Physiological Mechanisms of Acute Upper Thermal Tolerance in Fish.

This review is focused on the questions of why fish exhibit heat failure at thermal extremes and which physiological mechanisms determine the acute upper thermal tolerance. We propose that rapid direct thermal impacts on fish act through three fundamental molecular mechanisms reaction rates, protein structure, and membrane fluidity. During acute warming, these molecular effects then lead to loss of equilibrium and death through various cellular, organ, and physiological pathways. These pathways include mitochondrial dysfunction, oxygen limitation, and impacted excitability of excitable cells and eventually lead to neural and/or muscular failure. The pathways may also lead to loss of homeostasis and subsequent heat failure. There is strong evidence in some species for oxygen limitation in these processes and strong evidence against it in other species and contexts. The limiting mechanisms during acute warming therefore appear to differ between species, life stages, and recent thermal history. We conclude that a single mechanism underpinning the acute upper thermal tolerance across species and contexts will not be found. Therefore, we propose future avenues of research that can elucidate major patterns of physiological thermal limitations in fish.

Establishment of a cobia (Rachycentron canadum) gill cell line: A valuable tool for immune response studies.

Cobia (Rachycentron canadum), a commercially important marine fish, has been used to develop a novel gill cell line, designated CG, for the first time. The CG cell line was cultured in Leibovitz's-15 medium with 5% fetal bovine serum (FBS) and successfully sub-cultured more than 110 passages. It underwent verification through sequencing of the mitochondrial cytochrome C oxidase subunit I (COI) gene. Optimal growth rate was achieved when the CG cell line was cultured in a medium supplemented with 5% FBS, 1% Penicillin-Streptomycin (P/S), and 5 parts per thousand (ppt) of coral sea salt water, maintained at a temperature of 27 °C. The addition of 5 ppt of salt in the growth medium suggests that this cell line could be a viable in vitro tool for marine ecosystem toxicological studies or for culturing marine parasitic microorganisms. The CG cell line was also successfully transfected using the pTurbo-GFP plasmids, showing an 18% efficiency, with observable GFP expression. Furthermore, the cell line has been effectively cryopreserved. Gene expression analysis indicated that the CG cell line exhibits responsive regulation of immune gene expression when exposured to various stimulants, highlighting its potential as an in vitro platform for immune response studies. This makes it suitable for exploring dynamic immune signaling pathways and host-pathogen interactions, thereby offering valuable insights for therapeutic development.

Molecular cloning and functional characterization of mitochondrial RNA splicing 2 in fish Megalobrama amblycephala, and its potential roles in magnesium homeostasis and mitochondrial function.

Mitochondrial function can be regulated by ion channels. Mitochondrial RNA splicing 2 (Mrs2) is a magnesium ion (Mg2+) channel located in the inner mitochondrial membrane, thereby mediating the Mg2+ influx into the mitochondrial matrix. However, its potential role in regulating the Mg homeostasis and mitochondrial function in aquatic species is still unclear. This study molecularly characterizes the gene encoding Mrs2 in fish M. amblycephala with its functions in maintaining the Mg homeostasis and mitochondrial function verified. The mrs2 gene is 2133 bp long incorporating a 1269 bp open reading frame, which encodes 422 amino acids. The Mrs2 protein includes two transmembrane domains and a conserved tripeptide Gly-Met-Asn, and has a high homology (65.92-97.64%) with those of most vertebrates. The transcript of mrs2 was relatively high in the white muscle, liver and kidney. The inhibition of mrs2 reduces the expressions of Mg2+ influx/efflux-related proteins, mitochondrial Mg content, and the activities of mitochondrial complex I and V in hepatocytes. However, the over-expression of mrs2 increases the expressions of Mg2+ influx/efflux-related proteins, mitochondrial Mg content, and the complex V activity, but decreases the activities of mitochondrial complex III and IV and citrate synthase in hepatocytes. Collectively, Mrs2 is highly conserved among different species, and is prerequisite for maintaining Mg homeostasis and mitochondrial function in fish.

Effect of different temperature variations on the physiological state of catfish species: a systematic review.

