Oxidative stress and biomarker responses in the Atlantic halibut after long term exposure to elevated CO2 and a range of temperatures

Do predator (Mystus gulio) and prey (Penaeus monodon) have differential response against heatwaves? Unveiling through oxidative stress biomarkers and thermal tolerance estimation

Extreme climatic events such as heatwaves are anticipated to intensify in future and impose additional thermal stress to aquatic animals. Knowledge regarding an organism's thermal tolerance or sensitivity is therefore important in determining the effects of fluctuating water temperature on physiological responses. Thus, thermal tolerance tests can serve as a first step in understanding the present and future effects of climate warming. Climatic variability will alter prey-predator attributes differentially and impact their subsequent interactions. The key objective of this study was to compare and decode the stress responses, resistance and vulnerability of two economically important species from Sundarbans estuarine system- Penaeus monodon (prey) and Mystus gulio (predator) subjected to acute thermal challenges such as sudden heatwaves. Both the species were subjected to an increasing thermal ramp of 1°C h^-1 from 22°C to 42°C. Organisms were observed continuously throughout the ramping period and changes in the locomotory behaviour were followed until their loss of equilibrium. The digestive tissue samples were dissected out from both M. gulio and P. monodon at every 2°C and also after a recovery period of 48 h. The SOD, CAT, GST, LPO were measured and integrated biomarker response (IBR) was analysed. The results from thermal tolerance maxima estimation, biomarker study, IBR responses indicated more intense stress response in fish M. gulio whereas recovery potential was greater in shrimp P. monodon. Our findings corroborate the 'trophic sensitivity hypothesis' which advocates predators to be less tolerant in aggravated environmental stress than their prey.

pCO2-driven seawater acidification affects aqueous-phase copper toxicity in juvenile flounder Paralichthys olivaceus: Metal accumulation, antioxidant defenses and detoxification in livers

Ocean acidification potentially influences the biotoxicity of metals and the antioxidant defense systems of marine organisms. This study investigated how pCO₂-driven seawater acidification (SA) affected aqueous-phase copper (Cu) toxicity in the juvenile flounder Paralichthys olivaceus from the perspective of hepatic oxidative stress and damage to better understand the mechanisms underlying the biological effects produced by the two stressors. Fish were exposed to aqueous-phase Cu at relevant ambient and polluted concentrations (0, 5, 10, 50, 100 and 200 μg L^-1) at different pH levels (no SA: pH 8.10; moderate SA: pH 7.70, pCO₂ ∼1353.89 μatm; extreme SA: pH 7.30, pCO₂ ∼3471.27 μatm) for 28 days. A battery of biomarkers in the livers was examined to investigate their roles in antioxidant defense and detoxification in response to coexposure. Hepatic Cu accumulation (30.22-184.90 mg kg^-1) was positively correlated with Cu concentrations. The biomarkers responded adaptively to different redox states following SA and Cu exposure. In unacidified seawater, increases in Cu concentrations significantly induced hepatic lipid peroxidation (LPO, by up to 27.03 %), although compensatory responses in antioxidant defenses and detoxification were activated. Moderate SA helped maintain hepatic redox homeostasis and alleviated LPO through different defense strategies, depending on Cu concentrations. Under extreme SA, antioxidant-based defenses were activated to cope with oxidative stress at ambient-low Cu concentrations but failed to defend against Cu toxicity at polluted Cu levels, and LPO (by up to 63.90 %) was significantly induced. Additionally, thiols (GSH and MT) responded actively to cope with Cu toxicity under SA. SOD, CAT, EROD, and GST were also sensitively involved in defending against hepatic oxidative stress during coexposure. These findings highlight the notable interactive effects of SA and Cu and provide a basis for understanding antioxidant-based defenses in marine fish confronting environmental challenges.

