Synergistic effects of acute warming and low pH on cellular stress responses of the gilthead seabream Sparus aurata

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.

Responses of marine trophic levels to the combined effects of ocean acidification and warming

Marine organisms are simultaneously exposed to anthropogenic stressors associated with ocean acidification and ocean warming, with expected interactive effects. Species from different trophic levels with dissimilar characteristics and evolutionary histories are likely to respond differently. Here, we perform a meta-analysis of controlled experiments including both ocean acidification and ocean warming factors to investigate single and interactive effects of these stressors on marine species. Contrary to expectations, we find that synergistic interactions are less common (16%) than additive (40%) and antagonistic (44%) interactions overall and their proportion decreases with increasing trophic level. Predators are the most tolerant trophic level to both individual and combined effects. For interactive effects, calcifying and non-calcifying species show similar patterns. We also identify climate region-specific patterns, with interactive effects ranging from synergistic in temperate regions to compensatory in subtropical regions, to positive in tropical regions. Our findings improve understanding of how ocean warming, and acidification affect marine trophic levels and highlight the need for deeper consideration of multiple stressors in conservation efforts.

Neuromolecular responses in disrupted mutualistic cleaning interactions under future environmental conditions

BACKGROUND

Mutualistic interactions, which constitute some of the most advantageous interactions among fish species, are highly vulnerable to environmental changes. A key mutualistic interaction is the cleaning service rendered by the cleaner wrasse, Labroides dimidiatus, which involves intricate processes of social behaviour to remove ectoparasites from client fish and can be altered in near-future environmental conditions. Here, we evaluated the neuromolecular mechanisms behind the behavioural disruption of cleaning interactions in response to future environments. We subjected cleaner wrasses and surgeonfish (Acanthurus leucosternon, serving as clients) to elevated temperature (warming, 32 °C), increased levels of CO2 (high CO2, 1000 ppm), and a combined condition of elevated CO2 and temperature (warming and high CO2, 32 °C, and 1000 ppm) for 28 days.

RESULTS

Each of these conditions resulted in behavioural disruptions concerning the motivation to interact and the quality of interaction (high CO2 - 80.7%, warming - 92.6%, warming and high CO2 - 79.5%, p < 0.001). Using transcriptomics of the fore-, mid-, and hindbrain, we discovered that most transcriptional reprogramming in both species under warming conditions occurred primarily in the hind- and forebrain. The associated functions under warming were linked to stress, heat shock proteins, hypoxia, and behaviour. In contrast, elevated CO2 exposure affected a range of functions associated with GABA, behaviour, visual perception, thyroid hormones and circadian rhythm. Interestingly, in the combined warming and high CO2 condition, we did not observe any expression changes of behaviour. However, we did find signs of endoplasmic reticulum stress and apoptosis, suggesting not only an additive effect of the environmental conditions but also a trade-off between physiological performance and behaviour in the cleaner wrasse.

CONCLUSIONS

We show that impending environmental shifts can affect the behaviour and molecular processes that sustain mutualistic interactions between L. dimidiatus and its clients, which could have a cascading effect on their adaptation potential and possibly cause large-scale impacts on coral reef ecosystems.

Impacts of rising temperatures and water acidification on the oxidative status and immune system of aquatic ectothermic vertebrates: A meta-analysis

Species persistence in the Anthropocene is dramatically threatened by global climate change. Large emissions of carbon dioxide (CO₂) from human activities are driving increases in mean temperature, intensity of heatwaves, and acidification of oceans and freshwater bodies. Ectotherms are particularly sensitive to CO₂-induced stressors, because the rate of their metabolic reactions, as well as their immunological performance, are affected by environmental temperatures and water pH. We reviewed and performed a meta-analysis of 56 studies, involving 1259 effect sizes, that compared oxidative status or immune function metrics between 42 species of ectothermic vertebrates exposed to long-term increased temperatures or water acidification (≥48 h), and those exposed to control parameters resembling natural conditions. We found that CO₂-induced stressors enhance levels of molecular oxidative damages in ectotherms, while the activity of antioxidant enzymes was upregulated only at higher temperatures, possibly due to an increased rate of biochemical reactions dependent on the higher ambient temperature. Differently, both temperature and water acidification showed weak impacts on immune function, indicating different direction (increase or decrease) of responses among immune traits. Further, we found that the intensity of temperature treatments (Δ°C) and their duration, enhance the physiological response of ectotherms, pointing to stronger effects of prolonged extreme warming events (i.e., heatwaves) on the oxidative status. Finally, adult individuals showed weaker antioxidant enzymatic responses to an increase in water temperature compared to early life stages, suggesting lower acclimation capacity. Antarctic species showed weaker antioxidant response compared to temperate and tropical species, but level of uncertainty in the antioxidant enzymatic response of Antarctic species was high, thus pairwise comparisons were statistically non-significant. Overall, the results of this meta-analysis indicate that the regulation of oxidative status might be one key mechanism underlying thermal plasticity in aquatic ectothermic vertebrates.