Catfish are a highly diverse group of fish that are found in various regions across the globe. The significance of catfish culture extends to various aspects, including food security, economic advancement, preservation of cultural legacy, and ecological stewardship. The catfish industry is presently encountering unprecedented challenges as a consequence of the variability in water temperature caused by climate change. Temperature is a significant abiotic component that regulates and restricts fish physiology throughout their life cycle. The impact of severe temperatures on various species of catfish is dependent upon the magnitude of the stressor and additional influencing factors. This paper presents an analysis of the effects of temperature fluctuations on various aspects of catfish species, including growth and survival, blood parameters, enzymatic and hormone response, oxygen consumption rates, sound generation and hearing skills, nutritional requirements, and other phenotypic attributes. While this review is certainly not exhaustive, it offers a broad synopsis of the ideal temperature ranges that are most favorable for several catfish species. In-depth research to investigate the interacting impacts of severe temperature occurrences in conjunction with other associated environmental stresses on a wider variety of catfish species is crucial in order to further our understanding of how catfish species will respond to the anticipated climate change in the future.

Nile tilapia and gilthead seabream dietary self-selection of alternative feeds.

Classical assessments of new fish feeds are anthropocentric, focusing mainly on growth. Although this methodology is accurate, it does not consider the fish' perspective. This study aimed to investigate the behavioural responses and feed preferences of Nile tilapia (Oreochromis niloticus) and gilthead seabream (Sparus aurata) through a self-selection trial using self-feeders. Both species were offered three feeds: a control (PD) commercial-like feed and two diets (ORG1 and ORG2) formulated with different inclusions of alternative ingredients to address some of the current environmental concerns and/or ethical issues often associated with commercial formulations. Three groups of tilapia with an average weight of 163.0 g ± 4.3 g (mean ± SD) and four groups of seabreams with 174.7 g ± 27.0 g were tested. Tilapia exhibited a preference for ORG2 (46.5%), influenced by the sensory properties of the feed and post-ingestion signals. Seabream did not show a preference for any feed. These findings highlight the effectiveness of self-selection experiments in allowing fish to express their feeding behaviour and preferences. Therefore, this approach should be considered in the initial screening and design of new aquaculture feeds and ingredients.

Brewer's spent yeast replacement in carp diet leads to muscle biomass production, recycling, waste management and resource conservation.

Brewer's spent yeast (BSY) is among the most voluminous by-products generated in brewery industry that adds to the waste; however, smart utilization of BSY could lead to edible biomass production besides waste management. To utilize it for biomass production, it is being used in fish feeds; however, its effect on the fish physiology has been scantily studied. The present study investigated the proteomic changes in muscle tissues of carp Labeo rohita fed with BSY-based diet, to understand its impact on muscle physiology and biomass. Six feeds were prepared with different grades of BSY (0, 20, 30, 40, 50, 100% replacement of fishmeal with BSY) and fishes were fed for 90 days. Highest weight gain%, feed conversion efficiency, specific growth rate% were observed in 30% BSY-replaced group and this group was considered for the proteomic study. Comparative shotgun proteomic analysis was carried out by LC-MS/MS and data generated have been deposited in ProteomeXchange Consortium with dataset identifier PXD020093. A total of 62 proteins showed differential abundance; 29 increased and 33 decreased in the 30% BSY-replaced group. Pathway analysis using IPA and Panther tools revealed that the proteins tyrosine protein kinase, PDGFα, PKRCB and Collagen promote muscle growth by inducing the PI3K-AKT pathway. Conversely, the proteins Serine/threonine-protein phosphatase, Phosphatidylinositol 3,4,5-trisphosphate5-phosphatase 2A and Ras-specific guanine- nucleotide-releasing factor inhibit muscle growth indicating that 30% BSY-replaced feed promote muscle growth in a highly controlled manner. Findings suggest that BSY could be recycled for carp feed production in large scale thereby leading to resource conservation, reducing environmental effects.

Dietary supplementation with nerolidol improves the antioxidant capacity and muscle fatty acid profile of Brycon amazonicus exposed to acute heat stress.

