill tissue, leading to destruction of the osmotic equilibrium. However, the mechanism of megatemperature affecting gill osmoregulation has not been fully elucidated.

RESULTS

In this study, Siberian sturgeon (Acipenser baerii) was used to analyze histopathological change, plasma ion level, and transcriptome of gill tissue subjected to 20℃, 24℃and 28℃. The results showed that ROS level and damage were increased in gill tissue with the increasing of heat stress temperature. Plasma Cl^- level at 28℃ was distinctly lower than that at 20℃ and 24℃, while no significant difference was found in Na⁺ and K⁺ ion levels among different groups. Transcriptome analysis displayed that osmoregulation-, DNA-repair- and apoptosis-related terms or pathways were enriched in GO and KEGG analysis. Moreover, 194 osmoregulation-related genes were identified. Amongst, the expression of genes limiting ion outflow, occluding (OCLN), and ion absorption, solute carrier family 4, member 2 (AE2) solute carrier family 9, member 3 (NHE3) chloride channel 2 (CLC-2) were increased, while Na⁺/K⁺-ATPase alpha (NKA-a) expression was decreased after heat stress.

CONCLUSIONS

This study reveals for the first time that the effect of heat stress on damage and osmotic regulation in gill tissue of cold-water fishes. Heat stress increases the permeability of fish's gill tissue, and induces the gill tissue to keep ion balance through active ion absorption and passive ion outflow. Our study will contribute to research of global-warming-caused effects on cold-water fishes.

Freshwater transfer affected intestinal microbiota with correlation to cytokine gene expression in Asian sea bass

As a catadromous fish, Asian sea bass (Lates calcarifer) juveniles migrate from seawater (SW) to freshwater (FW) for growth and development. During migration, they undergo physiological changes to acclimate to environmental salinity. Thus, it is crucial to understand how SW-to-FW migration affects the gut microbiota of catadromous fish. To the best of our knowledge, no study has revealed the effects of transfer to hypotonic environments on a catadromous fish microbiota. In this study, we aimed to determine the effects of FW transfer on the microbiota and cytokine gene expression in the intestines of juvenile catadromous Asian sea bass. The relationship between the water and the gut microbiota of this euryhaline species was also examined. We found that FW transfer affected both mucosa- and digesta-associated microbiota of Asian sea bass. Plesiomonas and Cetobacterium were dominant in both the mucosa- and digesta-associated microbiota of FW-acclimated sea bass. The pathogenic genera Vibrio, Staphylococcus, and Acinetobacter were dominant in the SW group. Although dominant fish microbes were present in the water, fish had their own unique microbes. Vitamin B6 metabolism was highly expressed in the FW fish microbiota, whereas arginine, proline, and lipid metabolism were highly expressed in the SW fish microbiota. Additionally, the correlation between cytokine gene expression and microbiota was found to be affected by FW transfer. Taken together, our results demonstrated that FW transfer altered the composition and functions of mucosa- and digesta-associated microbiota of catadromous Asian sea bass intestines, which correlated with cytokine gene expression.

Temperature dependent cellular, and epigenetic regulatory mechanisms underlying the antiviral immunity in sevenband grouper to nervous necrosis virus infection

Changes in the thermal optima of fish impacts changes in the physiology and immune response associated with infections. The present study showed that at suboptimal temperatures (17 °C), the host tries to evade viral infection by downregulating the inflammatory response through enhanced neuronal protection. There was significantly less abundance of IgM + B cells in the 17 °C group compared to that in the 25 °C group. An increased macrophage population (Iba1+) during the survival phase in fish challenged at 25 °C demonstrated inflammation. Optimal temperature challenge activated virus-induced senescence in brain cells, demonstrated with a heterochromatin-associated H3K9me3 histone mark. There was an abundant expression of anti-inflammatory cytokines in the brain of fish at the suboptimal challenge. Besides the cytokines, the expression of BDNF was significantly higher in the suboptimally challenged group, suggesting that its neuronal protection activity following NNV infection is mediated through TGFβ. The suboptimal challenge resulted in H3k9ac displaying transcriptional competency, activation of trained immunity H3K4me3, and enrichment of H3 histone-lysine-4 monomethylation (H3K4me1), resulting in a robust re-stimulatory immune response. The observations from the H4 modifications showed that besides H4K12ac and H4K20m3, all the assayed modifications were significantly higher in suboptimal convalescent fishes. The suboptimally challenged fish acquired more methylation along cytosine residues than the optimally infected fish. Together, these observations suggest that optimal temperature results in an immune priming effect, whereas the protection enabled in suboptimal convalescent fishes is operated through epigenetically controlled trained immune functions.