Ocean acidification and seasonal temperature extremes combine to impair the thermal physiology of a sub-Antarctic fish

To predict the potential impacts of climate change on marine organisms, it is critical to understand how multiple stressors constrain the physiology and distribution of species. We evaluated the effects of seasonal changes in seawater temperature and near-future ocean acidification (OA) on organismal and sub-organismal traits associated with the thermal performance of Eleginops maclovinus, a sub-Antarctic notothenioid species with economic importance to sport and artisanal fisheries in southern South America. Juveniles were exposed to mean winter and summer sea surface temperatures (4 and 10 °C) at present-day and near-future pCO₂ levels (~500 and 1800 μatm). After a month, the Critical Thermal maximum and minimum (CTmax, CTmin) of fish were measured using the Critical Thermal Methodology and the aerobic scope of fish was measured based on the difference between their maximal and standard rates determined from intermittent flow respirometry. Lipid peroxidation and the antioxidant capacity were also quantified to estimate the oxidative damage potentially caused to gill and liver tissue. Although CTmax and CTmin were higher in individuals acclimated to summer versus winter temperatures, the increase in CTmax was minimal in juveniles exposed to the near-future compared to present-day pCO₂ levels (there was a significant interaction between temperature and pCO₂ on CTmax). The reduction in the thermal tolerance range under summer temperatures and near-future OA conditions was associated with a reduction in the aerobic scope observed at the elevated pCO₂ level. Moreover, an oxidative stress condition was detected in the gill and liver tissues. Thus, chronic exposure to OA and the current summer temperatures pose limits to the thermal performance of juvenile E. maclovinus at the organismal and sub-organismal levels, making this species vulnerable to projected climate-driven warming.

The effect of environmental stressors on growth in fish and its endocrine control

Fish body growth is a trait of major importance for individual survival and reproduction. It has implications in population, ecology, and evolution. Somatic growth is controlled by the GH/IGF endocrine axis and is influenced by nutrition, feeding, and reproductive-regulating hormones as well as abiotic factors such as temperature, oxygen levels, and salinity. Global climate change and anthropogenic pollutants will modify environmental conditions affecting directly or indirectly fish growth performance. In the present review, we offer an overview of somatic growth and its interplay with the feeding regulatory axis and summarize the effects of global warming and the main anthropogenic pollutants on these endocrine axes.

Early Exposure to Environmental Pollutants: Imidacloprid Potentiates Cadmium Toxicity on Zebrafish Retinal Cells Death

In the present study, we analyzed the combination of non-toxic concentrations per se, of Cd and a pesticide the imidacloprid (IMI) (10 and 50 μM for Cd and 195 μM for IMI), to highlight early developmental toxicity and possible damage to retinal cells. Co-exposure to Cd and IMI showed a toxic effect in zebrafish larval development, with lowered degrees of survival and hatching, and in some cases the induction of structural alterations and edema. In addition, co-exposure to 50 and 195 μM, respectively, for Cd and IMI, also showed increased apoptosis in eye cells, accompanied by up regulation of genes associated with antioxidant markers (cat, sod1, nrf2 and ho-1). Thus, the present study aims to highlight how the presence of multiple contaminants, even at low concentrations, can be a risk factor in a model of zebrafish (Danio rerio). The presence of other contaminants, such as IMI, can cause an enhancement of the toxic action of Cd on morphological changes in the early life stage of zebrafish, but more importantly disrupt the normal development of the retina, eventually triggering apoptosis.

The effects of low pH and high water temperature on oxidative stress and cell damage in juvenile olive flounder Paralichthys olivaceus: comparison of single and combined environmental conditions

