Are hsps suitable for indicating stressed states in fish?

Molecular characterization of Lernathropus kroyeri from intensive aquaculture and pathophysiology of infested sea bass

The copepod Lernathropus kroyeri constitutes one of the major parasites for the Mediterranean aquaculture, infesting the sea bass Dicentrarchus labrax causing thus disruptions of growth performance and occasionally mortalities. Despite the large spread and the high frequency of this parasite in mariculture farms of Eastern Mediterranean, L. kroyeri genetic profile from aquaculture as well as the pathophysiological response of D. labrax have not been studied so far. Keeping this in mind, in the present study we investigated the L. kroyeri infestation on D. labrax from two farms in Greece, examining both healthy and heavy parasitized individuals. Assays included histopathology, phylogenetic reconstruction of the parasite and physiological response of the fish by the means of antioxidant, inflammatory metabolic and stress related gene expression analysis at both mRNA and protein levels. Genetic analysis indicated that L. kroyeri composes a monophyletic group, highly phylogenetically distant from other congeneric groups. Heavy infested D. labrax witnessed a significantly increased immune response that further led to oxidative stress and metabolic alterations. Overall, our results demonstrate the, seasonally independent, high infestation of this parasitic copepods, which continue to affect Mediterranean intensive aquaculture systems.

Toxicogenomic Effects of Dissolved Saxitoxin on the Early Life Stages of the Longfin Yellowtail (Seriola rivoliana)

Harmful algal blooms (HABs) can produce a variety of noxious effects and, in some cases, the massive mortality of wild and farmed marine organisms. Some HAB species produce toxins that are released into seawater or transferred via food webs (particulate toxin fraction). The objective of the present study was to identify the toxicological effects of subacute exposure to saxitoxin (STX) during embryonic and early larval stages in Seriola rivoliana. Eggs were exposed to dissolved 19 STX (100 μg L-1). The toxic effects of STX were evaluated via the hatching percentage, the activity of three enzymes (protein and alkaline phosphatases and peroxidase), and the expression of four genes (HSF2, Nav1.4b, PPRC1, and DUSP8). A low hatching percentage (less than 5%) was observed in 44 hpf (hours post fertilization) embryos exposed to STX compared to 71% in the unexposed control. At this STX concentration, no oxidative stress in the embryos was evident. However, STX induced the expression of the NaV1.4 channel α-subunit (NaV1.4b), which is the primary target of this toxin. Our results revealed the overexpression of all four candidate genes in STX-intoxicated lecithotrophic larvae, reflecting the activation of diverse cellular processes involved in stress responses (HSF2), lipid metabolism (PPRC1), and MAP kinase signaling pathways associated with cell proliferation and differentiation (DUSP8). The effects of STX were more pronounced in young larvae than in embryos, indicating a stage-specific sensitivity to the toxin.

Transcriptomic analyses of juvenile Striped Bass (Morone saxatilis) exposed to chronic and acute temperature change

Striped Bass are economically important, migratory fishes, which occur across a wide range of latitudes. Given their wide-ranging nature, Striped Bass can cope with a broad range of environmental temperatures, yet the mechanisms underlying this ability have not been thoroughly described. Heat shock proteins (HSPs) are inducible molecular chaperones, which help mitigate protein damage resulting from increased temperatures. The importance of HSPs has been demonstrated in a number of fish species, but their role in Striped Bass is poorly understood. This study characterizes changes in gene expression in juvenile Striped Bass, following acute and chronic temperature change. Fish were acclimated to one of three temperatures (15, 25 or 30°C) and sampled at one of two treatments (control or after CTmax), following which we assessed differential gene expression and gene ontology in muscle. It is clear from our differential expression analyses that acclimation to warm temperatures elicits more robust changes to gene expression, compared to acute temperature increases. Our differential expression analyses also revealed induction of many different heat shock proteins, including hsp70, hsp90, hsp40 and other small HSPs, after both acute and chronic temperature increase in white muscle. Furthermore, the most consistent gene ontology pattern that emerged following both acclimation and CTmax was upregulation of transcripts involved in "protein folding", which also include heat shock proteins. Gene ontology analyses also suggest changes to other processes after acclimation, including decreased growth pathways and changes to DNA methylation. Overall, these data suggest that HSPs likely play a major role in the Striped Bass's ability to tolerate warm waters.

Heat induces multiomic and phenotypic stress propagation in zebrafish embryos

Heat alters biology from molecular to ecological levels, but may also have unknown indirect effects. This includes the concept that animals exposed to abiotic stress can induce stress in naive receivers. Here, we provide a comprehensive picture of the molecular signatures of this process, by integrating multiomic and phenotypic data. In individual zebrafish embryos, repeated heat peaks elicited both a molecular response and a burst of accelerated growth followed by a growth slowdown in concert with reduced responses to novel stimuli. Metabolomes of the media of heat treated vs. untreated embryos revealed candidate stress metabolites including sulfur-containing compounds and lipids. These stress metabolites elicited transcriptomic changes in naive receivers related to immune response, extracellular signaling, glycosaminoglycan/keratan sulfate, and lipid metabolism. Consequently, non-heat-exposed receivers (exposed to stress metabolites only) experienced accelerated catch-up growth in concert with reduced swimming performance. The combination of heat and stress metabolites accelerated development the most, mediated by apelin signaling. Our results prove the concept of indirect heat-induced stress propagation toward naive receivers, inducing phenotypes comparable with those resulting from direct heat exposure, but utilizing distinct molecular pathways. Group-exposing a nonlaboratory zebrafish line, we independently confirm that the glycosaminoglycan biosynthesis-related gene chs1 and the mucus glycoprotein gene prg4a, functionally connected to the candidate stress metabolite classes sugars and phosphocholine, are differentially expressed in receivers. This hints at the production of Schreckstoff-like cues in receivers, leading to further stress propagation within groups, which may have ecological and animal welfare implications for aquatic populations in a changing climate.

Sub-chronic ammonia exposure induces hepatopancreatic damage, oxidative stress, and immune dysfunction in red swamp crayfish (Procambarus clarkii)

Ammonia, as one of the primary water pollutants in aquaculture, has been shown to induce a wide range of ecotoxicological effects on aquatic animals. In order to investigate the antioxidant and innate immune responses in crustaceans disrupted by ammonia, red swamp crayfish (Procambarus clarkii) were exposed to 0, 15, 30, and 50 mg/L total ammonia nitrogen for 30 d, the alterations of antioxidant responses as well as innate immunity were studied. The results showed that the severity of hepatopancreatic injury were aggravated by the increasing ammonia levels, which were mainly characterized by tubule lumen dilatation and vacuolization. The swollen mitochondria and disappeared mitochondria ridges suggested that oxidative stress induced by ammonia targets the mitochondria. Concurrently, enhanced MDA levels, and decreased GSH levels as well as the decreased transcription and activity of antioxidant enzymes, including SOD, CAT, and GPx were noticed, which suggested that high concentrations of ammonia exposure induce oxidative stress in P. clarkii. Furthermore, a significant decrease of the hemolymph ACP, AKP, and PO along with the significant downregulation of immune-related genes (ppo, hsp70, hsp90, alf1, ctl) jointly indicated that ammonia stress inhibited the innate immune function. Our findings demonstrated that sub-chronic ammonia stress induced hepatopancreatic injury and exert suppressive effects on the antioxidant capacity as well as innate immunity of P. clarkii. Our results provide a fundamental basis for the deleterious effects of ammonia stress on aquatic crustaceans.

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

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

Impact of nitrite exposure on oxidative stress and antioxidative-related genes responses in the gills of Procambarus clarkii

Nitrite is the major environmental pollutant in the freshwater aquaculture environment, which has a negative impact on aquatic species growth. Currently, we know that the main way nitrite enters crustaceans is through their gills. In this study, a total of 96 h acute nitrite stress (60 mg/L) experiments were conducted, and the impact of the serum biochemical parameters, gill oxidase activity and oxidative-related gene expression of red swamp crayfish were evaluated. After exposure to nitrite for 0, 6, 12, 24, 48, and 96 h, hemolymph and gills samples were taken at each time point. In the serum, acute nitrite stress significantly increased glutamic-oxaloacetic transaminase (GOT) and alanine aminotransferase (ALT) activities after 6 h of exposure, decreased total protein (TP) and albumin (ALB) levels after 24 h and 48 h of exposure, respectively. In the gills, the activities of catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were enhanced to the maximum level at 12 h, 24 h and 24 h, respectively. The contents of malondialdehyde (MDA) and lipid peroxide (LPO) were increased significantly after 12 h and 24 h exposure, respectively. In addition, the expression levels of antioxidative-related genes, including hsp70, fer and mt, were significantly upregulated in the gills after 6 h of exposure. The results indicated that acute nitrite stress changed the serum physiological status, induced oxidative stress and caused damage to gill cells in P. clarkii.