Red porgy's (Pagrus pagrus) cellular physiology and antioxidant defense in response to seasonality

Physiological stress patterns of marine organisms in their natural habitats are considerably complex in space and time. These patterns can eventually contribute in the shaping of fish' thermal limits under natural conditions. In the view of the knowledge gap regarding red porgy's thermal physiology, in combination with the characterization of the Mediterranean Sea as a climate change ''hotspot'', the aim of the present study was to investigate this species biochemical responses to constantly changing field conditions. To achieve this goal, Heat Shock Response (HSR), MAPKs pathway, autophagy, apoptosis, lipid peroxidation and antioxidant defense were estimated and exhibited a seasonal pattern. In general, all the examined biochemical indicators expressed high levels parallel to the increasing seawater temperature in spring, although several bio-indicators have shown increased levels when fish were cold-acclimatized. Similar to other sparids, the observed patterns of physiological responses in red porgy may support the concept of eurythermy.

Thermal Stress Induces Metabolic Responses in Juvenile Qingtian Paddy Field Carp Cyprinus carpio var qingtianensis

Extreme fluctuations in water temperature lead to significant economic losses for the aquaculture industry. Cyprinus carpio var qingtianensis (locally called Qingtian paddy field carp), is a local variety commonly found in Zhejiang province, China. Unlike traditional aquaculture environments, the water temperature range between day and night in the rice field environment is much larger, and the high temperature in summer may exceed the growth threshold of fish because there is no manual intervention; therefore, the study of how the Qingtian paddy field carp (PF carp) adapts to high-temperature conditions can shed light how the species adapt to the rice field environment. To investigate the molecular mechanisms of this fish under thermal stress, the liver metabolomics of Qiangtian paddy field carp (PF carp) were analyzed. In this study, metabolomics was used to examine the metabolic reaction of PF carp (102 days old, 104.69 ± 3.08 g in weight, 14.65 ± 0.46 cm in length) at water temperatures of 28 °C (control group, CG), 34 °C (experimental group (EG) 34), and 38 °C (EG38). The results show that 175 expression profile metabolites (DEMs), including 115 upregulated and 60 downregulated metabolites, were found in the CG vs. EG34. A total of 354 DEMs were inspected in CG vs. EG38, with 85 metabolites downregulated and 269 metabolites upregulated. According to the pathway enrichment study, various pathways were altered by thermal stress, including those of lipid, amino-acid, and carbohydrate metabolism. Our study presents a potential metabolic profile for PF carp under thermal stress. It also demonstrates how the host responds to thermal stress on a metabolic and molecular level.

Dietary Tenebrio molitor Larvae Meal Inclusion Exerts Tissue-Specific Effects on Cellular, Metabolic, and Antioxidant Status in European Sea Bass (Dicentrarchus labrax) and Gilthead Seabream (Sparus aurata)

The present study addresses the effects of dietary Tenebrio molitor (TM) larvae meal inclusion on cytoprotective, cell death pathways, antioxidant defence, and intermediate metabolism in the heart, muscle, and digestive tract of gilthead seabream (Sparus aurata) and European sea bass (Dicentrarchus labrax). Three experimental diets were formulated to contain 0%, 25%, or 50% inclusion TM levels. Heat Shock Proteins (HSPs) induction was apparent in both species' muscle at 50% inclusion. Conversely, p44/42 Mitogen-Activated Protein Kinase (MAPK) activation was increased (p < 0.05) in both species' muscle and digestive tract at 25% inclusion. Regarding the apoptotic machinery, TM inclusion exerted no influence on gilthead seabream, while suppression through autophagy may have occurred in the muscle. However, significant apoptosis (p < 0.05) was evident in European sea bass muscle and digestive tract. Both fish species' heart seemed to additionally rely on lipids compared to muscle and digestive tract. In contrast to gilthead seabream, European sea bass exhibited increased (p < 0.05) antioxidant activity at 50% TM inclusion. The present findings highlight the dietary derived induction of cellular responses in a species- and tissue-specific manner, whereas European sea bass appears to be more susceptible to TM inclusion.

