Adverse Husbandry of Maraena Whitefish Directs the Immune System to Increase Mobilization of Myeloid Cells and Proinflammatory Responses

Are bold-shy personalities of European perch (Perca fluviatilis) linked to stress tolerance and immunity? A scope of harnessing fish behavior in aquaculture

The sensitivity to stress and its impact on immunity are supposedly related to a fish's personality. In the present study, European perch (Perca fluviatilis) were exposed to an open-field and a novel-object test to identify distinctive shy and bold individuals. This series of cognitive tests revealed clear differences between proactive individuals with pronounced exploration behavior (bold personality) and reactive individuals that took a freeze-hide position (shy personality). A cohort of shy and bold perch was then exposed to elevated stocking density. Frozen activity and lower explorative behavior were related to higher basal and stocking-induced cortisol levels compared to proactive individuals. Since cortisol is a well-known modulator of immune-gene expression, we used multiplex real-time PCR to profile the differential immune responses to the intraperitoneal injection of Aeromonas hydrophila in the head kidney and peritoneal cells of bold and shy perch individuals. These expression differences between stimulated bold and shy perch were generally modest, except for the genes encoding the complement component c3 and the matrix metallopeptidase mmp9. The strong differential expression of these two bactericidal and inflammatory genes in the context of the modestly regulated features suggests that a fish's personality is linked to a particular immune-defense strategy. In conclusion, our approach, based on behavioral video observations, phagocytosis and enzyme assays, immunogene-expression profiling, and quantification of stress-relevant metabolites, revealed indications for divergent coping styles in cohorts of bold or shy European perch. This divergence could be exploited in future selective breeding programs.

Red blood cells in proliferative kidney disease-rainbow trout (Oncorhynchus mykiss) infected by Tetracapsuloides bryosalmonae harbor IgM+ red blood cells

The myxozoan parasite Tetracapsuloides bryosalmonae is the causative agent of proliferative kidney disease (PKD)-a disease of salmonid fishes, notably of the commercially farmed rainbow trout Oncorhynchus mykiss. Both wild and farmed salmonids are threatened by this virulent/deadly disease, a chronic immunopathology characterized by massive lymphocyte proliferation and hyperplasia, which manifests as swollen kidneys in susceptible hosts. Studying the immune response towards the parasite helps us understand the causes and consequences of PKD. While examining the B cell population during a seasonal outbreak of PKD, we unexpectedly detected the B cell marker immunoglobulin M (IgM) on red blood cells (RBCs) of infected farmed rainbow trout. Here, we studied the nature of this IgM and this IgM⁺ cell population. We verified the presence of surface IgM via parallel approaches: flow cytometry, microscopy, and mass spectrometry. The levels of surface IgM (allowing complete resolution of IgM^- RBCs from IgM⁺ RBCs) and frequency of IgM⁺ RBCs (with up to 99% of RBCs being positive) have not been described before in healthy fishes nor those suffering from disease. To assess the influence of the disease on these cells, we profiled the transcriptomes of teleost RBCs in health and disease. Compared to RBCs originating from healthy fish, PKD fundamentally altered RBCs in their metabolism, adhesion, and innate immune response to inflammation. In summary, RBCs play a larger role in host immunity than previously appreciated. Specifically, our findings indicate that the nucleated RBCs of rainbow trout interact with host IgM and contribute to the immune response in PKD.

Experimental Handling Challenges Result in Minor Changes in the Phagocytic Capacity and Transcriptome of Head-Kidney Cells of the Salmonid Fish Coregonus maraena