An increase in water temperature in the Amazon River has elicited concerns about commercially important fish species associated with food security, such as matrinxã (Brycon amazonicus). Studies have demonstrated the positive effects of diets supplemented with plant-based products that combat heat stress-induced oxidative damage. The aim of this study was to determine whether dietary supplementation with nerolidol prevents or reduces muscle oxidative damage and impairment of the fillet fatty acid profile of matrinxã exposed to heat stress. Plasma and muscle reactive oxygen species (ROS) and lipid peroxidation (LPO) levels were significantly higher in fish exposed to heat stress compared to fish not exposed to heat stress, while plasma superoxide dismutase (SOD) and glutathione peroxidase (GPx) activity was significantly lower. The total content of saturated fatty acids (SFA) in fillets was significantly higher in fish exposed to heat stress compared to fish not exposed to heat stress, while he total content of polyunsaturated fatty acids (PUFA) was significantly lower. Nerolidol prevented the increase of muscle LPO and plasma ROS and LPO levels in fish exposed to heat stress, and partially prevented the increase in muscle ROS levels. Diets containing nerolidol prevented the inhibition of muscle GPx activity in fish exposed to heat stress, and partially prevented the decrease of plasma GPx activity. The nerolidol-supplemented diet prevented the increase of fillet SFA in fish exposed to heat stress, while partially preventing the decrease of PUFA. We conclude that acute heat stress at 34 °C for 72 h causes plasma and muscular oxidative damage, and that homeoviscous adaptation to maintain membrane fluidity can represent a negative impact for fish consumers. A nerolidol diet can be considered a strategy to prevent heat stress-induced oxidative damage and impairment of muscle fatty acid profiles.

Rainbow Trout (Oncorhynchus mykiss) Na+/H+ Exchangers tNhe3a and tNhe3b Display Unique Inhibitory Profiles Dissimilar from Mammalian NHE Isoforms.

Freshwater fishes maintain an internal osmolality of ~300 mOsm, while living in dilute environments ranging from 0 to 50 mOsm. This osmotic challenge is met at least partially, by Na+/H+ exchangers (NHE) of fish gill and kidney. In this study, we cloned, expressed, and pharmacologically characterized fish-specific Nhes of the commercially important species Oncorhynchus mykiss. Trout (t) Nhe3a and Nhe3b isoforms from gill and kidney were expressed and characterized in an NHE-deficient cell line. Western blotting and immunocytochemistry confirmed stable expression of the tagged trout tNhe proteins. To measure NHE activity, a transient acid load was induced in trout tNhe expressing cells and intracellular pH was measured. Both isoforms demonstrated significant activity and recovered from an acute acid load. The effect of the NHE transport inhibitors amiloride, EIPA (5-(N-ethyl-N-isopropyl)-amiloride), phenamil, and DAPI was examined. tNhe3a was inhibited in a dose-dependent manner by amiloride and EIPA and tNhe3a was more sensitive to amiloride than EIPA, unlike mammalian NHE1. tNhe3b was inhibited by high concentrations of amiloride, while even in the presence of high concentrations of EIPA (500 µM), some activity of tNhe3b remained. Phenamil and DAPI were ineffective at inhibiting tNhe activity of either isoform. The current study aids in understanding the pharmacology of fish ion transporters. Both isoforms display inhibitory profiles uniquely different from mammalian NHEs and show resistance to inhibition. Our study allows for more direct interpretation of past, present, and future fish-specific sodium transport studies, with less reliance on mammalian NHE data for interpretation.

The physiological ups and downs of thermal variability in temperate freshwater ecosystems.

Freshwater fish face a variety of spatiotemporal thermal challenges throughout their life. On a broad scale, temperature is an important driver of physiological, behavioural and ecological patterns and ultimately affects populations and overall distribution. These broad patterns are partly underpinned by the small-scale local effects of temperature on individuals within the population. Climate change is increasing the range of daily thermal variation in most freshwater ecosystems, altering behaviour and performance of resident fishes. The aim of this review is understanding how daily thermal variation in temperate rivers affects individual fish physiology, behaviour and overall performance. The following are highlighted in this study: (a) the physical characteristics of rivers that can either buffer or exacerbate thermal variability, (b) the effects of thermal variability on growth and metabolism, (c) the approaches for quantifying thermal variation and thermal stress and (d) how fish may acclimatize or adapt to our changing climate.