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

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

Seasonal cellular stress phenomena and phenotypic plasticity in land snail Helix lucorum populations from different altitudes

Temperature, a major abiotic environmental factor, regulates various physiological functions in land snails and therefore determines their biogeographical distribution. Thus, species with different distributions may present different thermal tolerance limits. Additionally, the intense reactivation of snail metabolic rate upon arousal from hibernation or estivation may provoke stress. Land snails, Helix lucorum, display a wide altitudinal distribution resulting in populations being exposed to different seasonal temperature variations. The aim of the present study was to investigate the expression of heat shock proteins (Hsps), mitogen activated protein kinases (MAPKs) and proteins that are related to apoptosis (Bcl-2, ubiquitin), that have 'cytoprotective' roles and are also considered to be reliable indicators of stress because of their crucial role in maintaining cellular homeostasis. These proteins were assessed in H. lucorum individuals from two different populations, one at Axios (sea level, 0 m) and the other at Kokkinopilos (Olympus, 1250 m), as well as after mutual population exchanges, in order to find out whether the different responses of these stress-related proteins depend solely on the environmental temperature. The results showed seasonally altered levels in all studied proteins in the hepatopancreas and foot of snails, both among different populations and between the same populations exposed to varying altitudes. However, individuals of the same population in their native habitat or acclimatized to a different habitat showed a relatively similar pattern of expression, supporting the induction of the specific proteins according to the life history of each species.

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

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

Advances in understanding the impacts of global warming on marine fishes farmed offshore: Sparus aurata as a case study

Monitoring variations in proteins involved in metabolic processes, oxidative stress responses, cell signalling and protein homeostasis is a powerful tool for developing hypotheses of how environmental variations affect marine organisms' physiology and biology. According to the oxygen- and capacity-limited thermal tolerance hypothesis, thermal acclimation mechanisms such as adjusting the activities of enzymes of intermediary metabolism and of antioxidant defence mechanisms, inducing heat shock proteins (Hsps) or activating mitogen-activated protein kinases may all shift tolerance windows. Few studies have, however, investigated the molecular, biochemical and organismal responses by fishes to seasonal temperature variations in the field to link these to laboratory findings. Investigation of the impacts of global warming on fishes farmed offsore, in the open sea, can provide a stepping stone towards understanding effects on wild populations because they experience similar environmental fluctuations. Over the last 30 years, farming of the gilthead sea bream Sparus aurata (Linnaeus 1758) has become widespread along the Mediterranean coastline, rendering this species a useful case study. Based on available information, the prevailing seasonal temperature variations expose the species to the upper and lower limits of its thermal range. Evidence for this includes oxygen restriction, reduced feeding, reduced responsiveness to environmental stimuli, plus a range of molecular and biochemical indicators that change across the thermal range. Additionally, close relationships between biochemical pathways and seasonal patterns of metabolism indicate a connection between energy demand and metabolic processes on the one hand, and cellular stress responses such as oxidative stress, inflammation and autophagy on the other. Understanding physiological responses to temperature fluctuations in fishes farmed offshore can provide crucial background information for the conservation and successful management of aquaculture resources in the face of global change.

Season specific influence of projected ocean changes on the response to cadmium of stress-related genes in Mytilus galloprovincialis

Anthropogenic inputs of carbon dioxide in the atmosphere are driving ocean warming and acidification. The potential threat represented by these changes for marine species could be amplified in coastal areas, characterized by higher levels of pollutants. In addition, temperate organisms may exhibit a different seasonal tolerance to stressors influenced by fluctuations of environmental and physiological factors. In this study, Mediterranean mussels Mytilus galloprovincialis collected both in summer and winter were exposed to combinations of two temperatures (SST, seasonal surface temperature and SST+5 °C) and two levels of pH (8.20 and 7.40) in clean or cadmium contaminated seawater (20 μg/L Cd). mRNA levels of genes related to metal-induced stress response were investigated, including metallothionein mt-20, heat-shock protein hsp70, superoxide dismutase Cu/Zn-sod, catalase cat, glutathione peroxidase gpx1 and glutathione S-transferase gst-pi. To further elucidate if tissues with different physiological roles could exhibit different responsiveness, such analyses were carried out in digestive gland and in gills of exposed mussels. mt-20 mRNA increase after Cd-exposure was higher in the digestive gland than in the gills, with few modulations by temperature or pH only in the latter. Acidification, alone or in combination with other stressors, increased hsp70 mRNA, with seasonal- and tissue-specificities (higher in summer and in digestive gland). Among antioxidants, gpx1 mRNA was affected by Cd in both tissues and seasons, with further modulations due to pH and temperature variation tissue- and season-specific; in winter the combination of Cd, warming and acidification affected Cu/Zn-sod both in digestive gland and gills and cat only in gills, while weak seasonal variations were observed for gst-pi transcripts only in digestive gland. The overall results highlighted the importance of considering seasonality and responsiveness of different tissues to predict the effects of sudden changes in environmental parameters on responsiveness to and toxicity of chemicals in marine coastal organisms.