Aquaculture management involves regular handling procedures, but these can evoke stress responses in farmed fish. We compiled an extensive list of published parameters that indicate the most likely handling-induced physiological deviations from the norm. However, since these parameters are based almost exclusively on studies of rainbow trout and Atlantic salmon, we conducted a handling-challenge experiment with maraena whitefish (Coregonus maraena). This salmonid fish was sampled at either 3 or 24 h after a single 1-min handling or after 10 days of daily repeated 1-min handling. The cortisol levels were strongly elevated in some individuals at 3 h after the single handling challenge, but these elevations were not significantly different between the challenged and control cohorts. The phagocytic capacity of myeloid head-kidney cells stimulated with fluorophore-labeled, inactivated Aeromonas salmonicida was significantly decreased in maraena whitefish at 3 h after the handling challenge compared to control fish. Microarray analysis of head-kidney samples from the challenged and control fish revealed 12 differentially expressed genes at 3 h and 70 at 24 h after the single handling episode, but only 5 differentially expressed genes after 10 days of repeated daily handling. The identified genes were assigned to numerous stress- and immune-relevant functional pathways, including “glucocorticoid receptor signaling” (3 h post-challenge), “HIF1A signaling” (24 h post-challenge), or “complement system” (10 days of repeated challenge). Our data reveal the tight interconnection of immune and stress pathways in the head kidney of maraena whitefish and corroborate several parameters previously found regulated in other tissues of handling-stressed rainbow trout. These findings indicate that handling may compromise the health and welfare of maraena whitefish in aquaculture.

A Multidisciplinary Approach Evaluating Soybean Meal-Induced Enteritis in Rainbow Trout Oncorhynchus mykiss

This study evaluated a diverse range of markers of feeding stress to obtain a more precise assessment of the welfare of rainbow trout in relation to inadequate husbandry conditions. A feeding stress model based on dietary soybean meal was employed to identify suitable minimally invasive “classical” stress markers, together with molecular signatures. In a 56-day feeding experiment, rainbow trout were fed diets containing different levels of soybean meal. The impact of these different soybean meal diets on rainbow trout was assessed by water quality analyses, clinical health observations, classic growth and performance parameters, gut histopathology, blood-parameter measurements and multigene-expression profiling in RNA from whole blood. Soybean meal-induced enteritis was manifested phenotypically by an inflammatory reaction in the posterior section of the intestine and by diarrhoea in some trout. These inflammatory changes were associated with decreased supranuclear vacuolation. The haematocrit values and the levels of plasma cortisol and circulating lymphocytes in the blood were increased in trout that had consumed high amounts of SBM. Notably, the increased haematocrit depended significantly on the bodyweight of the individual trout. The transcript levels of certain genes (e.g., MAP3K1, LYG, NOD1, STAT1 and HSP90AB) emerged as potentially useful indicators in the blood of rainbow trout providing valuable information about inadequate nutrition. The expression-profiling findings provide a basis for improved, minimally invasive monitoring of feeding regimens in trout farming and may stimulate the development of practical detection devices for innovative aquaculture operations.

Resting parasympathetic nervous system activity is associated with greater antiviral gene expression

Parasympathetic nervous system activity can downregulate inflammation, but it remains unclear how parasympathetic nervous system activity relates to antiviral activity. The present study examined associations between parasympathetic nervous system activity and cellular antiviral gene regulation in 90 adolescents (M_age = 16.28, SD = 0.73; 51.1% female) who provided blood samples and measures of cardiac respiratory sinus arrhythmia (RSA), twice, five weeks apart. Using a multilevel analytic framework, we found that higher RSA (an indicator of higher parasympathetic nervous system activity)-both at rest and during paced breathing-was associated with higher expression of Type I interferon (IFN) response genes in circulating leukocytes, even after adjusting for demographic and biological covariates. RSA was not associated with a parallel measure of inflammatory gene expression. These results identify a previously unrecognized immunoregulatory aspect of autonomic nervous system function and highlight a potential biological pathway by which parasympathetic nervous system activity may relate to health.

Traumatic events and mental health: The amplifying effects of pre-trauma systemic inflammation

BACKGROUND

Traumatic experiences are strongly predictive of adverse mental health outcomes. Experimental studies have demonstrated that systemic inflammation can increase reactivity to threatening stimuli. It is not known whether naturally occurring inflammation amplifies the impact of traumatic experiences on mental health. Here we test whether incident traumatic events are more predictive of adverse mental health outcomes for individuals with greater pre-trauma systemic inflammation in a racially and ethnically diverse cohort study of youth assigned male at birth who identify as sexual or gender minorities (ages 16-29, n = 518), a group at high risk for trauma exposure.