Addressing a Rule of Thumb: Modeling the Effects of Meteorological Conditions on Prescription of Antimicrobials in Aquaculture

Meteorological phenomena such as warm summer temperatures and increased numbers of sunlight hours have repeatedly been hypothesized to be associated with infectious diseases and an increased prescription of antimicrobial compounds in Danish aquaculture. To address this hypothesis, we prepared statistical models incorporating aquaculture production data from Danish Aquaculture, detailed records on prescription of antimicrobials from the Danish VETSTAT program, and meteorological data from 2001 to 2019 from the Danish Meteorological Institute. Separate series of models were made and refined for land-based and marine production, respectively. For both production forms, the models identify summer sunlight hours as having a significant influence on antimicrobial use. In addition to summer sunlight, spring sunlight and water temperature were integral, although not statistically significant, parameters when modeling antimicrobial use in marine production. Although the extensive availability and accuracy of relevant data are associated with Danish production, we believe the results allow for more general conclusions on the influence of meteorological parameters on outbreaks of bacterial pathogens in international aquaculture. Such insights could have a substantial impact on prophylactic strategies, fish husbandry, and our understanding of how increasing temperatures may affect future antimicrobial usage in the global aquaculture industry. IMPORTANCE Global aquaculture production has been rapidly increasing for decades and is set to play a pivotal role in feeding a growing human population. Along with the growth in aquaculture production, the annual global use of antimicrobials is estimated to increase by one-third between 2017 and 2030. Using detailed antimicrobial prescription records as a proxy for outbreaks, we were able to evaluate the effects of a variety of meteorological parameters through statistical modeling. Our results lend scientific support to informal observations from the industry, but more importantly, this study provides novel, essential information on the importance of abiotic factors that can, in turn, lead to improved prophylactic efforts and thus help to reduce antimicrobial use in global aquaculture.

Temperature effects on teleost immunity in the light of climate change

Temperature is an important environmental modulator of teleost immune activity. Susceptibility of teleosts to temperature variation depends on the species-specific adaptive temperature range, and the activity of the teleost immune system is generally temperature-dependent. Similar to many physiological and metabolic traits of ectotherms, temperature modulates the activity of immune traits. At low temperatures, acquired immunity of many teleost species is down-modulated, and their immuno-competence mainly depends on innate immunity. At intermediate temperatures, both innate and acquired immunity are fully active and provide optimal protection, including long-lasting immunological memory. When temperatures increase and reach the upper permissive range, teleost immunity is compromised. Moreover, temperature shifts may have negative effects on teleost immune functions, in particular if shifts occur rapidly with high amplitudes. On the contrary, short-term temperature increase may help teleost immunity to fight against pathogens transiently. A major challenge to teleosts therefore is to maintain immuno-competence throughout the temperature range they are exposed to. Climate change coincides with rising temperatures, and more frequent and more extreme temperature shifts. Both are likely to influence the immuno-competence of teleosts. Nonetheless, teleosts exist in habitats that differ substantially in temperature, ranging from below zero in the Arctic's to above 40°C in warm springs, illustrating their enormous potential to adapt to different temperature regimes. The present review seeks to discuss how changes in temperature variation, induced by climate change, might influence teleost immunity.

Aquaponics as a Promising Strategy to Mitigate Impacts of Climate Change on Rainbow Trout Culture

Simple Summary

Climate change and overexploitation of natural resources drive the need for innovative food production within a sustainability corridor. Aquaponics, combining the technology of recirculation aquaculture systems (RAS) and hydroponics in a closed-loop network, could contribute to addressing these problems. Aquaponic systems have lower freshwater demands than agriculture, greater land use efficiency, and decreased environmental impact combined with higher fish productivity. Rainbow trout is one of the major freshwater fish cultured worldwide, which, however, has not yet been commercially developed in aquaponics. Nevertheless, research conducted so far indicates that the trout species represents a good candidate for aquaponics.