Metabolomics investigation of summer mortality in New Zealand Greenshell™ mussels (Perna canaliculus)

Increasing water temperatures due to climate change have resulted in more frequent high mortality events of New Zealand Greenshell™ mussels (Perna canaliculus Gmelin 1791). These events have significant impacts within mussel farms which support a major shellfish industry for New Zealand. The present study investigates metabolic responses of farmed mussels during a summer mortality event in order to identify health impacts and elucidate mechanistic effects of external stressors on mussels. A gas chromatography-mass spectrometry (GC-MS)-based metabolomics approach was used to identify metabolic perturbations and flow cytometry assays were used to assess viability, oxidative stress and apoptosis of haemocytes from healthy and unhealthy mussels during a summer mortality event. The results showed significantly higher mortality and apoptosis of haemocytes in unhealthy mussels compared to healthy mussels. Reactive oxygen species (ROS) production, which is an indicator of oxidative stress was very high in both mussel groups, but no differences were observed between the two mussel groups. Metabolomics revealed alterations of many metabolites in both haemolymph and hepatopancreas (digestive gland) of unhealthy mussels compared to healthy mussels, reflecting perturbations in several molecular pathways, including energy metabolism, amino acid metabolism, protein degradation/tissue damage and oxidative stress. An increased level of itaconic acid which is an antimicrobial metabolite and biomarker of pathogen infection was observed in haemolymph, but not in hepatopancreas samples. This investigation provides the first detailed metabolic characterization of mussel immune responses to a summer mortality event and illustrates the benefits of using an integrated metabolomics and flow cytometry workflow for mussel health assessment and biomarker identification for summer mortality early detection.

Seasonal cellular stress responses of commercially important invertebrates at different habitats of the North Aegean Sea

In many aquatic species, the negative effect of temperature variations has a significant impact on physiological performance since beyond Tp (upper pejus) and Tc (critical temperatures), according to the oxygen- and capacity-limited thermal tolerance (OCLTT), transition to hypoxemia and mitochondrial metabolism triggers the increase in reactive oxygen species (ROS) production. However, climate change may have different spatial impact, and as a result, areas with more favorable climatic conditions (refugia) can be identified. The aim of the present study, based on cellular stress responses, is the demarcation of these areas and the preservation of commercially important marine species. Under this prism, individuals of the species Callinectes sapidus (blue crab), Sepia officinalis (common cuttlefish), Holothuria tubulosa (sea cucumber) and Venus verrucosa (clam) from Thermaikos, Pagasitikos and Vistonikos gulf were collected seasonally. The results showed an increase in the levels of several stress indicators exhibiting the triggering of Heat Shock Response, MAPK activation, apoptotic phenomena and increased ubiquitilination during the summer sampling in relation to the spring and autumn samplings concerning blue crab and clam, while no changes were observed for common cuttlefish and sea cucumber. It seems that these cellular responses consist a cytoprotective mechanism against environmental thermal stress. Regarding collection sites, for all examined species, higher cellular stress levels were observed in Pagasitikos, and lower in Vistonikos gulf. This analysis of biochemical and molecular markers is expected to provide a clearer picture for the definition of "refugia" for the above species.

Effect of water temperature on cellular stress responses in meagre (Argyrosomus regius)

Μeagre (Argyrosomus regius) is a newly introduced species in the aquaculture sector characterized by high growth rates and good nutritional value. However, the optimum conditions such as water temperature for the rearing of this species are still under research. The aim of the present study was to investigate several biochemical responses in the heart, muscle, liver, and intestine of meagre reared under different water temperatures (17, 23, and 26 °C) in comparison to the initial acclimation temperature at 20 °C. To assess its cellular stress response, the molecular markers of Hsp70 and Hsp90 induced levels, p38 MAPK and p44/42 MAPK phosphorylated levels, ubiquitin conjugates, and Bcl-2 levels were determined. Moreover, to investigate its antioxidant defense, the activities of superoxide dismutase, catalase, and glutathione reductase were measured. The obtained results in meagre showed a distinct tissue-specific response regarding the variations observed in the studied parameters under different acclimation temperatures. Specifically, most examined tissues presented a decrease in the levels of the examined markers compared to 20 °C, while in the intestine, an increase of Hsp70 and p38 MAPK levels was observed at 23 and 26 °C. However, data on the final weight and length of the fish lead to the conclusion that high water temperatures such as 26 °C might be the best for the rearing of this species. Therefore, it is assumed that the observed differential molecular responses may act in a cell-protective way at all temperatures, irrespectively of the effect of temperature on growth parameters.