Anesthetic and sedative efficacy of essential oil of Hesperozygis ringens and the physiological responses of Oreochromis niloticus after biometric handling and simulated transport

This study aimed to evaluate different concentrations of the essential oil of Hesperozygis ringens (EOHR) and its effects on anesthesia and transport of Oreochromis niloticus. Experiment I evaluated the concentrations of 0, 150, 300, 450, and 600 µL L^-1 EOHR for times of induction and recovery from anesthesia and ventilatory frequency (VF) of O. niloticus (26 g), with 10 repetitions each in a completely randomized design. Based on the results of Experiment I, Experiment II submitted fish (25 g) to three treatments-control (clean water), ethanol (5 mL ethyl alcohol), and 600 µL L^-1 EOHR-and then handling for biometry. Blood was collected 1 and 24 h after exposure and handling to analyze hematological and biochemical parameters in a completely randomized design in a factorial arrangement (3 × 2). Experiment III submitted fish (35 g) to simulated transport (4.5 h) with 0, 10, or 20 µL L^-1 EOHR and determined the effects on blood variables. Concentrations of 450 and 600 µL L^-1 EOHR provoked deep anesthesia in juvenile O. niloticus and provided induction and recovery times within the limits considered ideal for fish. However, this essential oil was not able to attenuate the effects of stress caused by biometric handling. EOHR was able to attenuate the effects of stress from simulated transport, with 10 µL L^-1 EOHR being responsible for causing a decrease in protein, triglycerides, and cholesterol values immediately after transport of O. niloticus.

Tenets in Microbial Endocrinology: A New Vista in Teleost Reproduction

Climate vulnerability and induced changes in physico-chemical properties of aquatic environment can bring impairment in metabolism, physiology and reproduction in teleost. Variation in environmental stimuli mainly acts on reproduction by interfering with steroidogenesis, gametogenesis and embryogenesis. The control on reproductive function in captivity is essential for the sustainability of aquaculture production. There are more than 3,000 teleost species across the globe having commercial importance; however, adequate quality and quantity of seed production have been the biggest bottleneck. Probiotics are widely used in aquaculture as a growth promoter, stress tolerance, pathogen inhibition, nutrient digestibility and metabolism, reproductive performance and gamete quality. As the gut microbiota exerts various effects on the intestinal milieu which influences distant organs and pathways, therefore it is considered to be a full-fledged endocrine organ. Researches on Gut-Brain-Gonad axis (GBG axis) and its importance on physiology and reproduction have already been highlighted for higher mammals; however, the study on fish physiology and reproduction is limited. While looking into the paucity of information, we have attempted to review the present status of microbiome and its interaction between the brain and gut. This review will address a process of the microbiome physiological mechanism involved in fish reproduction. The gut microbiota influences the BPG axis through a wide variety of compounds, including neuropeptides, neurotransmitter homologs and transmitters. Currently, research is being conducted to determine the precise process by which gut microbial composition influences brain function in fish. The gut-brain bidirectional interaction can influence brain biochemistry such as GABA, serotonin and tryptophan metabolites which play significant roles in CNS regulation. This review summarizes the fact, how microbes from gut, skin and other parts of the body influence fish reproduction through the Gut-Brain-Gonad axis.

Multi-biomarker approach to assess chromium, pH and temperature toxicity in fish

Chromium (Cr) is considered as the most common ubiquitous pollutant for aquatic animals including fish. An experiment was conducted to determine the acute and chronic toxicity of Cr, pH and high temperature in Anabas testudineus. Lethal concentration (LC₅₀) of Cr alone was determined as 55.02 mg L^-1, Cr and low pH 48.19 mg L^-1 and Cr, low pH and high temperature 47.16 mg L^-1. The chronic toxicity of low dose of Cr, pH and high temperature (1/10th and 1/20th of LC₅₀) was designed to execute the experiment for 72 days. The stress enzymes and biomarkers were determined viz. superoxide dismutase, catalase, glutathione peroxidase, glutathione-s-transferase, lipid peroxide, acetylcholine esterase, cortisol, HSP-70, blood glucose, aspartate amino transferase, alanine amino transferase and malate dehydrogenase, lactate dehydrogenase, ATPase and genotoxicity in this study. We had also studied the integrated biomarker response (IBR), which revealed that Cr toxicity enhanced with concurrent exposure to pH and high temperature. All the biochemical attributes were significantly altered with exposure to Cr alone and with low pH and high temperature except gill SOD. Further, thermal tolerance was also determined, and results revealed that thermal tolerance was significantly reduced with exposure to Cr alone and Cr and low pH exposure in A. testudineus. The present study concluded that, the chronic toxicity of Cr is enhanced with low pH and high temperature and it has led to understanding the multi-approach of Cr toxicity which affect, stress biomarkers, cellular metabolic stress and thermal tolerance of A. testudineus.

Towards the integration of ecophysiology with fisheries stock assessment for conservation policy and evaluating the status of the Mediterranean Sea

Recent European Union (EU) regulations have been introduced to discourage the capture of undersized specimens with the aim of reducing the bycatch mortality imposed by commercial fisheries. We argue that we still lack accurate data regarding basic information required to properly implement these regulations for most Mediterranean ecosystems, including the true mortality imposed by fisheries, escape rates from fishing gears and the capability of specimens to survive following discard. We suggest that additional reliance on physiological biomarkers could assist in all aspects of the data collection required to support implementation of the EU discard ban (aka landing obligation), particularly in determining which species should receive special dispensation from this policy. Ideally, this new approach, here termed the 'Fisheries Environmental and Physiological Stress Analysis' (FEPSA), would become an important step for any fish stock assessment within the ecosystem approach to fisheries management and the recognition of Good Environmental Status, as established by the EU in the Marine Strategy Framework Directive (2008/56/EC). In particular, the main goal of FEPSA would be applying the study of physiological stressors to exploited stocks to estimate the so-called collateral fishing mortality, which includes the mortality experienced by fish that escape after interacting with fishing gears or that are discarded, with some degree of injury or physiological stress. The approach outlined here, which is described for bottom trawls but adaptable to any other type of fishing gear, is not a trivial undertaking but is a requirement for collecting the data required by recent EU fisheries policies. While we agree that the threats to marine biodiversity posed by fishing and associated discard practices require strong policy interventions, we emphasize that the research programs needed to support such initiatives, including the landing obligation, should be given equal priority. This is particularly true for Mediterranean fisheries, which are at a complex intersection of jurisdictional boundaries, numerous additional ecosystem threats including widespread pollution, thermal variation and hypoxia, and are historically understudied as compared to fisheries and species in more northern climates.

RNA-seq Analysis Reveals Alternative Splicing Under Heat Stress in Rainbow Trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) is one of the most economically important cold-water farmed species in the world, and transcriptomic studies in response to heat stress have been conducted and will be studied in depth. Alternative splicing (AS), a post-transcriptional regulatory process that regulates gene expression and increases proteomic diversity, is still poorly understood in rainbow trout under heat stress. In the present study, 18,623 alternative splicing events were identified from 9936 genes using RNA transcriptome sequencing technology (RNA-Seq) and genomic information. A total of 2731 differential alternative splicing (DAS) events were found among 2179 differentially expressed genes (DEGs). Gene ontology analysis revealed that the DEGs were mainly enriched in cellular metabolic process, cell part, and organic cyclic compound binding under heat stress. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis displayed that the DEGs were enriched for 39 pathways, and some key pathways, such as lysine degradation, are involved in the regulation of heat stress in liver tissues of rainbow trout. The results were validated by qRT-PCR, confirming reliability of our bioinformatics analysis.