Abstract

The impact of climate change on both terrestrial and aquatic ecosystems tends to become more progressively pronounced and devastating over the years. The sector of aquaculture is severely affected by natural abiotic factors, on account of climate change, that lead to various undesirable phenomena, including aquatic species mortalities and decreased productivity owing to oxidative and thermal stress of the reared organisms. Novel innovative technologies, such as aquaponics that are based on the co-cultivation of freshwater fish with plants in a sustainable manner under the context of controlled abiotic factors, represent a promising tool for mitigating the effect of climate change on reared fish. The rainbow trout (Oncorhynchus mykiss) constitutes one of the major freshwater-reared fish species, contributing to the national economies of numerous countries, and more specifically, to regional development, supporting mountainous areas of low productivity. However, it is highly vulnerable to climate change effects, mainly due to the concrete raceways, in which it is reared, that are constructed on the flow-through of rivers and are, therefore, dependent on water’s physical properties. The current review study evaluates the suitability, progress, and challenges of developing innovative and sustainable aquaponic systems to rear rainbow trout in combination with the cultivation of plants. Although not commercially developed to a great extent yet, research has shown that the rainbow trout is a valuable experimental model for aquaponics that may be also commercially exploited in the future. In particular, abiotic factors required in rainbow trout farming along, with the high protein proportion required in the ratios due to the strict carnivorous feeding behavior, result in high nitrate production that can be utilized by plants as a source of nitrogen in an aquaponic system. Intensive farming of rainbow trout in aquaponic systems can be controlled using digital monitoring of the system parameters, mitigating the obstacles originating from extreme temperature fluctuations.

Temperature affects settlement success of ectoparasitic salmon lice (Lepeophtheirus salmonis) and impacts the immune and stress response of Atlantic salmon (Salmo salar)

In this study, the effect of temperature on Atlantic salmon (Salmo salar) stress and immune response to the ectoparasitic salmon lice (Lepeophtheirus salmonis) was investigated. We found that infestation affected the expression of several immune and wound healing transcripts in the skin especially at the site of lice attachment compared to un-infested control fish. Moreover, expression patterns in the skin of infested fish suggest that host immune responses towards salmon lice are impaired at low temperatures. However, reduced lice infestation success and survival at the lowest investigated temperatures suggest that cold water temperatures are more detrimental to the lice than their fish hosts. Finally, temperature affected the stress response of the fish and infected fish had a higher increase in cortisol levels in response to handling (a stressor) than un-infested controls.

Comparative analysis on the immunoregulatory roles of ferritin M in hybrid fish (Carassius cuvieri ♀ × Carassius auratus red var ♂) and its parental species after bacterial infection

Ferritin M is involved in the regulation of fish immunity. In this study, open reading frame (ORF) sequences of ferritin M from hybrid fish and its parental species were 534 bp. Tissue-specific analysis indicated that the highest level of ferritin M from red crucian carp was observed in kidney, while peaked expressions of ferritin M from white crucian carp and hybrid carp were observed in gill. Elevated levels of ferritin M from hybrid carp and its parental species were detected in immune-related tissues following Aeromonas hydrophila infection or in cultured fish cell lines after lipopolysaccharide (LPS) challenge. Ferritin M overexpression could attenuate NF-κB and TNFα promoter activity in their respective fish cells. Purified ferritin M fusion proteins elicited in vitro binding activity to A. hydrophila and Edwardsiella tarda, lowered bacterial dissemination to tissues and alleviated inflammatory response. Furthermore, treatment with ferritin M fusion proteins could mitigate bacteria-induced liver damage and rescue antioxidant activity. These results suggested that ferritin M in hybrid fish showed a similar immune defense against bacteria infection in comparison with those of its parental species.

Critical review of the toxicity mechanisms of bisphenol F in zebrafish (Danio rerio): Knowledge gaps and future directions