Water temperature affects osmoregulatory responses in gilthead sea bream (Sparus aurata L.)

Sea bream (Sparus aurata Linneaus) was acclimated to three salinity concentrations, viz. 5 (LSW), 38 (SW) and 55psμ (HSW) and three water temperatures regimes (12, 19 and 26 °C) for five weeks. Osmoregulatory capacity parameters (plasma osmolality, sodium, chloride, cortisol, and branchial and renal Na⁺,K⁺-ATPase activities) were also assessed. Salinity and temperature affected all of the parameters tested. Our results indicate that environmental temperature modulates capacity in sea bream, independent of environmental salinity, and set points of plasma osmolality and ion concentrations depend on both ambient salinity and temperature. Acclimation to extreme salinity resulted in stress, indicated by elevated basal plasma cortisol levels. Response to salinity was affected by ambient temperature. A comparison between branchial and renal Na⁺,K⁺-ATPase activities appears instrumental in explaining salinity and temperature responses. Sea bream regulate branchial enzyme copy numbers (V_max) in hyperosmotic media (SW and HSW) to deal with ambient temperature effects on activity; combinations of high temperatures and salinity may exceed the adaptive capacity of sea bream. Salinity compromises the branchial enzyme capacity (compared to basal activity at a set salinity) when temperature is elevated and the scope for temperature adaptation becomes smaller at increasing salinity. Renal Na⁺,K⁺-ATPase capacity appears fixed and activity appears to be determined by temperature.

Seabream Larval Physiology under Ocean Warming and Acidification

The vulnerability of early fish stages represents a critical bottleneck for fish recruitment; therefore, it is essential to understand how climate change affects their physiology for more sustainable management of fisheries. Here, we investigated the effects of warming (OW; +4 °C) and acidification (OA; ΔpH = 0.5) on the heart and oxygen consumption rates, metabolic enzymatic machinery—namely citrate synthase (CS), lactate dehydrogenase (LDH), and ß-hydroxyacyl CoA dehydrogenase (HOAD), of seabream (Sparus aurata) larvae (fifteen days after hatch). Oxygen consumption and heart rates showed a significant increase with rising temperature, but decreased with pCO2. Results revealed a significant increase of LDH activity with OW and a significant decrease of the aerobic potential (CS and HOAD activity) of larvae with OA. In contrast, under OA, the activity levels of the enzyme LDH and the LDH:CS ratio indicated an enhancement of anaerobic pathways. Although such a short-term metabolic strategy may eventually sustain the basic costs of maintenance, it might not be adequate under the future chronic ocean conditions. Given that the potential for adaptation to new forthcoming conditions is yet experimentally unaccounted for this species, future research is essential to accurately predict the physiological performance of this commercially important species under future ocean conditions.

Adaptive responses of fishes to climate change: Feedback between physiology and behaviour

The adaptive capacity of individuals, from their cells to their overall performance, allows species to adjust to environmental change. We assess a hierarchy of responses (from cells to organismal growth and behaviour) to understand the flexibility of adaptive responses to future ocean conditions (warming and acidification) in two species of fish with short lifespans by conducting a long-term mesocosm/aquarium experiment. Fishes were exposed to elevated CO₂ and temperature in a factorial design for a five-month period. We found a feedback mechanism between cellular defence and behavioural responses. In circumstances where their antioxidant defence mechanism was activated (i.e. warming or acidification), increased feeding rates prevented oxidative damage (i.e. during warming Sp. 1). However, when feeding rates failed to increase to provide additional energy needed for antioxidant defence, oxidative damage could not be prevented (warming + acidification Sp. 1). In contrast, when the activation of antioxidant defence was not required, energy intake from increased feeding was redirected to increased fish growth (acidification Sp. 2, warming + acidification Sp. 2), whilst no gain in growth rate was observed where feeding remained unchanged (acidification Sp. 1 or warming Sp. 2). This adaptive strategy seems to rely on the inherent behavioural response of fishes to their environment and such adjustability shows the kind of responses that organisms may express to prevail in future ocean climate. Indeed, assessing the link between responses from cellular to organismal levels, using a diversity of fitness indicators and behaviour, provides a fundamental understanding of how organisms as a whole may adjust to prevail in a future world.