Intermittent administration of peracetic acid is a mild environmental stressor that elicits mucosal and systemic adaptive responses from Atlantic salmon post-smolts

Background

Fish encounter oxidative stress several times during their lifetime, and it has a pervasive influence on their health and welfare. One of the triggers of oxidative stress in fish farming is the use of oxidative disinfectants to improve rearing conditions, especially in production systems employing recirculation technology. Here we report the physiological and morphological adaptive responses of Atlantic salmon (Salmo salar L.) post-smolts to intermittent exposure to a potent oxidative agent peracetic acid (PAA). Fish reared in semi-commercial scale brackish water recirculating aquaculture system (RAS) were exposed to 1 ppm PAA every 3 days over 6 weeks. Mucosal and systemic responses were profiled before exposure, 22 and 45 days during the intermittent PAA administration.

Results

Oxidative stress was likely triggered as plasma antioxidant capacity increased significantly during the exposure period. Adaptive stress response to the periodic oxidant challenge was likewise demonstrated in the changes in plasma glucose and lactate levels. PAA-induced alterations in the transcription of antioxidants, cytokines, heat shock proteins and mucin genes showed a tissue-specific pattern: downregulation was observed in the gills and olfactory rosette, upregulation occurred in the skin, and no substantial changes in the liver. Further, PAA exposure resulted in histological changes in key mucosal organs (i.e. olfactory rosette, skin and gills); pathological alterations were predominant in the gills where cases of epithelial lifting, hypertrophy and clubbing were prevalent. In addition, intermittent PAA administration resulted in an apparent overproduction of mucus in the nasal mucosa. Lastly, PAA did not dramatically alter the ability of salmon to mount a physiological stress response in the presence of a secondary stressor, though some subtle interference was documented in the kinetics and magnitude of plasma cortisol and glucose response post-stress.

Conclusions

The present study collectively demonstrated that intermittent oxidant exposure was a mild environmental stressor that salmon could mount strong adaptive responses at systemic and mucosal levels. The results will be valuable in optimising the rearing conditions of post-smolts in RAS, especially in adopting water treatment strategies that do not considerably interfere with fish health and welfare.

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

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

Large within, and between, species differences in marine cellular responses: Unpredictability in a changing environment

Predicting the impacts of altered environments on future biodiversity requires a detailed understanding of organism responses to change. To date, studies evaluating mechanisms underlying marine organism stress responses have largely concentrated on oxygen limitation and the use of heat shock proteins as biomarkers. However, whether these biomarkers represent responses that are consistent across species and different environmental stressors remains open to question. Here we show that responses to four different thermal stresses (three rates of thermal ramping (1 °C h^-1, 1 °C day^-1 or 1 °C 3 day^-1) and a three-month acclimation to warming of 2 °C) applied to three species of Antarctic marine invertebrate produced highly individual responses in gene expression profiles, both within and between species. Mapping the gene expression profiles from each treatment for each of the three species, identified considerable difference in numbers of differentially regulated transcripts ranging from 10 to 3011. When these data were correlated across the different temperature treatments, there was no evidence for a common response with only 0-2 transcripts shared between all four treatments within any one species. There were also no shared differentially expressed genes across species, even at the same thermal ramping rates. The classical cellular stress response (CSR) i.e. up-regulation of heat shock proteins, was only strongly present in two species at the fastest ramping rate of 1 °C h^-1, albeit with different sets of stress genes expressed in each species. These data demonstrate the wide variability in response to warming at the molecular level in marine species. Therefore, identification of biodiversity stress responses engendered by changing conditions will require evaluation at the species level using targeted key members of the ecosystem, strongly correlated to the local biotic and abiotic factors.

Carbofuran affects behavior and metabolism of the Atlantic Forest lambari Deuterodon iguape, a native species from Brazil

One of the major causes of aquatic biodiversity loss is the contamination of the environment by pesticides. Even though there is a considerable amount of studies on the subject, there are still few that deal with the effects of carbofuran on native species in Brazil. Although carbofuran is widely used in Brazil, its action on native organisms, such as the Atlantic Forest lambari Deuterodon iguape, has not yet been studied. This work aimed to evaluate the effects of exposure to carbofuran on the fish D. iguape, considering the behavior and specific oxygen consumption as end points. Opercular movements, dorsal fin movements, and swimming speed were analyzed as behavioral parameters. To assess specific oxygen consumption, fish were subjected to concentrations of 0.0, 0.05, 0.1, 0.25, and 0.5 mg/L, for 24 h. For behavior analysis, fish remained exposed to carbofuran at concentrations of 0.0, 0.01, 0.05, 0.1, and 0.5 mg/L, in periods of 0, 2, 24, and 48 h. The behavior was studied through filming, analyzed with the free software, Tracker 4.92 (Open Source Physics). The results demonstrate an increase in opercular movements (18% ± 2.65) and a decrease in dorsal fin movements (- 21.2% ± 2.97), as well as in swimming speed (- 58.3% ± 1.83) of the experimental groups compared to the control group. There was an increase in oxygen consumption of 58.4% in fish exposed to the highest concentration of carbofuran. Thus, it is concluded that carbofuran altered D. iguape's behavior and oxygen consumption. The species was sensitive to carbofuran concentrations and can be used as a bioindicator.

Oxytocin Signaling Acts as a Marker for Environmental Stressors in Zebrafish

The oxytocin system plays a role in stress responses and behavior modulation. However, the effects of oxytocin signaling on stress adaptation remain unclear. Here, we demonstrated the roles of oxytocin signaling as a biomarker under stress conditions in the peripheral tissues (the gills) and central nervous system (the brain). All the environmental stressors downregulated the expression of oxytocin receptors in the gills, and the alteration of the expression of oxytocin receptors was also found in the brain after the acidic (AC) and high-ammonia (HA) treatments. The number of oxytocin neurons was increased after double-deionized (DI) treatment. By transgenic line, Tg(oxtl:EGFP), we also investigated the projections of oxytocin neurons and found oxytocin axon innervations in various nuclei that might regulate the anxiety levels and aggressiveness of adult zebrafish under different environmental stresses. The oxytocin system integrates physiological responses and behavioral outcomes to ensure environmental adaptation in adult zebrafish. Our study provides insight into oxytocin signaling as a stress indicator upon environmental stressors.

Global warming overrides physiological anti-predatory mechanisms in intertidal rock pool fish Gobius paganellus

In nature, a multitude of factors influences the fitness of an organism at a given time, which makes single stressor assessments far from ecologically relevant scenarios. This study focused on the effects of water temperature and predation stress on the metabolism and body mass gain of a common intertidal rock pool fish, Gobius paganellus, addressing the following hypotheses: (1) the energy metabolism of G. paganellus under predation stress is reduced; (2) G. paganellus shows thermal compensation under heat stress; and (3) thermal stress is the dominant stressor that may override predation stress responses. Individuals were exposed to simulated predation stress and temperature increase from 20 °C to 29 °C, and both stressors combined. Physiological effects were addressed using biochemical biomarkers related with energy metabolism (isocitrate dehydrogenase, lactate dehydrogenase, energy available, energy consumption rates), oxidative stress (superoxide dismutase, catalase, DNA damage, lipid peroxidation), and biotransformation (glutathione-S-transferase). The results of this study revealed that predation stress reduced the cellular metabolism of G. paganellus, and enhanced storage of protein reserves. As hypothesized, hyperthermia decreased the aerobic mitochondrial metabolism, indicating thermal compensation mechanisms to resist against unfavourable temperatures. Hyperthermia was the dominant stressor overriding the physiological responses to predation stress. Both stressors combined might further have synergistically activated detoxification pathways, even though not strong enough to counteract lipid peroxidation and DNA damage completely. The synergistic effect of combined thermal and predation stress thus may not only increase the risk of being preyed upon, but also may indicate extra energy trade-off for the basal metabolism, which in turn may have ecologically relevant consequences for general body functions such as somatic growth and reproduction. The present findings clearly underline the ecological importance of multi-stressor assessments to provide a better and holistic picture of physiological responses towards more realistic evaluations of climate change consequences for intertidal populations.

The environmental context of inducible HSP70 expression in Eastern Brook Trout

Much research has focused on the population-level effects of climate change on Eastern Brook Trout (Salvelinus fontinalis). While some studies have considered here sub-lethal stress caused by warming waters, the role of multiple, interacting stressors remains largely unexplored. We used inducible heat shock protein 70 (HSP70) as a molecular biomarker to assess in situ response of Eastern Brook Trout in headwater streams to multiple potential stressors, including temperature. Over 7 sampling events during 2018 and 2019, we sampled 141 fish and found that HSP70 expression and 3-day mean water temperature exhibited a quadratic relationship (R ²-adj = 0.68). Further analyses showed that HSP70 expression was explained by temperature, relative water level and their interaction (R ²-adj = 0.75), while fish size and capture location were not factors. We observed a significant increase in HSP70 expression during periods of low relative water level with warm temperatures (~18°C) and also during high relative water level with cold temperatures (~8°C). Our results suggest that temperatures at the edges of the preferred range coupled with relative water level might act together to trigger the cellular stress response in Eastern Brook Trout and that there is greater variation in response at colder temperatures. These findings reinforce the need to consider complex, interactive stressors in influencing the health and persistence of Eastern Brook Trout populations into the future.