Effects of cold stress on juvenile Piaractus mesopotamicus and the mitigation by ß-carotene.

This study investigated the effects of cold stress on morphometrical and hematological biomarkers, energy metabolism, and oxidative stress in different tissues of P. mesopotamicus, and the protective role of ß-carotene. Fish were fed with a control diet (CD) and the same diet supplemented with 105 mg/kg ß-carotene (BD) for 60 days. After the feeding trial, fish fed CD or BD diets were exposed to control (24 °C) and low temperature (14 °C) for 24 h. Fish (CD and BD) exposed to thermal stress showed lower hepatosomatic index. The hemoglobin increased only in CD-fed fish exposed to 14 °C. Increased glycemia, plasmatic protein depletion, and decreased hepatic glycogen were observed in fish fed the CD, while only the lipid levels in liver were augmented in BD-fed fish exposed at 14 °C. Regarding the oxidative stress, increased antioxidant enzymes activity and lipid peroxidation were observed in CD-fed fish exposed to cold. The two-way ANOVA showed an interaction between dietary treatment and temperature for glucose and oxidative stress biomarkers, with the highest values recorded in 14 °C-exposed fish fed with the CD. Our study demonstrated that cold stress had the greatest impact on fish oxidative status, and ß-carotene reduces harmful effects induced by cold in P. mesopotamicus.

Sound the alarm: A meta-analysis on the effect of aquatic noise on fish behavior and physiology.

The aquatic environment is increasingly bombarded by a wide variety of noise pollutants whose range and intensity are increasing with each passing decade. Yet, little is known about how aquatic noise affects marine communities. To determine the implications that changes to the soundscape may have on fishes, a meta-analysis was conducted focusing on the ramifications of noise on fish behavior and physiology. Our meta-analysis identified 42 studies that produced 2,354 data points, which in turn indicated that anthropogenic noise negatively affects fish behavior and physiology. The most predominate responses occurred within foraging ability, predation risk, and reproductive success. Additionally, anthropogenic noise was shown to increase the hearing thresholds and cortisol levels of numerous species while tones, biological, and environmental noise were most likely to affect complex movements and swimming abilities. These findings suggest that the majority of fish species are sensitive to changes in the aquatic soundscape, and depending on the noise source, species responses may have extreme and negative fitness consequences. As such, this global synthesis should serve as a warning of the potentially dire consequences facing marine ecosystems if alterations to aquatic soundscapes continue on their current trajectory.

Comparative iTRAQ-Based Quantitative Proteomic Analysis of Pelteobagrus vachelli Liver under Acute Hypoxia: Implications in Metabolic Responses.

More and more frequently these days, aquatic ecosystems are being stressed by nutrient enrichment, pollutants, and global warming, leading to a serious depletion in oxygen concentrations. Although a sudden, significant lack of oxygen will result in mortality, fishes can have an acute behavior (e.g., an increase in breathing rate, reduction in swimming frequency) and physiology responses (e.g., increase in oxygen delivery, and reduction in oxygen consumption) to hypoxia, which allows them to maintain normal physical activity. Therefore, in order to shed further light on the molecular mechanisms of hypoxia adaptation in fishes, the authors conduct comparative quantitative proteomics on Pelteobagrus vachelli livers using iTRAQ. The research identifies 511 acute hypoxia-responsive proteins in P. vachelli. Furthermore, comparison of several of the diverse key pathways studied (e.g., peroxisome pathway, PPAR signaling pathway, lipid metabolism, glycolysis/gluco-neogenesis, and amino acid metabolism) help to articulate the different mechanisms involved in the hypoxia response of P. vachelli. Data from proteome analysis shows that P. vachelli can have an acute reaction to hypoxia, including detoxification of metabolic by-products and oxidative stress in light of continued metabolic activity (e.g., peroxisomes), an activation in the capacity of catabolism to get more energy (e.g., lipolysis and amino acid catabolism), a depression in the capacity of biosynthesis to reduce energy consumption (e.g., biosynthesis of amino acids and lipids), and a shift in the aerobic and anaerobic contributions to total metabolism. The observed hypoxia-related changes in the liver proteome of the fish can help to understand or can be related to the hypoxia-related response that takes place in similar conditions in the liver or other proteomes of mammals.