The impact of acute thermal stress on the metabolome of the black rockfish (Sebastes schlegelii)

Acute change in water temperature causes heavy economic losses in the aquaculture industry. The present study investigated the metabolic and molecular effects of acute thermal stress on black rockfish (Sebastes schlegelii). Gas chromatography time-of-flight mass spectrometry (GC-TOF-MS)-based metabolomics was used to investigate the global metabolic response of black rockfish at a high water temperature (27°C), low water temperature (5°C) and normal water temperature (16°C). Metabolites involved in energy metabolism and basic amino acids were significantly increased upon acute exposure to 27°C (P < 0.05), and no change in metabolite levels occurred in the low water temperature group. However, certain fatty acid levels were elevated after cold stress (P < 0.05), and this effect was not observed in the 27°C group, suggesting that acute high and low temperature exposures caused different physiological responses. Using quantitative real-time PCR, we analyzed the expression of ubiquitin (ub), hypoxia-inducible factor (hif), lactate dehydrogenase (ldh), and acetyl-CoA carboxylase (acac). Higher expression levels of ub, hif, and ldh (P < 0.05) were observed in the high water temperature group, but no changes in these expression levels occurred in the low water temperature group. Our findings provide a potential metabolic profile for black rockfish when exposed to acute temperature stress and provide some insights into host metabolic and molecular responses to thermal stress.

Physio-metabolic response of rainbow trout during prolonged food deprivation before slaughter

Fish normally undergo periods of food deprivation that are longer than non-hibernating mammals. In aquacultured rainbow trout (Oncorhynchus mykiss), it is unclear how fasting may affect their physiological adaptative response, especially when they are normally fed daily. In addition, that response may vary with temperature, making it necessary to express fasting duration in terms of degree days. In the current study, trout were fasted for 5, 10, and 20 days (55, 107, and 200 degree days (°C d), respectively). To assess the physiological response of fish to fasting, different biometric, blood, plasma, and metabolic parameters were measured, as well as liver fatty acid composition. The fish weight, condition factor, and the hepato-somatic index of 5-day fasted trout were not significantly different from those of control fish. Gastric pH increased as fasting progressed while plasma concentrations of glucose, triglycerides, and total proteins decreased significantly after 10 days of fasting, while the percentage of non-esterified fatty acids increased. There were no significant differences in plasma ions (sodium, potassium, and calcium), except for chloride ion which decreased after 5 days of fasting. Liver glycogen decreased after 5 days of fasting while glycogen concentration in muscle did not decrease until 20 days of fasting. Liver color presented a higher chroma after 5 days of fasting, suggesting a mobilization of reserves. Finally, acetylcholinesterase activity in the brain was not affected by food deprivation but increased after 10 days of fasting in liver and muscle, suggesting the mobilization of body reserves, but without severely affecting basal metabolism.

Seasonal Changes in Metabolism and Cellular Stress Phenomena in the Gilthead Sea Bream (Sparus aurata)

Seasonal temperature changes may take organisms to the upper and lower limit of their thermal range, with respective variations in their biochemical and metabolic profile. To elucidate these traits, we investigated metabolic and antioxidant patterns in tissues of sea bream Sparus aurata during seasonal acclimatization for 1 yr in the field. Metabolic patterns were assessed by determining lactate dehydrogenase, citrate synthase, and β-hydroxyacyl CoA dehydrogenase activities, their kinetic properties and plasma levels of glucose, lactate, and triglycerides and tissue succinate levels. Oxidative stress was assessed by determining antioxidant enzymes superoxide dismutase, catalase, and glutathione reductase activities and levels of thiobarbituric acid reactive substances. Xanthine oxidase (XO) activity was determined as another source of reactive oxygen species (ROS) production. Furthermore, we studied the antiapoptotic protein indicator Bcl-2 and the apoptotic protein indicators Bax, Bad, ubiquitin, and caspase as well as indexes of autophagy (LC3B II/LC3B I and SQSTM1/p62) in the liver and the heart to identify possible relationships between oxidative stress and cell death. The results indicate clear seasonal metabolic patterns involving oxidative stress during summer as well as winter. During cold acclimatization, lipid oxidation is induced, while during increased temperatures, warm-induced metabolic activation and carbohydrate oxidation are observed. Thus, oxidative stress seems to be more prominent during warming because of the increased aerobic metabolism. The seasonal profile of apoptosis and XO as another source of ROS matches the results obtained in the laboratory and are interpreted within the framework of oxygen- and capacity-limited thermal tolerance.

Come rain or come shine: environmental effects on the infective stages of Sparicotyle chrysophrii, a key pathogen in Mediterranean aquaculture

BACKGROUND

Evidence concerning the environmental influence on monogenean transmission and infection processes is widely accepted, although only the effects of a limited number of abiotic factors on particular monogenean species have been explored. The current context of climate change calls for further research both on this subject, and also that concerning monogenean hosts, especially in aquaculture.