Replacement chemicals for bisphenol A, such as bisphenol F (BPF), are detected in aquatic environments worldwide and can potentially exert negative effects on aquatic organisms. We synthesized peer-reviewed literature reporting molecular and physiological responses in zebrafish following exposure to BPF, as BPF is closely related to BPA structure and is a dominant replacement chemical in the marketplace. Global concentrations of BPF in aquatic environments were compiled and compared to physiological and behavioral impacts reported in zebrafish (e.g., developmental abnormalities, oxidative stress, immunotoxicity, endocrine disruption, and neurotoxicity). Using computational approaches, we elucidate BPF-mediated molecular networks and reveal novel biomarkers associated with BPF exposure. Functional classes of proteins including inflammatory cytokines, ATPases, peroxidases, and aromatic l-amino decarboxylases represent novel, underexplored targets of toxicity. Most revealing of this critical review is that few studies report biological responses to BPF at levels present in aquatic environments. Recommendations for future investigations based on knowledge gaps include: (1) Mechanistic studies in the central nervous system of zebrafish to address neurotoxicity; (2) Behavioral assays in zebrafish that assess the effects of BPF on anxiolytic, social, and fear-related behaviors; (3) Studies that broaden understanding of potential endocrine disrupting effects of BPF, for example insulin signaling is predicted to be sensitive to BPF exposure; (4) Studies into metabolic disruption with a focus on glutathione and aromatic amino acids, based upon pathway analysis data; (5) Studies utilizing mixture exposures with other BPA analogs to reflect environmental conditions more accurately.

Assassin snails (Anentome helena) as a biological model for exploring the effects of individual specialisation within generalist predators

Quantifying feeding behaviour of generalist predators at the population and individual levels is crucial for understanding the structure and functioning of food webs. Individual predator/consumer feeding niches can be significantly narrower than that of the population across animal taxa. In such species, the population of a generalist predator becomes essentially an ensemble of specialist individuals and this often highly affects the dynamics of the prey-predator interactions. Currently, few experimental systems exist that are both easily technically manipulated in a lab and are reliable to accurately assess effects of individual specialisation within generalist predators. Here we argue that a freshwater predaceous snail, Anentome helena (also known as an ‘assassin snail’), is a convenient and reliable experimental system to study feeding of a generalist predator on multiple food types which exhibits well-pronounced specialisation of foraging individuals. Using A. helena we experimentally test: (i) how relative prey abundances in the environment affect the feeding patterns, (ii) whether the feeding patterns are consistent over the duration of the experimental period, and (iii) compare the feeding niche breadth of individuals to that of the laboratory population. By offering four different prey snail species, at a range of relative abundances, we show that there are consistent patterns in feeding. Importantly, the consumption of each prey was independent of the relative abundance at which they were present. Individual predators showed selectivity to a particular prey, i.e. the population of assassin snails seems to be formed of individuals that specialise on different prey. Our findings would contribute to the recent revision and the ongoing debate on the classification of predator species into generalists and specialists.

A New Insight Into the Underlying Adaptive Strategies of Euryhaline Marine Fish to Low Salinity Environment Through Cholesterol Nutrition to Regulate Physiological Responses

Salinity is an important environmental factor that can affect the metabolism of aquatic organisms, while cholesterol can influence cellular membrane fluidity which are vital in adaption to salinity changes. Hence, a 4-week feeding trial was conducted to evaluate the effects of water salinity (normal 23 psu and low 5 psu) and three dietary cholesterol levels (CH0.16, 0.16%, CH1.0, 1.0% and CH1.6, 1.6%) on osmoregulation, cholesterol metabolism, fatty acid composition, long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis, oxidative stress (OS), and endoplasmic reticulum stress (ERS) of the euryhaline fish black seabream (Acanthopagrus schlegelii). The results indicated that in low salinity, fish fed with the CH1.0 diet improved ion reabsorption and osmoregulation by increased Na+ concentration in serum as well as expression levels of osmoregulation-related gene expression levels in gills. Both dietary cholesterol level and water salinity significantly affected most cholesterol metabolic parameters in the serum and tissues, and the results showed that low salinity promoted cholesterol synthesis but inhibited cholesterol catabolism. Besides, in low salinity, hepatic expression levels of LC-PUFA biosynthesis genes were upregulated by fed dietary cholesterol supplementation with contents of LC-PUFAs, including EPA and DHA being increased. Malondialdehyde (MDA) was significantly increased in low-salinity environment, whereas MDA content was decreased in fish fed with dietary CH1.0 by activating related antioxidant enzyme activity and gene expression levels. A similar pattern was recorded for ERS, which stimulated the expression of nuclear factor kappa B (nf-κb), triggering inflammation. Nevertheless, fish reared in low salinity and fed with dietary CH1.0 had markedly alleviated ERS and downregulated gene expression levels of pro-inflammatory cytokines. Overall, these findings demonstrate that cholesterol, as an important nutrient, plays vital roles in the process of adaptation to low salinity of A. schlegelii, and provides a new insight into underlying adaptive strategies of euryhaline marine fish reared in low salinity.