Characterization of Na+ transport to gain insight into the mechanism of acid-base and ion regulation in white sturgeon (Acipenser transmontanus).

Freshwater fish actively take up ions via specific transporters to counter diffusive losses to their hypotonic environment. While much is known about the specific mechanisms employed by teleosts, almost nothing is known about the basal fishes, such as white sturgeon (Acipenser transmontanus) which may offer insight into the evolution of osmo- and ionoregulation in fishes. We investigated Na+ uptake in juvenile white sturgeon in the presence and absence of transporter inhibitors. We found that sturgeon acclimated to 100µmoll-1 Na+ have Na+ uptake kinetics typical of teleosts and that a Na+/H+ exchanger (NHE) is the predominant transporter for Na+ uptake. White sturgeon are tolerant to hypercarbia-induced respiratory acidoses and recover blood pH (pHe) at 1.5kPa PCO2 but not at higher PCO2 (6kPa PCO2) where they preferentially regulate intracellular pH (pHi). It was hypothesized that during exposure to hypercarbia Na+ uptake would increase at CO2 tensions at which fish were capable of pHe regulation but decrease at higher tensions when they were preferentially regulating pHi. We found that Na+ uptake did not increase at 1.5kPa PCO2, but at 6kPa PCO2 Na+ uptake was reduced by 95% while low water pH equivalent to 6kPa PCO2 reduced Na+ uptake by 71%. Lastly, we measured net acid flux during hypercarbia, which indicates that net acid flux is not associated with Na+ uptake. These findings indicate Na+ uptake in sturgeon is not different from freshwater teleosts but is sensitive to hypercarbia and is not associated with pHe compensation during hypercarbia.

Stress response of Salmo salar (Linnaeus 1758) facing low abundance infestation of Caligus rogercresseyi (Boxshall & Bravo 2000), an object in the tank, and handling.

This study looks at how low infestation loads of adult Caligus rogercresseyi and other stressors affect the physiology of Salmo salar. Experimental fish groups were with (infested) or without (control) exposure to the parasite. The parasite cohort was followed for 78 days post-infestation (dpi), and only adult lice were observed. Additional stressors were applied at 60 and 75 dpi. The analysis included measurements of fish physiology and weight. Low-level infestations by adult C. rogercresseyi for more than 50 dpi induced moderate stress in S. salar as well as a high energy demand and increased small skin mucous cells. Threshold lice loads were identified, and above those loads, a high stress response was observed. Additional stressors altered fish physiology, inducing downregulation of the cortisol response after the first stressor and upregulation after the second stressor, but infested fish responded more strongly. Parasitism by C. rogercresseyi is energetically demanding, affecting the primary and secondary responses (e.g. cortisol and glucose levels), as well as the tertiary response (fish weight).

Development of a modified cortisol extraction procedure for intermediately sized fish not amenable to whole-body or plasma extraction methods.

The corticosteroid hormone cortisol is the central mediator of the teleost stress response. Therefore, the accurate quantification of cortisol in teleost fishes is a vital tool for addressing fundamental questions about an animal's physiological response to environmental stressors. Conventional steroid extraction methods using plasma or whole-body homogenates, however, are inefficient within an intermediate size range of fish that are too small for phlebotomy and too large for whole-body steroid extractions. To assess the potential effects of hatchery-induced stress on survival of fingerling hatchery-reared Spotted Seatrout (Cynoscion nebulosus), we developed a novel extraction procedure for measuring cortisol in intermediately sized fish (50-100 mm in length) that are not amenable to standard cortisol extraction methods. By excising a standardized portion of the caudal peduncle, this tissue extraction procedure allows for a small portion of a larger fish to be sampled for cortisol, while minimizing the potential interference from lipids that may be extracted using whole-body homogenization procedures. Assay precision was comparable to published plasma and whole-body extraction procedures, and cortisol quantification over a wide range of sample dilutions displayed parallelism versus assay standards. Intra-assay %CV was 8.54%, and average recovery of spiked samples was 102%. Also, tissue cortisol levels quantified using this method increase 30 min after handling stress and are significantly correlated with blood values. We conclude that this modified cortisol extraction procedure provides an excellent alternative to plasma and whole-body extraction procedures for intermediately sized fish, and will facilitate the efficient assessment of cortisol in a variety of situations ranging from basic laboratory research to industrial and field-based environmental health applications.