METHODS

Measures of inflammation, depression symptom severity, and perceived stress were measured at baseline. One year later, depression symptom severity and perceived stress were measured again, and participants reported the traumatic events they had experienced in the intervening year.

RESULTS

In a model adjusted for baseline depression symptom severity and other key covariates, we found that higher baseline levels of interleukin-1β amplified the effect of incident trauma exposure on depression symptom severity at follow-up (β = 0.234, SE = 0.080, P = 0.004). In a model adjusted for baseline perceived stress and other key covariates, we found that higher baseline scores on a multi-marker inflammatory index amplified the effect of incident trauma exposure on perceived stress at follow-up (β = 0.243, SE = 0.083, P = 0.003).

CONCLUSIONS

These findings suggest that greater pre-trauma inflammation may predict poorer mental health following trauma exposure. Understanding how inflammation interacts with trauma to shape mental health may generate novel insights for preventing and treating the debilitating psychological consequences of trauma.

Effects of Chronic Hypoxia on the Immune Status of Pikeperch (Sander lucioperca Linnaeus, 1758)

Simple Summary

Inadequate oxygen saturation, or hypoxia, belongs to one of the critical stress factors in intensive aquaculture. Exposure of fish to low oxygen levels over prolonged periods substantially affects their well-being and immune competence, resulting in increased disease susceptibility and consequent economic losses. In this interdisciplinary research, we aimed to provide a deeper understanding of the effect of chronic low oxygen saturation on pikeperch farmed in recirculating aquaculture systems. The obtained data offer unprecedented insights into the changes in the immunocompetence of studied fish and suggest high robustness of this new aquaculture species to the stress factors of intensive aquaculture.

Abstract

Inadequate oxygen saturation can induce stress responses in fish and further affect their immunity. Pikeperch, recently introduced in intensive aquaculture, is suggested to be reared at nearly 100% DO (dissolved oxygen), yet this recommendation can be compromised by several factors including the water temperature, stocking densities or low circulation. Herein, we aimed to investigate the effect of low oxygen saturation of 40% DO (±3.2 mg/L) over 28 days on pikeperch farmed in recirculating aquaculture systems. The obtained data suggest that—although the standard blood and health parameters did not reveal any significant differences at any timepoint—the flow cytometric analysis identified a slightly decreased proportion of lymphocytes in the HK (head kidney) of fish exposed to hypoxia. This has been complemented by marginally downregulated expression of investigated immune and stress genes in HK and liver (including FTH1, HIF1A and NR3C1). Additionally, in the model of acute peritoneal inflammation induced with inactivated Aeromonas hydrophila, we observed a striking dichotomy in the sensitivity to the low DO between innate and adaptive immunity. Thus, while the mobilization of myeloid cells from HK to blood, spleen and peritoneal cavity, underlined by changes in the expression of key proinflammatory cytokines (including MPO, IL1B and TNF) was not influenced by the low DO, hypoxia impaired the influx of lymphocytes to the peritoneal niche in the later phases of the immune reaction. Taken together, our data suggest high robustness of pikeperch towards the low oxygen saturation and further encourage its introduction to the intensive aquaculture systems.

Blood Will Tell: What Hematological Analyses Can Reveal About Fish Welfare

Blood analyses provide substantial information about the physiological aspects of animal welfare assessment, including the activation status of the neuroendocrine and immune system, acute and long-term impacts due to adverse husbandry conditions, potential diseases, and genetic predispositions. However, fish blood is still not routinely analyzed in research or aquaculture for the assessment of health and/or welfare. Over the years, the investigative techniques have evolved from antibody-based or PCR-based single-parameter analyses to now include transcriptomic, metabolomic, and proteomic approaches and from hematological observations to fluorescence-activated blood cell sorting in high-throughput modes. The range of testing techniques established for blood is now broader than for any other biogenic test material. Evaluation of the particular characteristics of fish blood, such as its cell composition, the nucleation of distinct blood cells, or the multiple isoforms of certain immune factors, requires adapted protocols and careful attention to the experimental designs and interpretation of the data. Analyses of fish blood can provide an integrated picture of the endocrine, immunological, reproductive, and genetic functions under defined environmental conditions and treatments. Therefore, the scarcity of high-throughput approaches using fish blood as a test material for fish physiology studies is surprising. This review summarizes the wide range of techniques that allow monitoring of informative fish blood parameters that are modulated by different stressors, conditions, and/or treatments. We provide a compact overview of several simple plasma tests and of multiparametric analyses of fish blood, and we discuss their potential use in the assessment of fish welfare and pathologies.