Expression of p38MAPK and its regulation of apoptosis under high temperature stress in the razor clam Sinonovacula constricta

p38MAPK is a key branch of the MAPK (mitogen-activated protein kinase) pathway that plays an important role in physiological processes such as apoptosis, cell proliferation and growth. In this experiment, we screened and identified one p38MAPK gene in the razor clam Sinonovacula constricta, which encoded 359 amino acids and was widely expressed in various adult tissues. After 24 h of high temperature stress at 34 °C, the transcript expression of p38MAPK showed significant changes in all tested tissues. In particular in the gill and hepatopancreas tissues, where the expression increased 1.81 and 7.83 times compared with the control group, respectively (P < 0.01). Furthermore, we examined the expression of the apoptosis suppressor gene Bcl-2 and pro-apoptosis gene Bax by knock-down of p38MAPK with dsRNA interference in the gill and hepatopancreas tissues. The obvious up-regulation expression of Bcl-2 and significant suppression of Bax were observed, respectively (P < 0.01). Moreover, the TUNEL staining technique was used to detect apoptosis before and after interference. The degree of apoptosis in the gill and hepatopancreas tissues was reduced after interference with p38MAPK, and the ROS content was significantly reduced (P < 0.01). The results suggested that p38MAPK had a regulatory role in the heat tolerance of razor clams.

Ocean Warming Leads to Increases in Aerobic Demand and Changes to Gene Expression in the Pinfish (Lagodon rhomboides)

Anthropogenic climate change is causing increases in the frequency, intensity, and duration of marine heatwaves (MHWs). These short-term warming events can last for days to weeks and can produce severe disruptions in marine ecosystems, as many aquatic species are poikilotherms that depend on the conditions of the environment for physiological processes. It is crucial to investigate the effects of these thermal fluctuations on species that play a disproportionate ecological role in marine ecosystems, such as the pinfish (Lagodon rhomboides) in the Gulf of Mexico and western Atlantic. In this study, we exposed pinfish to a simulated MHW in aquaria and examined the impacts of acute warming on two life stages (juvenile and adult), measuring oxygen consumption and gene expression in two relevant tissue types (liver and muscle). We saw significant increases in routine metabolic rate with increasing temperature in both juveniles (24.58 mgO2/kg/h increase per 1°C of warming) and adults (10.01 mgO2/kg/h increase per 1°C of warming). These results indicate that exposure to increased temperatures was more metabolically costly for juveniles than for adults, on a mass-specific basis. This was also observed in the molecular analyses, where the largest number of differentially expressed genes were observed in the juvenile pinfish. The analyses of gene expression suggest warming produces changes to immune function, cell proliferation, muscle contraction, nervous system function, and oxygen transport. These results indicate that this ecologically relevant species will be significantly impacted by projected increases in frequency and magnitude of MHWs, particularly in the juvenile stage.

Glyphosate damages blood-testis barrier via NOX1-triggered oxidative stress in rats: Long-term exposure as a potential risk for male reproductive health

Blood-testis barrier (BTB) creates a privileged niche indispensable for spermatogenesis. Glyphosate (GLY), the most commonly used herbicide worldwide, has been reported to decrease sperm quality. However, whether and how GLY destroys the BTB to affect sperm quality remains to be elucidated. Herein, this study was designed to investigate the influence of GLY on the BTB in vivo and in vitro experiments. The results showed that male rats exposed to GLY for 4 months exhibited a decrease in sperm quality and quantity, accompanied by BTB integrity disruption and testicular oxidative stress. Additionally, GLY-induced reactive oxygen species (ROS) contributed to the downregulation of BTB-related proteins in primary Sertoli cells (SCs). Intriguingly, we identified a marked upregulation of oxidative stress-related gene NOX1 in GLY-exposed testis based on transcriptome analysis. NOX1 knockdown blocked the GLY-induced oxidative stress, as well as prevented BTB-related protein decrease in SCs. Furthermore, the estrogen receptor (ER)-α was significantly upregulated in vivo and in vitro models. An ER-α inhibitor decreased the expression levels of both ER-α and NOX1. Mechanistically, GLY directly interacted with ER-α at the site of Pro39 and Lys401 to promote ER-α activation, which boosted NOX1 expression to trigger ROS accumulation. Collectively, these results demonstrate that long-term GLY exposure adversely affects BTB integrity, which disrupts spermatogenesis via activation of ER-α/NOX1 axis. This study presents a better understanding of the risk of long-term GLY exposure to male fertility.