Effect of temperature on food consumption, immune system, antioxidant enzymes, and heat shock protein 70 of Channa punctata (Bloch, 1793)

The impact of water temperature on the physiology of Channa punctata (Bloch, 1793) was evaluated in the present study. Fish were acclimated at 25 ± 1 °C and then exposed at six different temperatures: 10, 15, 20, 25, 30, and 35 °C. C. punctata exposed at 10, 15, and 20 °C showed 30, 21, and 11% reduced food consumption, respectively compared to 25 °C. Significantly higher respiratory burst and myeloperoxidase activities were found in fish exposed at 20 and 25 °C after 12 h of exposure compared to other treatments. Nitric oxide synthase was significantly higher at 25 °C after 12 h and at 25 and 30 °C exposed fish after 7 days compared to others. The reduced glutathione level was significantly higher at 25 °C compared to other treatments after 7 days of exposure. The thiobarbituric acid reactive substances level was minimum at 25 °C. Significantly lower antioxidant enzymes, catalase, glutathione peroxidase, and glutathione S-transferase were found in gills of fish exposed at 25 °C compared to others in both samples. The highest antioxidant enzyme levels were found at 10 °C. Heat shock protein (Hsp) 70 levels were significantly lower in liver and muscle of fish exposed at 25 °C compared to other treatments. The Hsp level was significantly higher at 35 and 30 °C exposed fish compared to others after 12 h, and the level reduced after 7 days in these treatments. Thermal stress affects food consumption rate, immune system, antioxidant enzymes, and enzyme systems in fish. The elevated Hsp70 level serves as a biomarker of stress in C. punctata. Graphical Abstract.

Effects of acclimation temperature on the thermal physiology in two geographically distinct populations of lake sturgeon (Acipenser fulvescens)

Temperature is one of the most important abiotic factors regulating development and biological processes in ectotherms. By 2050, climate change may result in temperature increases of 2.1-3.4°C in Manitoba, Canada. Lake sturgeon, Acipenser fulvescens, from both northern and southern populations in Manitoba were acclimated to 16, 20 and 24°C for 30 days, after which critical thermal maximum (CT_max) trials were conducted to investigate their thermal plasticity. We also examined the effects of temperature on morphological and physiological indices. Acclimation temperature significantly influenced the CT_max, body mass, hepatosomatic index, metabolic rate and the mRNA expression of transcripts involved in the cellular response to heat shock and hypoxia (HSP70, HSP90a, HSP90b, HIF-1α) in the gill of lake sturgeon. Population significantly affected the above phenotypes, as well as the mRNA expression of Na⁺/K⁺ ATPase-α1 and the hepatic glutathione peroxidase enzyme activity. The southern population had an average CT_max that was 0.71 and 0.45°C higher than the northern population at 20 and 24°C, respectively. Immediately following CT_max trials, mRNA expression of HSP90a and HIF-1α was positively correlated with individual CT_max of lake sturgeon across acclimation treatments and populations (r = 0.7, r = 0.62, respectively; P < 0.0001). Lake sturgeon acclimated to 20 and 24°C had decreased hepatosomatic indices (93 and 244% reduction, respectively; P < 0.0001) and metabolic suppression (27.7 and 42.1% reduction, respectively; P < 0.05) when compared to sturgeon acclimated to 16°C, regardless of population. Glutathione peroxidase activity and mRNA expression Na⁺/K⁺ ATPase-α1 were elevated in the northern relative to the southern population. Acclimation to 24°C also induced mortality in both populations when compared to sturgeon acclimated to 16 and 20°C. Thus, increased temperatures have wide-ranging population-specific physiological consequences for lake sturgeon across biological levels of organization.

Comparative transcriptomics reveal conserved impacts of rearing density on immune response of two important aquaculture species

Infectious diseases represent an important barrier to sustainable aquaculture development. Rearing density can substantially impact fish productivity, health and welfare in aquaculture, including growth rates, behaviour and, crucially, immune activity. Given the current emphasis on aquaculture diversification, stress-related indicators broadly applicable across species are needed. Utilising an interspecific comparative transcriptomic (RNAseq) approach, we compared gill gene expression responses of Atlantic salmon (Salmo salar) and Nile tilapia (Oreochromis niloticus) to rearing density and Saprolegnia parasitica infection. Salmon reared at high-density showed increased expression of stress-related markers (e.g. c-fos and hsp70), and downregulation of innate immune genes. Upon pathogen challenge, only salmon reared at low density exhibited increased expression of inflammatory interleukins and lymphocyte-related genes. Tilapia immunity, in contrast, was impaired at low-density. Using overlapping gene ontology enrichment and gene ortholog analyses, we found that density-related stress similarly impacted salmon and tilapia in key immune pathways, altering the expression of genes vital to inflammatory and Th₁₇ responses to pathogen challenge. Given the challenges posed by ectoparasites and gill diseases in fish farms, this study underscores the importance of optimal rearing densities for immunocompetence, particularly for mucosal immunity. Our comparative transcriptomics analyses identified density stress impacted immune markers common across different fish taxa, providing key molecular targets with potential for monitoring and enhancing aquaculture resilience in a wide range of farmed species.

Effects of reducing dietary fishmeal with yeast supplementations on Litopenaeus vannamei growth, immune response and disease resistance against Vibrio harveyi

The aim of this experiment was to investigate the effects of reducing dietary fishmeal (FM) with yeast culture (SYC) supplementation on growth, immune response, intestinal microbiota, intestinal morphology, and disease resistance of Litopenaeus vannamei. A total of 480 shrimps with an average initial body weight of 0.35 ± 0.002 g were randomly distributed into twelve tanks. Three isonitrogenous (40.00 crude protein) and isolipidic (8.00 crude lipids) diets with yeast culture supplementing fishmeal were formulated. The groups were divided into two (2) namely control group and experimental groups. The formulations of the groups were control (0 %, without yeast culture) and the experiment groups (SYC) [(1 % of yeast culture), and (2 % of yeast culture)]. Each diet was delivered in four replicate per treatment group. The results indicate significant improvement on the growth indices (specific growth rate, weight gain rate, survival rate and lower feed conversion ratio) with yeast culture treatment group after 56 days feeding trials (P < 0.05). Total hemolymph protein, superoxide dismutase, catalase, alkaline phosphatase, acid phosphatase, lysozyme and phenoxidase were enhanced but low aspartate aminotransferase, alanine aminotransferase, and glucose were observed in shrimp fed yeast culture diets (P < 0.05). The SYC groups showed insignificant differences in hemolymph cholesterol and triglyceride. Proteobacteria, Bacteroidetes, and Actinobacteria were the dominant bacteria found in all the SYC groups. At the genus level, Vibrio was significantly decreased (P < 0.05) in 2 % yeast culture diets supplemented group whereas the beneficial bacteria Pseudoalteromonas was significantly enhanced. Moreover, intestinal villus length and width in shrimps fed yeast culture diets were improved (P < 0.05). Dietary yeast culture supplementation can improve growth, intestinal health, immune response, and resistance against Vibrio harveyi infections in L. vannamei.