Fish Pathology Research and Diagnosis in Aquaculture of Farmed Fish; a Proteomics Perspective

One of the main constraints in aquaculture production is farmed fish vulnerability to diseases due to husbandry practices or external factors like pollution, climate changes, or even the alterations in the dynamic of product transactions in this industry. It is though important to better understand and characterize the intervenients in the process of a disease outbreak as these lead to huge economical losses in aquaculture industries. High-throughput technologies like proteomics can be an important characterization tool especially in pathogen identification and the virulence mechanisms related to host-pathogen interactions on disease research and diagnostics that will help to control, prevent, and treat diseases in farmed fish. Proteomics important role is also maximized by its holistic approach to understanding pathogenesis processes and fish responses to external factors like stress or temperature making it one of the most promising tools for fish pathology research.

Time-Dependent Effects of Acute Handling on the Brain Monoamine System of the Salmonid Coregonus maraena

The immediate stress response involves the activation of the monoaminergic neurotransmitter systems including serotonin, dopamine and noradrenaline in particular areas of the fish brain. We chose maraena whitefish as a stress-sensitive salmonid species to investigate the influence of acute and chronic handling on the neurochemistry of monoamines in the brain. Plasma cortisol was quantified to assess the activation of the stress axis. In addition, we analyzed the expression of 37 genes related to the monoamine system to identify genes that could be used as markers of neurophysiological stress effects. Brain neurochemistry responded to a single handling (1 min netting and chasing) with increased serotonergic activity 3 h post-challenge. This was accompanied by a modulated expression of monoaminergic receptor genes in the hindbrain and a significant increase of plasma cortisol. The initial response was compensated by an increased monoamine synthesis at 24 h post-challenge, combined with the modulated expression of serotonin-receptor genes and plasma cortisol concentrations returning to control levels. After 10 days of repeated handling (1 min per day), we detected a slightly increased noradrenaline synthesis and a down-regulated expression of dopamine-receptor genes without effect on plasma cortisol levels. In conclusion, the changes in serotonergic neurochemistry and selected gene-expression profiles, together with the initial plasma cortisol variation, indicate an acute response and a subsequent recovery phase with signs of habituation after 10 days of daily exposure to handling. Based on the basal expression patterns of particular genes and their significant regulation upon handling conditions, we suggest a group of genes as potential biomarkers that indicate handling stress on the brain monoamine systems.

The synergistic interaction of thermal stress coupled with overstocking strongly modulates the transcriptomic activity and immune capacity of rainbow trout (Oncorhynchus mykiss)

The objective of the present study is to identify and evaluate informative indicators for the welfare of rainbow trout exposed to (A) a water temperature of 27 °C and (B) a stocking density of 100 kg/m³ combined with a temperature of 27 °C. The spleen-somatic and condition index, haematocrit and the concentrations of haemoglobin, plasma cortisol and glucose revealed non-significant differences between the two stress groups and the reference group 8 days after the onset of the experiments. The transcript abundance of almost 1,500 genes was modulated at least twofold in in the spleen of rainbow trout exposed to a critical temperature alone or a critical temperature combined with crowding as compared to the reference fish. The number of differentially expressed genes was four times higher in trout that were simultaneously challenged with high temperature and crowding, compared to trout challenged with high temperature alone. Based on these sets of differentially expressed genes, we identified unique and common tissue- and stress type-specific pathways. Furthermore, our subsequent immunologic analyses revealed reduced bactericidal and inflammatory activity and a significantly altered blood-cell composition in challenged versus non-challenged rainbow trout. Altogether, our data demonstrate that heat and overstocking exert synergistic effects on the rainbow trout’s physiology, especially on the immune system.