Blood cell characterization and transcriptome analysis reveal distinct immune response and host resistance of different ploidy cyprinid fish following Aeromonas hydrophila infection

Aeromonas hydrophila can pose a great threat to survival of freshwater fish. In this study, A. hydrophila infection could decrease blood cell numbers, promote blood cell damage as well as alter the levels of alkaline phosphatase (ALP), lysozyme (LZM), aspartate aminotransferase (AST), total antioxidant capacity (T-AOC), total superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA) in immune-related tissues of red crucian carp (RCC, 2 N = 100) and triploid cyprinid fish (3 N fish, 3 N = 150). In addition, the significant alternation of antioxidant status was observed in PBMCs isolated from RCC and 3 N following LPS stimulation. The core differential expression genes (DEGs) involved in apoptosis, immunity, inflammation and cellular signals were co-expressed differentially in RCC and 3 N following A. hydrophila challenge. NOD-like receptor (NLR) signals appeared to play a critical role in A. hydrophila-infected fish. DEGs of NLR signals in RCCah vs RCCctl were enriched in caspase-1-dependent Interleukin-1β (IL-1β) secretion, interferon (IFN) signals as well as cytokine activation, while DEGs of NLR signals in 3Nah vs 3Nctl were enriched in caspase-1-dependent IL-1β secretion and antibacterial autophagy. These results highlighted the differential signal regulation of different ploidy cyprinid fish to cope with bacterial infection.

A novel ferritin L (FerL) in hybrid crucian carp could participate in host defense against Aeromonas hydrophila infection and diminish inflammatory signals

FerL, a multifunctional iron-storage polypeptide, not only exhibited a regulatory role in iron metabolism, but also participated in the regulation of fish immunity. In this study, ORF sequence of WR-FerL was 522 bp, encoding 173 amino acid residues. Tissue-specific analysis revealed that the highest expression of WR-FerL was detected in spleen. A. hydrophila challenge and LPS stimulation could sharply enhance WR-FerL mRNA expression in tissues and fish cells, respectively. Purified WR-FerL fusion peptide exhibited in vitro binding activity to A. hydrophila and endotoxin, limited bacterial dissemination to tissues as well as attenuated A. hydrophila-induced production of pro-inflammatory cytokines. Moreover, WR-FerL overexpression could abrogate NF-κB and TNFα promoter activity in fish cells. These results indicated that WR-FerL could play an important role in host defense against A. hydrophila infection.

Ferritin H can counteract inflammatory response in hybrid fish and its parental species after Aeromonas hydrophila infection

Ferritin H can participate in the regulation of fish immunity. Tissue-specific analysis revealed that the highest expressions of Ferritin H in parental species were observed in spleen, while peaked level of Ferritin H mRNA in hybrid fish was observed in liver. In addition, A. hydrophila challenge could sharply enhance their Ferritin H mRNA expression in liver, kidney and spleen. To further investigate their roles in immune regulation, their Ferritin H fusion proteins were produced in vitro. Ferritin H fusion proteins could exhibit a direct binding activity to A. hydrophila and endotoxin in a dose-dependent manner, restrict dissemination of A. hydrophila to tissues and abrogate inflammatory cascades. Moreover, treatment with Ferritin H fusion proteins could reduce A. hydrophila-induced lipid peroxidation. These results indicated that Ferritin H in hybrid fish elicited a similar immune regulation of A. hydrophila-induced inflammatory signals in comparison with those of its parents.

Toxicity of amine-functionalized single-carbon nanotube (NH2 f-SWCNT) to Channel Catfish (Ietalurus Punetaus): Organ pathologies, oxidative stress, inflammation, and apoptosis