METHODS

In this study, four experiments were used to assess the response of the infective stages of Sparicotyle chrysophrii, a pathogenic monogenean from gilthead sea bream (Sparus aurata) cultures in the Mediterranean, to variations of temperature (from 10 °C to 30 °C), pH (7.0 and 7.9), photoperiod (LD 12:12, LD 0:24 and LD 24:0) and salinity (from 27 ppt to 47 ppt).

RESULTS

Thermal variations cause the strongest responses among the infective stages of S. chrysophrii, which reduced development and survival times as temperature increased. The optimal thermal range for maximum hatching success was found between 14 and 22 °C, whereas temperatures of 10 and 30 °C probably represent biological thermal limits. Reductions of development time and hatching rates were recorded at the lowest pH level, but hatching success remained above 50%, suggesting a certain degree of tolerance to slight pH variations. Photoperiod acts as an environmental cue synchronising the circadian hatching rhythm of S. chrysophrii with the first four hours of darkness. Response to a wide range of salinities was negligible, suggesting a high tolerance to variations of this abiotic factor.

CONCLUSIONS

Larval development and hatching of S. chrysophrii are modulated according to environmental factors, mainly temperature, thus parasite-host coordination and successful infections are enhanced. Therefore, abiotic factors should be broadly considered to design treatments against this monogenean. The high tolerance to the predicted environmental variations over the next century reported for gilthead sea bream and herein exposed for S. chrysophrii suggests that neither will be notably affected by climate change in the western Mediterranean region.

Redox Challenge in a Cultured Temperate Marine Species During Low Temperature and Temperature Recovery

Aquaculture is a growing industry that is increasingly providing a sizable proportion of fishery products for human consumption. Dietary energy and temperature fluctuations affect fish health and may even trigger mortality, causing great losses in fish production during winter. To better understand this unproductive winter period in aquaculture, the redox status in a cultured marine species, the gilthead sea bream, was analyzed for the first time by inducing controlled temperature fluctuations and reducing dietary lipid content. Two groups of fish (by triplicate), differing in their dietary lipid content (18% vs. 14%), were subjected to 30 days at 22°C (Pre-Cold), 50 days at 14°C (Cold) and then 35 days at 22°C (Recovery). Plasma and liver redox metabolites (oxidized lipid, oxidized protein and thiol groups), liver glutathione forms (total, oxidized and reduced) and liver antioxidant enzyme activities were measured. Reducing dietary lipid content did not affect gilthead sea bream growth, glutathione levels or enzyme activities, but did reduce the amount of oxidized lipids. A sustained low temperature of 14°C showed a lack of adaptation of antioxidant enzyme activities, mainly catalase and glutathione reductase, which subsequently affected the glutathione redox cycle and caused an acute reduction in total hepatic glutathione levels, irrespective of diet. Antioxidant enzyme activities were gradually restored to their pre-cold levels, but the glutathione redox cycle was not restored to its pre-cold values during the recovery period used. Moreover, the lower lipid diet was associated with transiently increased liver oxidized protein levels. Thus, we propose that fish should be fed a low lipid diet during pre-cold and cold periods, which would reduce oxidized lipid levels without affecting fish growth, and a higher energy diet during the recovery period. Moreover, diets supplemented with antioxidants should be considered, especially during temperature recovery.

Somatotropic Axis Regulation Unravels the Differential Effects of Nutritional and Environmental Factors in Growth Performance of Marine Farmed Fishes

The Gh/Prl/Sl family has evolved differentially through evolution, resulting in varying relationships between the somatotropic axis and growth rates within and across fish species. This is due to a wide range of endogenous and exogenous factors that make this association variable throughout season and life cycle, and the present minireview aims to better define the nutritional and environmental regulation of the endocrine growth cascade over precisely defined groups of fishes, focusing on Mediterranean farmed fishes. As a result, circulating Gh and Igf-i are revitalized as reliable growth markers, with a close association with growth rates of gilthead sea bream juveniles with deficiency signs in both macro- or micro-nutrients. This, together with other regulated responses, promotes the use of Gh and Igf-i as key performance indicators of growth, aerobic scope, and nutritional condition in gilthead sea bream. Moreover, the sirtuin-energy sensors might modulate the growth-promoting action of somatotropic axis. In this scenario, transcripts of igf-i and gh receptors mirror changes in plasma Gh and Igf-i levels, with the ghr-i/ghr-ii expression ratio mostly unaltered over season. However, this ratio is nutritionally regulated, and enriched plant-based diets or diets with specific nutrient deficiencies downregulate hepatic ghr-i, decreasing the ghr-i/ghr-ii ratio. The same trend, due to a ghr-ii increase, is found in skeletal muscle, whereas impaired growth during overwintering is related to increase in the ghr-i/ghr-ii and igf-ii/igf-i ratios in liver and skeletal muscle, respectively. Overall, expression of insulin receptors and igf receptors is less regulated, though the expression quotient is especially high in the liver and muscle of sea bream. Nutritional and environmental regulation of the full Igf binding protein 1-6 repertoire remains to be understood. However, tissue-specific expression profiling highlights an enhanced and nutritionally regulated expression of the igfbp-1/-2/-4 clade in liver, whereas the igfbp-3/-5/-6 clade is overexpressed and regulated in skeletal muscle. The somatotropic axis is, therefore, highly informative of a wide-range of growth-disturbing and stressful stimuli, and multivariate analysis supports its use as a reliable toolset for the assessment of growth potentiality and nutrient deficiencies and requirements, especially in combination with selected panels of other nutritionally regulated metabolic biomarkers.