Characterization of Sialic Acid-Binding Immunoglobulin-Type Lectins in Fish Reveals Teleost-Specific Structures and Expression Patterns

The cellular glycocalyx of vertebrates is frequently decorated with sialic acid residues. These sialylated structures are recognized by sialic acid-binding immunoglobulin-type lectins (Siglecs) of immune cells, which modulate their responsiveness. Fifteen Siglecs are known to be expressed in humans, but only four Siglecs are regularly present in fish: Siglec1, CD22, myelin-associated glycoprotein (MAG), and Siglec15. While several studies have dealt with the physiological roles of these four Siglecs in mammals, little is known about Siglecs in fish. In the present manuscript, the expression landscapes of these Siglecs were determined in the two salmonid species Oncorhynchus mykiss and Coregonus maraena and in the percid fish Sander lucioperca. This gene-expression profiling revealed that the expression of MAG is not restricted to neuronal cells but is detectable in all analyzed blood cells, including erythrocytes. The teleostean MAG contains the inhibitory motif ITIM; therefore, an additional immunomodulatory function of MAG is likely to be present in fish. Besides MAG, Siglec1, CD22, and Siglec15 were also expressed in all analyzed blood cell populations. Interestingly, the expression profiles of genes encoding Siglecs and particular associated enzymes changed in a gene- and tissue-specific manner when Coregonus maraena was exposed to handling stress. Thus, the obtained data indicate once more that stress directly affects immune-associated processes.

Early response of salmonid head-kidney cells to stress hormones and toll-like receptor ligands

The functional spectrum of the teleostean head kidney covers haematopoietic, immune and endocrine signalling pathways with physiological effects that are likely to conflict if activated at the same time. An in vivo experiment on the salmonid fish maraena whitefish (Coregonus maraena) revealed that the head kidney shows a remarkably strong response after injection of Aeromonas salmonicida within 48 h. In order to investigate the potential influence of endocrine signalling on the initiation of immune responses, we established a primary culture of head-kidney cells of maraena whitefish. For the characterisation of this model system, we used flow cytometry complemented with an extensive panel of immunological/haematological and stress-physiological/neuroendocrinological qPCR assays. More than one third of the cells expressed the characteristic signature of myeloid cells, while more than half of the cells expressed those genes typical for lymphocytes and monocytes. In parallel, we quantified the expression of genes encoding endocrine receptors and identified ADRA2D as by far the most highly expressed adrenergic-receptor gene in head-kidney cells. The stimulation of the head-kidney cells with toll-like receptor ligands induced the expression of typical immune genes (IL1B, CXCL8, TNF, SAA) after only 1 h. The incubation with the stress hormones cortisol, adrenaline and noradrenaline also had an immune-activating effect, though less pronounced. However, cortisol had the strongest suppressive effect on the stimulation-induced immune response, while adrenaline exerted a comparably weaker effect and noradrenaline was almost ineffective. Moreover, we found that cortisol reduced the expression of genes coding for adrenergic and some glucocorticoid receptors, while noradrenaline increased it. In conclusion, the primary head-kidney cells of maraena whitefish reflect the immunological and neuroendocrinological diversity of the entire organ. This in vitro system allowed thus identifying the correlative changes between the activities of hormones and immune factors in salmonid fish in order to contribute to a better understanding of the regulation circuit between stress and immune defence.

Dawn to Dusk: Diurnal Rhythm of the Immune Response in Rainbow Trout (Oncorhynchus Mykiss)