Transcriptomic responses to pollution in natural riverine environment in Rita rita

Aquatic pollution is one of the most common threats to the ecological health of aquatic ecosystems and its biota. Fish as lower vertebrates are excellent model to study the impact and responses of aquatic pollution. In fish, gill is the main organ indicator of whole animal health as it comes in contact with the surrounding water and absorbs many pollutants and contaminants; therefore, investigations on alterations in fish gill at transcriptome level could provide newer insights to the stress response mechanism(s) and pathways. For comprehensive evaluation of the impacts of pollutants (joint toxicity) prevalent in the riverine environment, comparative transcriptome analysis, by Next Generation Sequencing under Illumina HiSeq 2500 platform, was carried out in gill tissues of Rita rita collected from two stretches of river Ganga (Kanpur and Farakka) and results were validated by RT-qPCR. Out of 154,077 unigenes (Accession SRR548008), a total of 2024 differentially expressed genes (DEGs) including 942 up-regulated and 1082 down-regulated genes were identified by DESeq program. Further, Gene Ontology (GO) of DEGs showed that ribosomal large subunit biogenesis, mitochondrial ribosome and box H/ACA SnoRNA binding categories are highly affected by pollution. Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway analysis showed the involvement of the DEGs in energy metabolism, translational and transcriptional machinery, protein folding and degradation suggesting that these signalling pathways are highly affected by aquatic pollution. Among the DEGs, up-regulation of cytochrome c oxidase subunit (cox) 7a2 (69.47 fold), hsp70 subunit 14 (hsp70-14, 5.27 fold), muscle related coiled-coil protein (MURC, 21.55 fold), lysozyme G (40.14 fold), cox17 (29.36 fold) were the conspicuous ones which showed similar trends in expression when analysed by RT-qPCR. Based on fold change, perturbation values, correlation analysis by PCA and RT-qPCR validation, up-regulation of cox7a2, MURC and hsp70-14 appeared to be the most promising biomarker responses and could be useful in the evaluation of gill health and possibly be extended towards aquatic ecosystem health assessment.

Potential osmoprotective roles of branchial heat shock proteins towards Na+, K+-ATPase in milkfish (Chanos chanos) exposed to hypotonic stress

In euryhaline teleosts, osmoregulatory mechanisms vary with osmotic stresses, and heat shock proteins (HSPs) play a central role in maintaining cellular homeostasis. The present study aimed to investigate the expression and potential roles of HSP70 and HSP90 in the gills of seawater (SW)- and freshwater (FW)-acclimated milkfish (Chanos chanos). Four HSP genes, including Cchsc70 (heat shock cognate 70), Cchsp70, Cchsp90α, and Cchsp90β, were analyzed in milkfish gills. Among these genes, only the mRNA abundance of branchial Cchsp90α was significantly lower in the FW-acclimated than in the SW-acclimated milkfish. Immunoblotting showed no significant difference in the relative protein abundance of branchial HSP70 and HSP90 between the two groups. The time-course experiments (from SW to FW) showed that the protein abundance of HSP70 and HSP90 at the 3 h and 6 h post-transfer and then declined gradually. To further illustrate the potential osmoregulatory roles of HSP70 and HSP90, their interaction with Na⁺, K⁺-ATPase (NKA, the primary driving force for osmoregulation) was analyzed using co-immunoprecipitation. The results showed the interaction between HSP70, HSP90 and NKA after acclimation to SW or FW increased within 3 h; and then returned to normal levels within 7 days. To our knowledge, the present study was the first to demonstrate that the interaction between HSP70, HSP90 and NKA changes with hypotonic stress in euryhaline teleosts. Before the transfer, no interaction was detected. When transferred to FW from SW, the interaction of HSP70 and HSP90 with NKA were detected. The results suggested that HSP70 and HSP90 participated in the acute responses of osmoregulatory mechanisms to protect branchial NKA from hypotonic stress in milkfish.

Resting time before slaughter restores homeostasis, increases rigor mortis time and fillet quality of surubim Pseudoplatystoma spp

This study assesses the respiratory dynamics related to stress parameters and resting time before slaughter, in the quality of surubim (Pseudopatystoma spp.) fillets. A completely randomized design was conducted using five treatments: resting time before slaughter of 0, 2, 4, 8 and 24 hours, with 15 fish sampled per treatment. Time 0 corresponded to the treatment without resting time, where the fish were slaughtered immediately after arriving at the processing plant. The resting time did not affect the electrolyte balance, hemoglobin, plasma, hepatic glycogen, myofibrillar fragmentation index (MFI) and water holding capacity (WHC) of surubins. However, with increased resting time, there was a significant decrease in muscle glycogen and an increase in blood pH and blood bicarbonate levels. Additionally, respiratory parameters showed an increase in pO₂ and, consequently, in O₂ saturation and a decrease in pCO₂.The hematocrit and MCV values of the surubins after 24 hours of resting decreased significantly. In the first hours of resting, the highest values of erythrocytes and CHCM were observed. The lowest level of stress was observed for fish having 24 hours of resting. Fish having longer resting periods (8 and 24 hours) presented fillets with a higher pH (P <0.05) and the rigor mortis establishment time was shorter for the first 2 hours and 24 hours of resting time. There was a linear decrease in fillet lightness and an increase in the intensity of red (CIE a*) color up to 24 hours when resting was increased. In CIE b*, a linear decrease (P <0.05) of the yellow intensity of the fillets was observed as the surubim resting time increased. A resting time of 4 to 8 hours before slaughter is effective in reestablishing homeostasis after transporting surubim, providing fillets with higher quality and a greater length of the pre-rigor mortis period.

Tryptophan supplementation helps totoaba (Totoaba macdonaldi) juveniles to regain homeostasis in high-density culture conditions

High-density culture brings with it chronic stress situations that affect fish welfare. In order to evaluate the effect of tryptophan (Trp) levels on the response to stress, Totoaba macdonaldi juveniles were stocked at low (13.5 kg m^-3) and high (27.0 kg m^-3) densities (32.5 and 56.4 kg m^-3, respectively, at the end of the experiment) in 100-L tanks and fed for 63 days with experimental diets containing different Trp levels: control diet CD0.42 (0.42%) and three supplemented diets with 0.99, 1.55 and 2.19% (0.99Trp, 1.55Trp and 2.19Trp, respectively) (three tanks × density × diet). The high-density stocking fed with CD0.42 diets showed significantly increased blood parameters. Trp decreased catalase (CAT) activity in low- and high-density stocking, while the superoxide dismutase (SOD) activity showed no difference. Serotonin (5-hydroxytryptamine, 5-HT) content decreased, and the serotonin turnover ratio (5-HIAA:5-HT) increased in the brains of fish fed with the CD0.42 diet. Indeed, Trp-supplemented diets helped to restore homeostasis in high-density growth conditions as evaluated by the hematological and plasma parameters as well as the serotonergic activity. When the fish were provided a diet containing moderate Trp levels, plasma cortisol increased under high-density conditions. However, no differences were observed among stock densities when totoaba were fed with the 2.19Trp diet. Notably, survival was unaffected by both Trp or densities, but weight gain (WG) decreased with the dietary Trp levels in the high density culture. In sum, Trp supplementation decreased the parameter values linked to stress response on totoaba juveniles cultured at high stock densities.

Thermal Range and Physiological Tolerance Mechanisms in Two Shark Species from the Northwest Atlantic

Spiny dogfish (Squalus acanthias) and smoothhound (Mustelus canis) sharks in the northwest Atlantic undergo seasonal migrations driven by changes in water temperature. However, the recognized thermal habitats of these regional populations are poorly described. Here, we report the thermal range, catch frequency with bottom temperature, and catch frequency with time of year for both shark species in Narragansett Bay, Rhode Island. Additionally, we describe levels of two thermal stress response indicators, heat-shock protein 70 and trimethylamine N-oxide, with an experimental increase in water temperature from 15 °C to 21 °C. Our results show that S. acanthias can be found in this region year-round and co-occurs with M. canis from June to November. Further, adult S. acanthias routinely inhabits colder waters than M. canis (highest catch frequencies at bottom temperatures of 10 °C and 21 °C, respectively), but both exhibit similar upper thermal ranges in this region (bottom temperatures of 22-23 °C). Additionally, acute exposure to a 6 °C increase in water temperature for 72 hours leads to a nearly threefold increase in heat-shock protein 70 levels in S. acanthias but not M. canis. Therefore, these species display differences in their thermal tolerance and stress response with experimental exposure to 21 °C, a common summer temperature in Narragansett Bay. Further, in temperature-stressed S. acanthias there is no accumulation of trimethylamine N-oxide. At the whole-organism level, elasmobranchs' trimethylamine N-oxide regulatory capacity may be limited by other factors. Alternatively, elasmobranchs may not rely on trimethylamine N-oxide as a primary thermal protective mechanism under the conditions tested. Findings from this study are in contrast with previous research conducted with elasmobranch cells in vitro that showed accumulation of trimethylamine N-oxide after thermal stress and subsequent suppression of the heat-shock protein 70 response.