The rapid development of carbon nanotubes (CNTs) in the field of fish disease control and prevention raises concerns about the toxicity and safe use in fish. This study was performed to assess the effect on histological changes, oxidative stress related markers in response to various concentrations of amine-functionalized single carbon nanotubes (NH₂ f-SWCNT) (1, 10 and 100 mg kg^-1 fish) in Channel Catfish (Ietalurus Punetaus) for up to 10 days. Moreover, pro-inflammatory cytokine genes and apoptotic genes were analyzed to obtain a better understanding of molecular mechanism of NH₂ f-SWCNT induced toxicity. As a result, intraperitoneal (i.p.) administration of NH₂ f-SWCNT caused dose-dependent and time-dependent injuries in the sampled tissues. In comparison with the control groups, decrease of catalase (CAT) activity and superoxide dismutase (SOD), and increase of malondialdehyde (MDA) and lactin dehydrogenase (LDH) were observed in all treatments. Real-time PCR assay showed inflammatory response with dose-dependent increase of tumor necrosis factor alpha (TNFα) and transient increase of interleukin 1β (IL-1β) in the liver. NH₂ f-SWCNT administration induced increase of p38 as well as caspase-3 in all treatments compared to the control groups, indicating the involvement of p38-MAPK cascade and caspase-3 cascade in liver cell apoptosis. Overall, we conclude that NH₂ f-SWCNT exert effects by direct injury and indirectly oxidative stress, resulting in inflammation and apoptosis, which provides data for understanding of the biological mechanisms underlying the toxicity of CNTs in fish.

Effect of Lipopolysaccharide (LPS) stimulation on apoptotic process and oxidative stress in fibroblast cell of hybrid crucian carp compared with those of Carassius cuvieri and Carassius auratus red var

Bacterial LPS is a heat-stable endotoxin and wall components of gram negative bacteria, which can exhibit a toxicological effect on physiology and biochemical activities of fish. In this study, we investigated the effect of LPS exposure on cell viability, oxidative stress, caspase activity and immune-related gene expressions in cultured fin cell lines of red crucian carp, white crucian carp and their hybrid offspring. LPS stimulation could reduce fish cell viability, whereas gene expression levels and promoter activities in inflammatory signals increased dramatically. Moreover, enhanced levels of intracellular oxidative stress and decreased levels of mitochondrial membrane potential (MMP) were observed in LPS-induced fish cells. N-Acetyl-L-cysteine (NAC) could alleviate LPS-stimulated reactive oxygen species (ROS) generation and caspase-3 activity in fish cells. These results suggested that ROS-mediated cytotoxic stress was involved in LPS-induced inflammation and mitochondrial damage in cultured fish cells.

Mediterranean Aquaculture in a Changing Climate: Temperature Effects on Pathogens and Diseases of Three Farmed Fish Species

Climate change is expected to have a drastic effect on aquaculture worldwide. As we move forward with the agenda to increase and diversify aquaculture production, rising temperatures will have a progressively relevant impact on fish farming, linked to a multitude of issues associated with fish welfare. Temperature affects the physiology of both fish and pathogens, and has the potential to lead to significant increases in disease outbreaks within aquaculture systems, resulting in severe financial impacts. Significant shifts in future temperature regimes are projected for the Mediterranean Sea. We therefore aim to review and discuss the existing knowledge relating to disease outbreaks in the context of climate change in Mediterranean finfish aquaculture. The objective is to describe the effects of temperature on the physiology of both fish and pathogens, and moreover to list and discuss the principal diseases of the three main fish species farmed in the Mediterranean, namely gilthead seabream (Sparus aurata), European seabass (Dicentrarchus labrax), and meagre (Argyrosomus regius). We will attempt to link the pathology of each disease to a specific temperature range, while discussing potential future disease threats associated with the available climate change trends for the Mediterranean Sea.

Immunotoxicological effects of insecticides in exposed fishes

Biologically active compounds used in agriculture that develop near aquatic environments easily spill into rivers or lakes. As a result, insecticides, herbicides and fungicides are observed worldwide in aquatic environments and accumulated in aquatic organism. Many insecticides, including organochlorine and organophosphate, have long been banned long ago because of their high persistence and non-target toxicity. However, previous studies have shown that persistent pesticides remain in aquatic organisms. The immune system is the first defense mechanism against exposure to persistent organic pollutants or pesticides that have been released into the aquatic environment. Many insecticides have been reported to cause immunotoxicity, which is represented by alteration of phagocytic and lysozyme activity. Recent studies show that immunotoxicity by insecticides exerts a more complex mechanism in fish. Insecticides induce immunotoxic effects, such as the release of inflammatory cytokines from head kidney macrophages and inhibition of immune cell proliferation in fish, which can lead to death in severe cases. Even currently used pesticides, such as pyrethroid, with low bioaccumulation have been shown to induce immunotoxicological effects in fish when exposed continuously. Therefore, this review describes the types and bioaccumulation of insecticides that cause immunotoxicity and detailed immunotoxicological mechanisms in fish tissues.