The daily change of light and dark periods influences different physiological processes including feeding, resting and locomotor activity. Previously, several studies on mammalian models revealed a strong link between day-night rhythms and key immunological parameters. Since teleost fishes possess innate and adaptive immune responses like those observed in higher vertebrates, we aimed to elucidate how changes in light-dark cycles shape the immune system of fish. Using the rainbow trout laboratory model, we investigated the link between diurnal rhythms and immune competence of fish. Initially, the cell composition and phagocytic activity of leukocytes was analyzed in the circulation as well as in the head kidney, the functional ortholog of mammalian bone marrow. Once the baseline was established, we evaluated the ability of fish to respond to a bacterial stimulus, as well as the changes in antimicrobial activity of the serum. Our results suggest increased immune competence during the day, manifested by the higher presence of myeloid cells in the circulation; increased overall phagocytic activity; and higher capacity of the sera to inhibit the growth of Aeromonas salmonicida. Notably, our flow cytometric analysis identified the myeloid cells as the major population influenced by the time of day, whereas IgM⁺ B cells and thrombocytes did not vary in a significant manner. Interestingly, the presence of myeloid cells in blood and head kidney followed complementary trends. Thus, while we observed the highest number of myeloid cells in the blood during early morning, we witnessed a reverse trend in the head kidney, suggesting a homing of myeloid cells to reservoir niches with the onset of the dark phase. Further, the presence of myeloid cells was mirrored in the expression of the proinflammatory marker tnfa as well as in the number of leukocytes recruited to the peritoneal cavity in the peritonitis model of inflammation. Overall, the data suggest a connection between diurnal rhythms and the immune response of rainbow trout and highlight the relevance of rhythmicity and its influence on experimental work in the field of fish chronoimmunology.

The Conserved Transcriptional Response to Adversity

Gene expression profiling studies of people exposed to chronic threat have identified a Conserved Transcriptional Response to Adversity (CTRA) in circulating immune cells. This physiological pattern is characterized by up-regulated expression of genes involved in inflammation and down-regulated expression of genes involved in Type I interferon responses. The CTRA is mediated by beta-adrenergic signaling pathways that transduce sympathetic nervous system activity into changes in transcription factor activity and hematopoietic output of myeloid lineage immune cells (monocytes, neutrophils, and dendritic cells). Recent research has begun to identify the CNS processes that regulate peripheral CTRA activity, define its implications for disease, and explore the role of positive psychosocial factors in buffering such effects. The CTRA provides a genomic framework for understanding PNI relationships and connecting macro-level psychosocial processes to the micro-level biology of health and disease.

Gradual and Acute Temperature Rise Induces Crossing Endocrine, Metabolic, and Immunological Pathways in Maraena Whitefish (Coregonus maraena)

The complex and still poorly understood nature of thermoregulation in various fish species complicates the determination of the physiological status on the basis of diagnostic marker genes and indicative molecular pathways. The present study aimed to compare the physiological impacts of both gradual and acute temperature rise from 18 to 24°C on maraena whitefish in aquaculture. Microarray-based transcriptome profiles in the liver, spleen and kidney of heat-stressed maraena whitefish revealed the modulation of a significantly higher number of genes in those groups exposed to gradually rising temperatures compared with the acutely stressed groups, which might reflect early adaptation mechanisms. Moreover, we suggest a common set of 11 differentially expressed genes that indicate thermal stress induced by gradual or acute temperature rise in the three selected tissues. Besides the two pathways regulated in both data sets unfolded protein response and aldosterone signaling in epithelial cells, we identified unique tissue- and stress type-specific pathways reflecting the crossroads between signal transduction, metabolic and immunologic pathways to cope with thermal stress. In addition, comparing lists of differentially regulated genes with meta-analyzed published data sets revealed that “acute temperature rise”-responding genes that encode members of the HSP70, HSP90, and HSP40 families; their functional homologs; co-chaperones and stress-signal transducers are well-conserved across different species, tissues and/or cell types and experimental approaches.

Social genomics of healthy and disordered internet gaming

OBJECTIVES

To combine social genomics with cultural approaches to expand understandings of the somatic health dynamics of online gaming, including in the controversial nosological construct of internet gaming disorder (IGD).

METHODS

In blood samples from 56 U.S. gamers, we examined expression of the conserved transcriptional response to adversity (CTRA), a leukocyte gene expression profile activated by chronic stress. We compared positively engaged and problem gamers, as identified by an ethnographically developed measure, the Positive and Negative Gaming Experiences Scale (PNGE-42), and also by a clinically derived IGD scale (IGDS-SF9).