How different rearing temperatures affect growth and stress status of Siberian sturgeon Acipenser baerii larvae

Environmental temperature is one of the critical factors affecting fish development. The aim of this study was to examine the impact of three different rearing temperatures (16, 19 and 22°C) throughout the endogenous feeding phase of the Siberian sturgeon Acipenser baerii. This was performed by assessing (a) larval survival and growth; (b) immunofluorescence localization and expression of genes involved in muscle development and growth - myog and Igf1; and (c) stress status through the expression of thermal stress genes - Hsp70, Hsp90α and Hsp90β - and whole body cortisol. Overall survival rate and larval weight did not differ significantly across temperatures. Larvae subjected to 22°C showed faster absorption of the yolk-sac than larvae subjected to 19 or 16°C. Both at schooling and at the end of the trial, larvae reared at 16°C showed significantly lower levels of cortisol than those reared at 19 or 22°C. IGF-1 immunopositivity was particularly evident in red muscle at schooling stage in all temperatures. The expression of all Hsps as well as the myog and Igf1 genes was statistically higher in larvae reared at 16°C but limited to the schooling stage. Cortisol levels were higher in larvae at 22°C, probably because of the higher metabolism demand rather than a stress response. The observed apparent incongruity between Hsps gene expression and cortisol levels could be due to the lack of a mature system. Further studies are necessary, especially regarding the exogenous feeding phase, in order to better understand if this species is actually sensitive to thermal stress.

Effects of temperature on the transcriptomes of pituitary and liver in Golden Pompano Trachinotus blochii

Fish growth can be modulated dynamically through the brain-pituitary-liver regulation axis. In the present study, whole transcriptomes of the pituitary and liver from Golden Pompano Trachinotus blochii were sequenced in seawater at 20 °C (T_low) and 25 °C (T_high). A total of 187,277,583 paired-end reads were assembled to obtain 100,495 transcripts, corresponding to 83,974 genes. These reads were mapped to T. blochii transcripts, and the mapping accuracy ranged from 80.4 to 94.9%. Two lists of differentially expressed genes were obtained by comparisons of pituitary and liver T_low versus T_high groups, comprising 458 and 205 genes, respectively. Of these, 33 differentially expressed genes were common between the two lists. Twelve GO terms were overrepresented for the 458 differentially expressed genes in the pituitary, and it is noteworthy that the GO term galanin receptor activity (GO: 0004966) related to the modulation of appetite and metabolism, whose genes made up half of all assembled genes in the term. For the 205 differentially expressed genes in the liver, 19 overrepresented GO terms were mainly related to immune regulation, digestion, and protein metabolism. Among the common differentially expressed genes, there were 32 genes that had identical changing trends in both pituitary and liver comparisons. Furthermore, two GO terms inorganic diphosphatase activity and MHC protein complex were overrepresented. These results indicate that the brain could regulate pituitary function through galanin signal mechanism and that the metabolism of liver was further optimized to modulate immunity and growth under different temperatures.

Protective effects of seaweed supplemented diet on antioxidant and immune responses in European seabass (Dicentrarchus labrax) subjected to bacterial infection

European seabass (Dicentrarchus labrax) production is often hampered by bacterial infections such as photobacteriosis caused by Photobacterium damselae subsp. piscicida (Phdp). Since diet can impact fish immunity, this work investigated the effect of dietary supplementation of 5% Gracilaria sp. aqueous extract (GRA) on seabass antioxidant capacity and resistance against Phdp. After infection, mortality was delayed in fish fed GRA, which also revealed increased lysozyme activity levels, as well as decreased lipid peroxidation, suggesting higher antioxidant capacity than in fish fed a control diet. Dietary GRA induced a down-regulation of hepatic stress-responsive heat shock proteins (grp-78, grp-170, grp-94, grp-75), while bacterial infection caused a down-regulation in antioxidant genes (prdx4 and mn-sod). Diet and infection interaction down-regulated the transcription levels of genes associated with oxidative stress response (prdx5 and gpx4) in liver. In head-kidney, GRA led to an up-regulation of genes associated with inflammation (il34, ccr9, cd33) and a down-regulation of genes related to cytokine signalling (mif, il1b, defb, a2m, myd88). Additionally, bacterial infection up-regulated immunoglobulins production (IgMs) and down-regulated the transcription of the antimicrobial peptide leap2 in head kidney. Overall, we found that GRA supplementation modulated seabass resistance to Phdp infection.

Oxidative attack during temperature fluctuation challenge compromises liver protein homeostasis of a temperate fish model

Seasonal variations in water temperature are a natural stressor of temperate fish that affect growth performance and metabolism globally. Gilthead sea bream is one of the most economically interesting species in the Mediterranean; but its liver metabolism is affected by the cold season. However, the effects of cold on protein turnover mechanisms have hardly been studied. Here, we study the relationship between liver oxidative status and protein homeostasis pathways during a 50-day low temperature period at 14 °C, and subsequent recovery at two times: 7 days (early recovery) and 30 days (late recovery). Liver redox status was determined by measuring oxidised lipids and proteins, the glutathione redox cycle and major antioxidant enzymes activities. Protein turnover was analysed via liver protein expression of HSP70 and HSP90; proteasome 26S subunits and polyubiquitination, as markers of the ubiquitin-proteasome system (UPS); and cathepsin D, as a lysosomal protease. Low temperature exposure depressed antioxidant enzyme activities, affecting the glutathione redox cycle and reducing total glutathione levels. Both the UPS and lysosomal pathways were also depressed and consequently, oxidised protein accumulated in liver. Interestingly, both protein oxidation and polyubiquitination tagging depended on protein molecular weight. Despite all these alterations, temperature recovery reverted most consequences of the cold at different rates: with delayed recovery of total glutathione levels and oxidised protein degradation with respect to enzyme activities recovery. All these findings demonstrate that protein liver homeostasis is compromised after chronic cold exposure and could be the cause of liver affectations reported in aquaculture of temperate fish.

The protective effect exerted by dietary borax on toxicity metabolism in rainbow trout (Oncorhynchus mykiss) tissues

The aim of this study was to evaluate the effectiveness of borax (BX) against heavy metal exposure on the transcriptional and biochemical reaction in vivo and alleviating effect on gill and liver tissues of rainbow trout. Due to this aim, fish were fed with different level of BX and/or copper (Cu) (1.25, 2.5 and 5 mg/kg of BX; 500 and 1000 mg/kg of Cu) for 21·days in pre- and co-treatment options. The transcriptional parameters [(heat-shock protein 70 (hsp70), and cytochromes P450 (cyp1a), glutathione peroxidase (GPx), superoxide dismutase (SOD) and catalase (CAT))], antioxidant enzyme activities (SOD, CAT and GPx), malondialdehyde (MDA), oxidative DNA damage (8-hydroxy-2'-deoxyguanosine (8-OHdG) and caspase-3 levels were investigated in different tissues samples of treated and control fish. Our results revealed that antioxidant enzyme activity was increased and levels of 8-OHdG, Caspase-3 and MDA were decreased in the BX and BX combined groups as compared to the copper combination group and to copper-only application during pre- and co-treatment (p < 0.05). Similarly, hsp70 and cyp1a gene expressions were decreased after treatment with BX. As conclusion, we suggest that borax itself is not an antioxidant it supportes antioxidant defense mechanism of fish disrupted by heavy metals.

Domestication and Temperature Modulate Gene Expression Signatures and Growth in the Australasian Snapper Chrysophrys auratus

Identifying genes and pathways involved in domestication is critical to understand how species change in response to human-induced selection pressures, such as increased temperatures. Given the profound influence of temperature on fish metabolism and organismal performance, a comparison of how temperature affects wild and domestic strains of snapper is an important question to address. We experimentally manipulated temperature conditions for F₁-hatchery and wild Australasian snapper (Chrysophrys auratus) for 18 days to mimic seasonal extremes and measured differences in growth, white muscle RNA transcription and hematological parameters. Over 2.2 Gb paired-end reads were assembled de novo for a total set of 33,017 transcripts (N50 = 2,804). We found pronounced growth and gene expression differences between wild and domesticated individuals related to global developmental and immune pathways. Temperature-modulated growth responses were linked to major pathways affecting metabolism, cell regulation and signaling. This study is the first step toward gaining an understanding of the changes occurring in the early stages of domestication, and the mechanisms underlying thermal adaptation and associated growth in poikilothermic vertebrates. Our study further provides the first transcriptome resources for studying biological questions in this non-model fish species.