Salinity stress in the black-chinned tilapia Sarotherodon melanotheron.

Physiological and morphological acclimation capacities of black-chinned tilapia, Sarotherodon melanotheron were studied from fish to gill cell level when fish are maintained in freshwater, seawater, and hypersaline conditions. Fish osmoregulatory capacity, gill ionocyte morphology, osmo-respiratory compromise, O2 consumption rate, branchial antioxidative defense, and cell apoptosis were considered. Captive juvenile tilapias were maintained in controlled freshwater conditions (FW: 0.4 ppt; 12 mOsm kg-1) or gradually transferred to seawater (SW: 32 ppt; 958 mOsm kg-1) and concentrated SW (cSW: 65 ppt; 1920 mOsm kg-1). After 15 days in these conditions, blood osmolality and chloride ion concentration were determined. Gill ionocyte density and morphology were measured using immunolabelled histological sections to specifically detect the sodium pump (NKA). Gill osmo-respiratory compromise was also calculated along with oxygen consumption rates from normoxic to hypoxic conditions from excised gills (indirect respirometry). Finally, catalase and caspase 3/7activities were recorded from gill extracts. Results indicate that elevated salinity induces an osmotic imbalance and a profound morphological change with proliferating and hypertrophied ionocytes. This thickening of the gill interlamellar cell mass and the shortening of the lamellae induce a reduced osmo-respiratory ratio and reduced respiratory capacity under both normoxic and hypoxic conditions. Although salinity changes do not affect one of the major antioxidative defense mechanism, it strongly affects apoptosis that appears the most elevated in SW. However, in freshwater condition, fish can maintain their osmotic balance with a low ionocyte density, a low apoptotic level and a drastically reduced O2 consumption in normoxic condition that is maintained in hypoxia. Therefore, S. melanotheron presents the typical functional remodeling due to environmental salinity changes ranging from FW to SW. However, elevated seawater induces major cellular stress inducing a profound gill morphofunctional dysfunctioning. While cell apoptosis is reduced, ionocyte proliferation is massively increased with impaired osmotic regulation and reduced O2 consumption both in normoxic and hypoxic conditions.

Unraveling the molecular mechanisms of fish physiological response to freshwater salinization: A comparative multi-tissue transcriptomic study in a river polluted by potash mining.

Freshwater salinization is an escalating global environmental issue that threatens freshwater biodiversity, including fish populations. This study aims to uncover the molecular basis of salinity physiological responses in a non-native minnow species (Phoxinus septimaniae x P. dragarum) exposed to saline effluents from potash mines in the Llobregat River, Barcelona, Spain. Employing high-throughput mRNA sequencing and differential gene expression analyses, brain, gills, and liver tissues collected from fish at two stations (upstream and downstream of saline effluent discharge) were examined. Salinization markedly influenced global gene expression profiles, with the brain exhibiting the most differentially expressed genes, emphasizing its unique sensitivity to salinity fluctuations. Pathway analyses revealed the expected enrichment of ion transport and osmoregulation pathways across all tissues. Furthermore, tissue-specific pathways associated with stress, reproduction, growth, immune responses, methylation, and neurological development were identified in the context of salinization. Rigorous validation of RNA-seq data through quantitative PCR (qPCR) underscored the robustness and consistency of our findings across platforms. This investigation unveils intricate molecular mechanisms steering salinity physiological response in non-native minnows confronting diverse environmental stressors. This comprehensive analysis sheds light on the underlying genetic and physiological mechanisms governing fish physiological response in salinity-stressed environments, offering essential knowledge for the conservation and management of freshwater ecosystems facing salinization.