RESULTS

CTRA profiles showed a clear relationship with PNGE-42, with a substantial linkage to offline social support, but were not meaningfully associated with disordered play as measured by IGDS-SF9.

CONCLUSIONS

Our study advances understanding of the psychobiology of play, demonstrating via novel transcriptomic methods the association of negatively experienced internet play with biological measures of chronic threat, uncertainty, and distress. Our findings are consistent with the view that problematic patterns of online gaming are a proxy for broader patterns of biopsychosocial stress and distress such as loneliness, rather than a psychiatric disorder sui generis, which might exist apart from gamers' other life problems. By confirming the biological correlates of certain patterns of internet gaming, culturally-sensitive genomics approaches such as this can inform both evolutionary theorizing regarding the nature of play, as well as current psychiatric debates about the appropriateness of modeling distressful gaming on substance addiction and problem gambling.

Under control: The innate immunity of fish from the inhibitors' perspective

The innate immune response involves a concerted network of induced gene products, preformed immune effectors, biochemical signalling cascades and specialised cells. However, the multifaceted activation of these defensive measures can derail or overshoot and, if left unchecked, overwhelm the host. A plenty of regulatory devices therefore mediate the fragile equilibrium between pathogen defence and pathophysiological manifestations. Over the past decade in particular, an almost complete set of teleostean sequences orthologous to mammalian immunoregulatory factors has been identified in various fish species, which prove the remarkable conservation of innate immune-control concepts among vertebrates. This review will present the current knowledge on more than 50 teleostean regulatory factors (plus additional fish-specific paralogs) that are of paramount importance for controlling the clotting cascade, the complement system, pattern-recognition pathways and cytokine-signalling networks. A special focus lies on those immunoregulatory features that have emerged as potential biomarker genes in transcriptome-wide research studies. Moreover, we report on the latest progress in elucidating control elements that act directly with immune-gene-encoding nucleic acids, such as transcription factors, hormone receptors and micro- and long noncoding RNAs. Investigations into the function of teleostean inhibitory factors are still mainly based on gene-expression profiling or overexpression studies. However, in support of structural and in-vitro analyses, evidence from in-vivo trials is also available and revealed many biochemical details on piscine immune regulation. The presence of multiple gene copies in fish adds a degree of complexity, as it is so far hardly understood if they might play distinct roles during inflammation. The present review addresses this and other open questions that should be tackled by fish immunologists in future.

Chronic stress inhibits growth and induces proteolytic mechanisms through two different nonoverlapping pathways in the skeletal muscle of a teleost fish

Chronic stress detrimentally affects animal health and homeostasis, with somatic growth, and thus skeletal muscle, being particularly affected. A detailed understanding of the underlying endocrine and molecular mechanisms of how chronic stress affects skeletal muscle growth remains lacking. To address this issue, the present study assessed primary (plasma cortisol), secondary (key components of the GH/IGF system, muscular proteolytic pathways, and apoptosis), and tertiary (growth performance) stress responses in fine flounder ( Paralichthys adspersus) exposed to crowding chronic stress. Levels of plasma cortisol, glucocorticoid receptor 2 ( gr2), and its target genes ( klf15 and redd1) mRNA increased significantly only at 4 wk of crowding ( P < 0.05). The components of the GH/IGF system, including ligands, receptors, and their signaling pathways, were significantly downregulated at 7 wk of crowding ( P < 0.05). Interestingly, chronic stress upregulated the ubiquitin-proteasome pathway and the intrinsic apoptosis pathways at 4wk ( P < 0.01), whereas autophagy was only significantly activated at 7 wk ( P < 0.05), and meanwhile the ubiquitin-proteasome and the apoptosis pathways returned to control levels. Overall growth was inhibited in fish in the 7-wk chronic stress trial ( P < 0.05). In conclusion, chronic stress directly affects muscle growth and downregulates the GH/IGF system, an action through which muscular catabolic mechanisms are promoted by two different and nonoverlapping proteolytic pathways. These findings provide new information on molecular mechanisms involved in the negative effects that chronic stress has on muscle anabolic/catabolic signaling balance.