Environmental pollution and toxic substances: Cellular apoptosis as a key parameter in a sensible model like fish

The industrial wastes, sewage effluents, agricultural run-off and decomposition of biological waste may cause high environmental concentration of chemicals that can interfere with the cell cycle activating the programmed process of cells death (apoptosis). In order to provide a detailed understanding of environmental pollutants-induced apoptosis, here we reviewed the current knowledge on the interactions of environmental chemicals and programmed cell death. Metals (aluminum, arsenic, cadmium, chromium, cobalt, zinc, copper, mercury and silver) as well as other chemicals including bleached kraft pulp mill effluent (BKME), persistent organic pollutants (POPs), and pesticides (organo-phosphated, organo-chlorinated, carbamates, phyretroids and biopesticides) were evaluated in relation to apoptotic pathways, heat shock proteins and metallothioneins. Although research performed over the past decades has improved our understanding of processes involved in apoptosis in fish, yet there is lack of knowledge on associations between environmental pollutants and apoptosis. Thus, this review could be useful tool to study the cytotoxic/apoptotic effects of different pollutants in fish species.

Effects of elevated temperature on osmoregulation and stress responses in Atlantic salmon Salmo salar smolts in fresh water and seawater

Smolting in Atlantic salmon Salmo salar is a critical life-history stage that is preparatory for downstream migration and entry to seawater that is regulated by abiotic variables including photoperiod and temperature. The present study was undertaken to determine the interaction of temperature and salinity on salinity tolerance, gill osmoregulatory proteins and cellular and endocrine stress in S. salar smolts. Fish were exposed to rapid changes in temperature (from 14 to 17, 20 and 24°C) in fresh water (FW) and seawater (SW), with and without prior acclimation and sampled after 2 and 8 days. Fish exposed simultaneously to SW and 24°C experienced 100% mortality, whereas no mortality occurred in any of the other groups. The highest temperature also resulted in poor ion regulation in SW with or without prior SW acclimation, whereas no substantial effect was observed in FW. Gill Na⁺ -K⁺ -ATPase (NKA) activity increased in SW fish compared to FW fish and decreased with high temperature in both FW and SW. Gill Nkaα1a abundance was high in FW and Nkaα1b and Na⁺ -K⁺ -2Cl- cotransporter high in SW, but all three were lower at the highest temperature. Gill Hsp70 levels were elevated in FW and SW at the highest temperature and increased with increasing temperature 2 days following direct transfer to SW. Plasma cortisol levels were elevated in SW at the highest temperature. Our results indicate that there is an important interaction of salinity and elevated temperature on osmoregulatory performance and the cellular stress response in S. salar, with an apparent threshold for osmoregulatory failure in SW above 20°C.

Response of antioxidant enzymes to Cd and Pb exposure in water flea Daphnia magna: Differential metal and age - Specific patterns

To investigate oxidative stress responses to cadmium and lead, the freshwater water flea Daphnia magna was exposed to Cd and Pb for 48 h. Following treatment with sub-lethal concentrations, intracellular reactive oxygen species (ROS) levels, as well as modulation of multiple biomarker, such as superoxide dismutase (SOD) activity, glutathione (GSH) contents, glutathione S-transferase (GST) activity, antioxidant enzyme - coding genes (three GST isoforms, glutaredoxin [GRx], glutathione peroxidase [GPx], and thioredoxin [TRx]), and stress-response proteins (heat shock protein 70 [Hsp70] and Hsp90) were examined. The results showed that intracellular ROS level was not changed at 24 h, but reduced at 48 h. Levels of total GSH content were reduced by Cd, but highly induced by Pb. SOD and GST activities were stimulated 48 h after exposure to Cd and Pb. A significant modulation of oxidative stress marker genes was observed after exposure to each element with different expression patterns depending on the metal and developmental stages. In particular, the expression levels of GST-sigma, HSP70, and HSP90 genes were enhanced in Cd - and Pb - exposed neonates. These findings imply that oxidative stress markers appear to be actively involved in cellular protection against metal-induced oxidative stress in D. magna. This study would facilitate the understanding of the molecular response to Cd and Pb exposure in water fleas.

A macrophysiology approach to watershed science and management

Freshwaters are among the most imperiled ecosystems on the planet such that much effort is expended on environmental monitoring to support the management of these systems. Many traditional monitoring efforts focus on abiotic characterization of water quantity or quality and/or indices of biotic integrity that focus on higher scale population or community level metrics such as abundance or diversity. However, these indicators may take time to manifest in degraded systems and delay the identification and restoration of these systems. Physiological indicators manifest rapidly and portend oncoming changes in populations that can hasten restoration and facilitate preventative medicine for degraded habitats. Therefore, assessing freshwater ecosystem integrity using physiological indicators of health is a promising tool to improve freshwater monitoring and restoration. Here, we discuss the value of using comparative, longitudinal physiological data collected at a broad spatial (i.e. watershed) scale (i.e. macrophysiology) as a tool for monitoring aquatic ecosystem health within and among local watersheds to develop timely and effective management plans. There are emerging tools and techniques available for rapid, cost-effective, and non-lethal physiological sampling and we discuss how these can be integrated into management using fish as sentinel indicators in freshwater. Although many examples of this approach are relatively recent, we foresee increasing use of macrophysiology in monitoring, and advocate for the development of more standard tools for consistent and reliable assessment.

Effect of excessive doses of oxytetracycline on stress-related biomarker expression in coho salmon

Fish are exposed to a wide variety of environmental stressors, such as chemicals and acute changes in temperature. Oxytetracycline (OTC) has been used as an antibiotic for many kinds of bacterial diseases in cultured fish, but excessive doses of OTC are known to cause side effects in fish and can have negative effects on their environment. In the present study, we examined stress-related biomarker expression in response to excessive doses of dietary OTC in coho salmon (Oncorhynchus kisutch). Fish received OTC (100 mg/kg body weight/day) orally for 2 weeks. The percentage of liver to body weight (hepatosomatic index; HSI) and plasma biochemical parameter, alanine aminotransferase (ALT) activity, of the group fed a diet containing OTC were observed to be significantly higher than those of the control group. The total glutathione (tGSH) levels in the liver of OTC-fed fish were four fold higher than those in control fish and double the control levels in muscle and stomach. Plasma tGSH levels in OTC-fed fish were also higher than those in control fish. Expression levels of heat shock protein 70 in the liver, muscle, and stomach decreased by OTC administration. Accordingly, OTC-induced stress might increase the metabolic turnover of GSH due to consumption by scavenging oxidants generated by stress. These results concerning the changing patterns of stress-related biomarkers indicate that excessive doses of OTC fed to coho salmon induce oxidative stress, which might enhance oxidation in the body and result in damage to tissues, especially in the liver. The present results also suggest that tissue-specific damage caused by OTC might already exist in fish.

Effects of dietary dandelion extract on intestinal morphology, antioxidant status, immune function and physical barrier function of juvenile golden pompano Trachinotus ovatus

Intestinal morphology, antioxidant status, immune function and tight junction proteins mRNA expression were examined in golden pompano (Trachinotus ovatus) that fed respectively six diets containing dandelion extracts (DE) at 0, 0.5, 1, 2, 4 and 10 g kg^-1 after 8 weeks feeding. The study indicated that dietary DE significantly improved intestinal antioxidant abilities by increasing SOD, CAT, T-AOC activities and up-regulating intestinal cat, gpx mRNA levels, but by decreasing MDA content and down-regulating intestinal keap1 mRNA levels in golden pompano. Meanwhile, dietary DE improved intestinal morphology, suggesting that enhances intestinal digestion and absorption, by increasing muscle thickness, villus length, villus width and villus number in the foregut and hindgut; as well as villus number, villus width and muscle thickness in the midgut (P < .05). Dietary DE enhanced intestinal barrier function by increasing intestinal zo-1 and occludin mRNA levels, but by decreasing the mRNA levels of claudin-12 and claudin-15. Furthermore, dietary DE improved intestinal immunity via increasing goblet cells numbers and regulating expression of immune-related genes. In conclusion, dietary DE supplementation promoted intestine health by improving intestine morphology, immunity, antioxidant abilities and intestinal barrier in golden pompano.

Allostatic Load and Stress Physiology in European Seabass (Dicentrarchus labrax L.) and Gilthead Seabream (Sparus aurata L.)