The expression pattern of hsp70 plays a critical role in thermal tolerance of marine demersal fish: Multilevel responses of Paralichthys olivaceus and its hybrids (P. olivaceus ♀ × P. dentatus ♂) to chronic and acute heat stress

Ocean warming has multifaceted impacts on marine organisms. This study investigated the different responses of Paralichthys olivaceus and the hybrids (P. olivaceus ♀ × P. dentatus ♂) to chronic and acute heat stress. By comparing their survival, behavioural and histological changes, we found that the hybrids possess a better thermal tolerance with a higher cumulative survival rate (CSR), relatively fewer behavioural changes and less gill damage. Moreover, we analysed the relationship between thermal tolerance and the hsp70 expression pattern and found that thermal tolerant species (the hybrids) exhibited higher threshold induction temperature, shorter durations, stronger magnitudes and a delay in hsp70 expression. We speculated that the expression mode of hsp70, rather than itself, plays a critical role in thermal tolerance. These findings would improve the understanding of hsp70 in future marine climate research and help clarify the profound effects of rising temperature on marine demersal fishes.

Contrasting impacts of ocean acidification and warming on the molecular responses of CO2-resilient oysters

BACKGROUND

This study characterises the molecular processes altered by both elevated CO₂ and increasing temperature in oysters. Differences in resilience of marine organisms against the environmental stressors associated with climate change will have significant implications for the sustainability of coastal ecosystems worldwide. Some evidence suggests that climate change resilience can differ between populations within a species. B2 oysters represent a unique genetic resource because of their capacity to better withstand the impacts of elevated CO₂ at the physiological level, compared to non-selected oysters from the same species (Saccostrea glomerata). Here, we used proteomic and transcriptomic analysis of gill tissue to evaluate whether the differential response of B2 oysters to elevated CO₂ also extends to increased temperature.

RESULTS

Substantial and distinctive effects on protein concentrations and gene expression were evident among B2 oysters responding to elevated CO₂ or elevated temperature. The combination of both stressors also altered oyster gill proteomes and gene expression. However, the impacts of elevated CO₂ and temperature were not additive or synergistic, and may be antagonistic.

CONCLUSIONS

The data suggest that the simultaneous exposure of CO₂-resilient oysters to near-future projected ocean pH and temperature results in complex changes in molecular processes in order to prevent stress-induced cellular damage. The differential response of B2 oysters to the combined stressors also indicates that the addition of thermal stress may impair the resilience of these oysters to decreased pH. Overall, this study reveals the intracellular mechanisms that might enable marine calcifiers to endure the emergent, adverse seawater conditions resulting from climate change.

Multiple Stressors in a Changing World: The Need for an Improved Perspective on Physiological Responses to the Dynamic Marine Environment

Abiotic conditions (e.g., temperature and pH) fluctuate through time in most marine environments, sometimes passing intensity thresholds that induce physiological stress. Depending on habitat and season, the peak intensity of different abiotic stressors can occur in or out of phase with one another. Thus, some organisms are exposed to multiple stressors simultaneously, whereas others experience them sequentially. Understanding these physicochemical dynamics is critical because how organisms respond to multiple stressors depends on the magnitude and relative timing of each stressor. Here, we first discuss broad patterns of covariation between stressors in marine systems at various temporal scales. We then describe how these dynamics will influence physiological responses to multi-stressor exposures. Finally, we summarize how multi-stressor effects are currently assessed. We find that multi-stressor experiments have rarely incorporated naturalistic physicochemical variation into their designs, and emphasize the importance of doing so to make ecologically relevant inferences about physiological responses to global change.