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).

Innate immunity, oxidative stress and body indices of Eurasian perch Perca fluviatilis after two weeks of exposure to artificial light at night

Artificial light at night (ALAN) can disrupt biological rhythms of fish and other vertebrates by changing the light information of the nocturnal environment. Disrupted biorhythms can impair the immune system of vertebrates as it has been shown for conditions with continuous illumination or long-day photoperiod in many vertebrates, including fish. Nonetheless, this has not been shown so far for typical ALAN scenarios with high light intensities during day and low light intensities at night. Therefore, in this study, proxies for the innate immune system and oxidative stress as well as body indices of Eurasian perch Perca fluviatilis were measured under a wide range of intensities of nocturnal illumination. The authors found no changes in parameters of the innate immune system and no significant changes in proxies for oxidative stress after 2-week exposures to nocturnal illuminance ranging from 0.01 lx to 1 lx in one experiment or from 1 lx to 100 lx in a second experiment. A decrease in the hepato-somatic index at the highest tested light intensity of 100 lx compared to the dark control was the only significant difference in all parameters among treatments. After 2 weeks of exposure, ALAN does not seem to seriously challenge the innate immune system and seems to cause less oxidative stress than expected. The results of this study contradict the findings from other studies applying continuous illumination or long-day photoperiod and highlight the importance of further research in this field. Because ALAN represents a sustained modulation of the environment that may have cumulative effects over time, long-term studies are required for a better understanding of how ALAN modulates the health of fish.

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

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

Zoonotic spillover: Understanding basic aspects for better prevention

The transmission of pathogens from wild animals to humans is called “zoonotic spillover”. Most human infectious diseases (60-75%) are derived from pathogens that originally circulated in non-human animal species. This demonstrates that spillover has a fundamental role in the emergence of new human infectious diseases. Understanding the factors that facilitate the transmission of pathogens from wild animals to humans is essential to establish strategies focused on the reduction of the frequency of spillover events. In this context, this article describes the basic aspects of zoonotic spillover and the main factors involved in spillover events, considering the role of the inter-species interactions, phylogenetic distance between host species, environmental drivers, and specific characteristics of the pathogens, animals, and humans. As an example, the factors involved in the emergence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pandemic are discussed, indicating what can be learned from this public health emergency, and what can be applied to the Brazilian scenario. Finally, this article discusses actions to prevent or reduce the frequency of zoonotic spillover events.

Metabolomics analysis of the effects of temperature on the growth and development of juvenile European seabass (Dicentrarchus labrax)

Temperature variations have significant impacts on the growth and development of fish. In this study, the effects of temperature on the growth and development of European seabass (Dicentrarchus labrax) were investigated using ultra-performance liquid chromatography-tandem mass spectrometry-based metabolomics. Three groups of fish were exposed to various temperatures for 60 days: T1-E (10 °C), T2-E (15 °C), and T3-E (20 °C). Afterward, the temperature of all groups was increased to 20 °C and maintained for 62 days (T1-S, T2-S, T3-S). The livers were extracted for subsequent analysis. In the first stage of the experiment, the growth rate was highest in the T3-E group, followed by the T1-E and T2-E groups. The following metabolites identified by comparative analysis were found to be elevated: L-thyroxine, cysteamine, uridine diphosphate (UDP)-glucose, α-ketoglutaric acid, carbamoyl phosphate, and guanidine acetic acid of the T1-E group. Pathway analysis of the altered metabolites suggested changes in glucose metabolism, arginine and proline metabolism, the tricarboxylic acid cycle, the ornithine cycle, histidine metabolism, and taurine metabolism, which were involved with growth and development. Meanwhile, partial compensatory growth was observed in fish in the T1-S and T2-S groups. Metabolites identified as potential markers of growth included L-cysteine, taurocholic acid, UDP-glucose, and L-thyroxine. The significantly changed metabolic pathways were cysteine and methionine metabolism, bile secretion, tyrosine metabolism, and hypotaurine metabolism. We screened out the marker metabolites and metabolic pathway could provide important insights into the potential mechanisms of temperature affects the growth and development of European seabass. All in all, our research can provide theoretical basis and technical guidance for efficiently culturing European seabass.