The use of fossil fuels by anthropogenic activities causes ocean acidification and warming, and these changes in the marine environment can negatively affect the metabolism, growth, and survival of fish. In the present study, we evaluated the ability of olive flounder Paralichthys olivaceus to cope with future marine environmental changes by investigating the oxidative stress (cortisol, HSP70), antioxidant enzyme (superoxide dismutase; SOD, catalase; CAT) activity, and apoptosis (caspase-3) after exposure to control conditions (20 °C and pH 8.1), warming (30 °C) and acidification (pH 7.5) conditions, and a combined environment (30 °C and pH 7.5) for 28 days. Under warming conditions, increased oxidative stress, activity of antioxidant enzymes, and apoptosis were observed. Acidifying conditions showed negative effects at the beginning of exposure, but these effects were offset over time. Even in a combined environment of acidification and warming, negative effects were seen only at the beginning of exposure and were not sustained. In conclusion, the effects of acidification on oxidative stress, antioxidant response, and apoptosis in P. olivaceus did not exceed the effects of warming. These results suggest that P. olivaceus can cope with the predicted future acidifying environment.

Combined effects of ocean warming and acidification on marine fish and shellfish: A molecule to ecosystem perspective

It is expected that by 2050 human population will exceed nine billion leading to increased pressure on marine ecosystems. Therefore, it is conjectured various levels of ecosystem functioning starting from individual to population-level, species distribution, food webs and trophic interaction dynamics will be severely jeopardized in coming decades. Ocean warming and acidification are two prime threats to marine biota, yet studies about their cumulative effect on marine fish and shellfishes are still in its infancy. This review assesses existing information regarding the interactive effects of global environmental factors like warming and acidification in the perspective of marine capture fisheries and aquaculture industry. As climate change continues, distribution pattern of species is likely to be altered which will impact fisheries and fishing patterns. Our work is an attempt to compile the existing literatures in the biological perspective of the above-mentioned stressors and accentuate a clear outline of knowledge in this subject. We reviewed studies deciphering the biological consequences of warming and acidification on fish and shellfishes in the light of a molecule to ecosystem perspective. Here, for the first time impacts of these two global environmental drivers are discussed in a holistic manner taking into account growth, survival, behavioural response, prey predator dynamics, calcification, biomineralization, reproduction, physiology, thermal tolerance, molecular level responses as well as immune system and disease susceptibility. We suggest urgent focus on more robust, long term, comprehensive and ecologically realistic studies that will significantly contribute to the understanding of organism's response to climate change for sustainable capture fisheries and aquaculture.

Effects of Different Temperatures on the Antibacterial, Immune and Growth Performance of Crucian Carp Epidermal Mucus

Fish is one of the important sources of energy and protein, and proper water temperature is key to successful fish breeding. The authors of this study evaluated crucian carp growth, mucus antibacterial properties, and immune indicators at 17, 21, 24, 27, and 31 °C. The results indicated that in the range of 17–31 °C, the resistance of epidermal mucus to Vibrio harveyi decreased with temperature rising. At 24 and 27 °C, the activities of lysozyme and catalase significantly increased; alkaline phosphatase activity, superoxide dismutase activity, and total protein concentration first increased and then decreased with rising temperature; the highest values were observed at 24 °C, with increases of 56.55%, 26.64%, and 44.52%, respectively, compared to those under the 17 °C treatment. When the treatment reached 27 °C, the temperature had an effect on the growth and antibacterial properties of crucian carp, and the activities of alkaline phosphatase and superoxide dismutase were significantly reduced. At temperatures of 17–24 °C, the survival rate of crucian carp could reach more than 93%, and at the temperature of 24 °C, the specific growth rate reached the highest value of 43.29%. Therefore, the most favorable temperature for the long-term breeding of crucian carp was found to be 24 °C. This study provides a favorable experimental basis for the establishment of intelligent aquaculture systems and the setting of water environment parameters.

Does acidification lead to impairments on oxidative status and survival of orange clownfish Amphiprion percula juveniles?