The present study aimed to compare effects of increasing chronic stress load on the stress response of European seabass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata) to identify neuroendocrine functions that regulate this response. Fish were left undisturbed (controls) or exposed to three levels of chronic stress for 3 weeks and then subjected to an acute stress test (ACT). Chronic stress impeded growth and decreased feed consumption in seabass, not in seabream. In seabass basal cortisol levels are high and increase with stress load; the response to a subsequent ACT decreases with increasing (earlier) load. Basal cortisol levels in seabream increase with the stress load, whereas the ACT induced a similar response in all groups. In seabass and seabream plasma α-MSH levels and brain stem serotonergic activity and turnover were similar and not affected by chronic stress. Species-specific molecular neuro-regional differences were seen. In-situ hybridization analysis of the early immediate gene cfos in the preoptic area showed ACT-activation in seabream; in seabass the expression level was not affected by ACT and seems constitutively high. In seabream, expression levels of telencephalic crf, crfbp, gr1, and mr were downregulated; the seabass hypothalamic preoptic area showed increased expression of crf and gr1, and decreased expression of mr, and this increased the gr1/mr ratio considerably. We substantiate species-specific physiological differences to stress coping between seabream and seabass at an endocrine and neuroendocrine molecular level. Seabass appear less resilient to stress, which we conclude from high basal activities of stress-related parameters and poor, or absent, responses to ACT. This comparative study reveals important aquaculture, husbandry, and welfare implications for the rearing of these species.

Effects of partial dietary supplementation of fish meal with soymeal on the stress and apoptosis response in the digestive system of common dentex (Dentex dentex)

Background

Soybean is a common alternative protein source of plant origin in aquafeeds as it has a reasonably balanced amino acid profile and is widely available. This study aimed to investigate the influence of partial substitution of fish meal with soy meal on cytoprotective pathways and apoptosis in the digestive system of common dentex (Dentex dentex), using the activation of Hsp70, p38 MAPK, Bcl-2 and caspase-3. The experimental approach involved feeding of common dentex with three isoprotein and isoenergetic diets that contained fish meal as a protein source (FM), partial replacement of fish meal by soy meal 25% (SM25) and 40% (SM40) for 3 months.

Results

The SM40 diet induced Hsp70 activation only in the middle part of intestine. On the other hand, both SM25 and SM40 diets diminished the phosphorylation of p38 MAPK in the anterior and the middle part of intestine, whereas only SM25 induced p38 MAPK phosphorylation in the stomach. Moreover, a decrease in the levels of caspase-3 activity was observed in the middle and posterior intestine, as well as in the stomach after feeding with SM25 diets. Furthermore, Bcl-2 levels were increased by SM40 in the anterior and by SM25 in the middle part of intestine.

Conclusions

SM25 and SM40 diets elicited a tissue and soy concentration specific cellular and cell protective response in the different parts of the digestive tract in common dentex.

Upper thermal limits of growth in brook trout and their relationship to stress physiology

Despite the threat of climate change, the physiological mechanisms responsible for reduced performance at high temperatures remain unclear for most species. Elevated but sublethal temperatures may act via endocrine and cellular stress responses to limit performance in important life-history traits such as growth. Here, brook trout (Salvelinus fontinalis) subjected to chronically elevated or daily oscillating temperatures were monitored for growth and physiological stress responses. Growth rate decreased at temperatures above 16°C and was negative at 24°C, with an estimated upper limit for positive growth of 23.4°C. Plasma cortisol increased with temperature and was 12- and 18-fold higher at 22 and 24°C, respectively, than at 16°C, whereas plasma glucose was unaffected by temperature. Abundance of heat shock protein 70 (HSP70) in the gill increased with temperature and was 11- and 56-fold higher at 22°C and 24°C, respectively, than at 16°C. There was no relationship between temperature and plasma Cl−, but there was a 53% and 80% decrease in gill Na+/K+-ATPase activity and abundance at 24°C in comparison with 16°C. Daily temperature oscillations of 4°C or 8°C (19–23°C or 17–25°C) were compared with 21°C controls. Growth rate decreased with temperature and was 43% and 35% lower by length and mass, respectively, in the 8°C daily oscillation treatment than in the controls. There was no effect of temperature oscillation on plasma cortisol or glucose levels. In contrast, gill HSP70 abundance increased with increasing daily oscillation and was 40- and 700-fold greater at 4°C and 8°C daily oscillation, respectively, than in the constant temperature controls. In individuals exposed to 17–25°C diel oscillations for 4 days and then allowed to recover at 21°C, gill HSP70 abundance was still elevated after 4 days recovery, but not after 10 days. Our results demonstrate that elevated temperatures induce cellular and endocrine stress responses and provide a possible mechanism by which growth is limited at elevated temperatures. Temperature limitations on growth may play a role in driving brook trout distributions in the wild.

Dietary supplementation of curcumin augments heat stress tolerance through upregulation of nrf-2-mediated antioxidative enzymes and hsps in Puntius sophore

Heat stress is one of the major environmental concerns in global warming regime and rising temperature has resulted in mass mortalities of animals including fishes. Therefore, strategies for high temperature stress tolerance and ameliorating the effects of heat stress are being looked for. In an earlier study, we reported that Nrf-2 (nuclear factor E2-related factor 2) mediated upregulation of antioxidative enzymes and heat shock proteins (Hsps) provide survivability to fish under heat stress. In this study, we have evaluated the ameliorative potential of dietary curcumin, a potential Nrf-2 inducer in heat stressed cyprinid Puntius sophore. Fishes were fed with diet supplemented with 0.5, 1.0, and 1.5% curcumin at the rate 2% of body weight daily in three separate groups (n = 40 in each group) for 60 days. Fishes fed with basal diet (without curcumin) served as the control (n = 40). Critical thermal maxima (CTmax) was determined for all the groups (n = 10, in duplicates) after the feeding trial. Significant increase in the CTmax was observed in the group fed with 1.5% curcumin- supplemented fishes whereas it remained similar in groups fed with 0.5%, and 1% curcumin-supplemented diet, as compared to control. To understand the molecular mechanism of elevated thermotolerance in the 1.5% curcumin supplemented group, fishes were given a sub-lethal heat shock treatment (36 °C) for 6 h and expression analysis of nrf-2, keap-1, sod, catalase, gpx, and hsp27, hsp60, hsp70, hsp90, and hsp110 was carried out using RT-PCR. In the gill, expression of nrf-2, sod, catalase, gpx, and hsp60, hsp70, hsp90, and hsp110 was found to be elevated in the 1.5% curcumin-fed heat-shocked group compared to control and the basal diet-fed, heat-shocked fishes. Similarly, in the liver, upregulation in expression of nrf-2, sod, catalase, and hsp70 and hsp110 was observed in 1.5% curcumin supplemented and heat shocked group. Thus, this study showed that supplementation of curcumin augments tolerance to high temperature stress in P. sophore that could be attributed to nrf-2-induced upregulation of antioxidative enzymes sod, catalase, gpx, and the hsps.

Investigation of 8-OHdG, CYP1A, HSP70 and transcriptional analyses of antioxidant defence system in liver tissues of rainbow trout exposed to eprinomectin

Eprinomectin (EPM), a member of avermectin family, is a semi-synthetic antibiotic. It has been known that avermectin family enters the aquatic environments and adversely affects the aquatic organisms. Effects of EPM is fully unknown in aquatic organisms especially fish, thus the aim of the present study was to investigate transcriptional changes (sod, cat, gpx) and activities of some antioxidant enzymes (superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) and malondialdehyde (MDA) levels, oxidative DNA damage (8-hydroxy-2-deoxyguanosine (8-OHdG)) and transcriptional changes of heat shock protein 70 (HSP70), and cytochromes P4501A (CYP1A) in liver tissues of rainbow trout exposed to sublethal EPM concentration (0.001 μg/L, 0.002 μg/L, 0.01 μg/L, 0.05 μg/L) for 24 h, 48 h, 72 h and 96 h. The decrease in antioxidant enzyme (SOD, CAT and GPx) activity, transcriptional changes (sod, cat, gpx, HSP70 and CYP1A genes) and increase in MDA level and activity of 8-OHdG in a dose-time-dependent manner in the liver of rainbow trout were observed. The down-regulated of antioxidant (sod, cat and gpx), HSP70 and CYP1A obviously, the severity of which increased with the concentration of EPM and exposure time. The results imply that EPM could induce oxidative damage to the liver tissue of rainbow trout. The information presented in this study is helpful to understand the mechanism of veterinary pharmaceuticals-induced oxidative stress in fishes.