The nitrification process in recirculating aquaculture systems can reduce water pH. Fish can also be exposed to water acidification during transport, an important feature in the aquarium industry, as live fish can be kept in a closed environment for more than 24 h during overseas aerial transportation. Therefore, it is important to study the responses of fish to acidic environments. We investigated the impacts of acute exposure to decreasing pH levels in orange clownfish Amphiprion percula juveniles on their survival and oxidative stress status. Fish were exposed to pH 5, 6, 7, and 8 for 96 h. We observed a significant reduction in survival (85%) and protein damage as measured by P-SH (protein thiol) for fish maintained at pH 5. Despite no effects on survival or oxidative damage, fish exposed to pH 6 showed an increase in their antioxidant defense systems, demonstrating this pH level could not be suitable for them as well. Furthermore, there were no negative effects for fish kept at pH 7, compared to those maintained at pH 8 during this short-term evaluation.

Primary, secondary, and tertiary stress responses of juvenile seahorse Hippocampus reidi exposed to acute acid stress in brackish and seawater

Seahorse Hippocampus reidi is a vulnerable species, inhabiting estuarine and coastal waters. The safety of acidic environments for fish has been considered in terms of ocean acidification in nature and decreasing pH in intensive aquaculture systems. This study aimed to investigate the effects of acute exposition (96 h) of juvenile seahorses to different pH (5, 6, 7, and 8) in brackish (BW - salinity 11) or seawater (SW - salinity 33). For that, we studied the responses of cortisol, oxidative stress, and survival, thus covering primary, secondary, and tertiary stress responses. In SW, cortisol levels were not altered for fish maintained at pH 5 and 8. However, in BW, cortisol was higher for fish kept at pH 5. Regarding secondary stress responses, only GST activity increased with acidification in SW. However, acidification in BW caused biochemical alterations at enzymatic level (SOD, GST, GPx) and glutathione metabolism, accompanied by reduction of antioxidant capacity (TEAC) and increased lipid peroxidation (TBARS). Survival was always above 90% and it did not differ significantly among pH levels. Our results suggest that H. reidi juveniles are more vulnerable to acidic exposure in BW than in SW.

NOD-like receptor signaling pathway activation: A potential mechanism underlying negative effects of benzo(α)pyrene on zebrafish

Benzo(α)pyrene (BaP) is one of typical polycyclic aromatic hydrocarbons (PAHs) in aquatic environments and has been shown to cause toxic effects to aquatic animals. Although the negative effects of BaP have been investigated, the potential toxic mechanisms remain uncharacterized. To explore the potential mechanisms mediating the toxic effects of BaP, zebrafish (Danio rerio) were exposed to BaP for 15 days and the toxic effects of BaP in zebrafish liver were investigated using physiological and transcriptomic analyses. After 15-day BaP exposure, zebrafish liver exhibited abnormalities including increased cytoplasmic vacuolation, inflammatory cell infiltration, swelled nuclei and irregular pigmentation. BaP exposure also induced oxidative stress to the liver of zebrafish. Transcriptomic profiles revealed 5129 differentially expressed genes (DEGs) after 15-days of BaP exposure, and the vast majority of DEGs were up-regulated under BaP treatment. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses suggest that genes related to immune response were significantly dysregulated. Furthermore, the nucleotide-binding, oligomerization domain (NOD)-like receptor signaling pathway was significantly enriched and most of the genes in this pathway exhibited enhanced expression after BaP exposure. These results partially explained the mechanisms underlying the toxic effects of BaP on zebrafish liver. In conclusion, BaP has the potential to induce physiological responses in zebrafish liver through altering associated genes.

Antioxidant responses of triangle sail mussel Hyriopsis cumingii exposed to toxic Microcystis aeruginosa and thermal stress

Harmful algal blooms (HABs) and thermal stress as climate changes become more common in global water ecosystem, especially under eutrophic habitats. Here our study examined the combined impacts of bloom forming cyanobacteria Microcystis aeruginosa and thermal stress on the antioxidant responses of the ecologically important species triangle sail mussel Hyriopsis cumingii. The differential responses of a series of enzymes, e.g. superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione-S-transferase (GST), as well as signal metabolites including reactive oxygen species (ROS), malondialdehyde (MDA) and glutathione (GSH) involved in antioxidant defense mechanisms were analyzed during 14 d exposure to toxic cyanobacterium M. aeruginosa and 7 d depuration period. The activities of SOD and GPx as well as the content of ROS and MDA in H. cumingii increased, while CAT activity reduced due to M. aeruginosa exposure. Thermal stress resulted in decrease of CAT, the accumulation of GSH and the enhance of GST and SOD. Meanwhile, the interactive effects among M. aeruginosa, thermal stress and time were also observed on most parameters except for GST activity. The total amount of microcystins (MC) in sail mussels increased with concentrations of exposed M. aeruginosa, independently of the presence or absence of thermal stress. Although around 50% of MC in mussels dropped in the depuration period, most parameters showed alterations because of cyanobacteria exposure and thermal stress. Overall, these findings suggested that toxic cyanobacteria or thermal stress induces oxidative stress and severely affects the enzymes activities and intermediates level associated with antioxidant defense mechanisms in sail mussels respectively. More importantly, the toxic impacts on sail mussels could be intensified by their combination.

Effects of pollution on marine organisms

This review covers selected 2019 articles on the biological effects of pollutants, including human physical disturbances, on marine and estuarine plants, animals, ecosystems, and habitats. The review, based largely on journal articles, covers field, and laboratory measurement activities (bioaccumulation of contaminants, field assessment surveys, toxicity testing, and biomarkers) as well as pollution issues of current interest including endocrine disrupters, emerging contaminants, wastewater discharges, marine debris, dredging, and disposal. Special emphasis is placed on effects of oil spills and marine debris due largely to the 2010 Deepwater Horizon oil blowout in the Gulf of Mexico and proliferation of data on the assimilation and effects of marine debris microparticulates. Several topical areas reviewed in the past (e.g., mass mortalities ocean acidification) were dropped this year. The focus of this review is on effects, not on pollutant sources, chemistry, fate, or transport. There is considerable overlap across subject areas (e.g., some bioaccumulation data may be appeared in other topical categories such as effects of wastewater discharges, or biomarker studies appearing in oil toxicity literature). Therefore, we strongly urge readers to use keyword searching of the text and references to locate related but distributed information. Although nearly 400 papers are cited, these now represent a fraction of the literature on these subjects. Use this review mainly as a starting point. And please consult the original papers before citing them.

Effects of combined stressors to cadmium and high temperature on antioxidant defense, apoptotic cell death, and DNA methylation in zebrafish (Danio rerio) embryos

Fish are frequently affected by environmental stressors, such as temperature changes and heavy metal exposure, in aquatic ecosystems. In this study, we evaluated the combined effects of cadmium (Cd) toxicity and temperature (rearing temperature of 26 °C and heat stress at 34 °C) on zebrafish (Danio rerio) embryos. The survival and heart rates of zebrafish embryos decreased at relatively high Cd concentrations of 0.07 and 0.1 mg L^-1. Abnormal morphology was induced by exposure to a combination of Cd toxicity and heat stress. The yolk sac edema size was not significantly different between the control- and Cd-treated groups. Cd exposure induced reactive oxygen species (ROS) production and cell death in the live zebrafish. High temperature (34 °C) triggered Cd-induced cell death and intracellular ROS production to a greater extent than the rearing temperature of 26 °C. Transcriptional levels of six genes-CAT, SOD, p53, BAX, Dnmt1, and Dnmt3b-were investigated. The mRNA expression of CAT and SOD, molecular indicators of oxidative stress, was increased significantly at 34 °C after Cd exposure. The mRNA expression of CAT was more sensitive to temperature than that of SOD in Cd-treated zebrafish. p53 and BAX, apoptosis-related genes, were upregulated upon combined exposure to high temperature and Cd. In addition, at 34 °C, the expression of Dnmt1 and Dnmt3b transcripts, markers of DNA methylation, was increased upon exposure of zebrafish to all concentrations of Cd. Overall, these results suggest that high temperature facilitates the potential role of Cd toxicity in the transcriptional regulation of genes involved in the antioxidant system, apoptosis, and DNA methylation.