Evaluation of lead exposure effects on tissue accumulation, behavior, morphological and hemato-biochemical changes in common carp, Cyprinus carpio.

BACKGROUND: Heavy metal pollution, particularly lead (Pb), poses a significant threat to aquatic ecosystems and their inhabitants, threatening their delicate balance and long-term viability. This study highlights the urgent need to mitigate heavy metal pollution in aquatic ecosystems. OBJECTIVE: This study investigates Pb(NO3)2 exposure effects on tissue accumulation, behavioral abnormalities, and hemato-biochemical parameters in common carp (Cyprinus carpio), a widely distributed freshwater fish species. METHODOLOGY: Fish (115 ± 5.23 g) were exposed to various Pb(NO3)2 concentrations for 10 and 20 days, representing control (0 %), 25 %, 50 %, and 75 % of the LC50 equivalent to 19.33, 38.66, and 58.0 mg/l, respectively. The standard manual procedure was used for blood sampling. The lead concentration in fish tissue was determined using an atomic absorption spectrophotometer. RESULTS: Results revealed that fish gills showed significant (P < 0.05) increase in Pb(NO3)2 after 10 days, further rising after 20 days. Liver concentrations also rose significantly (P < 0.05) with prolonged exposure and increasing Pb levels. Muscle had lower concentrations. Hematological parameters (RBC, WBC, HB, HCT) decreased with higher Pb(NO3)2 levels. Behavioral and morphological changes were significantly more pronounced in the exposure groups when compared to the control group. Hepatic enzyme activities (AST, ALT), glucose, and lipid levels increased, while total protein decreased. CONCLUSIONS: The study highlights Pb(NO3)2 harmful effects on common carp, impacting tissue accumulation, hematological parameters, and biochemical disruptions. It emphasizes the need to monitor and mitigate heavy metal pollution in aquatic environments to safeguard freshwater organisms and ecosystems, and to further increase our understanding of Pb toxicity in freshwater ecosystems.

Illicit Drugs in Surface Waters: How to Get Fish off the Addictive Hook.

The United Nations World Drug Report published in 2022 alarmed that the global market of illicit drugs is steadily expanding in space and scale. Substances of abuse are usually perceived in the light of threats to human health and public security, while the environmental aspects of their use and subsequent emissions usually remain less explored. However, as with other human activities, drug production, trade, and consumption of drugs may leave their environmental mark. Therefore, this paper aims to review the occurrence of illicit drugs in surface waters and their bioaccumulation and toxicity in fish. Illicit drugs of different groups, i.e., psychostimulants (methamphetamines/amphetamines, cocaine, and its metabolite benzoylecgonine) and depressants (opioids: morphine, heroin, methadone, fentanyl), can reach the aquatic environment through wastewater discharge as they are often not entirely removed during wastewater treatment processes, resulting in their subsequent circulation in nanomolar concentrations, potentially affecting aquatic biota, including fish. Exposure to such xenobiotics can induce oxidative stress and dysfunction to mitochondrial and lysosomal function, distort locomotion activity by regulating the dopaminergic and glutamatergic systems, increase the predation risk, instigate neurological disorders, disbalance neurotransmission, and produce histopathological alterations in the brain and liver tissues, similar to those described in mammals. Hence, this drugs-related multidimensional harm to fish should be thoroughly investigated in line with environmental protection policies before it is too late. At the same time, selected fish species (e.g., Danio rerio, zebrafish) can be employed as models to study toxic and binge-like effects of psychoactive, illicit compounds.

Early life stage mechanisms of an active fish species to cope with ocean warming and hypoxia as interacting stressors.

Ocean's characteristics are rapidly changing, modifying environmental suitability for early life stages of fish. We assessed whether the chronic effects of warming (24 °C) and hypoxia (<2-2.5 mg L-1) will be amplified by the combination of these stressors on mortality, growth, behaviour, metabolism and oxidative stress of early stages of the white seabream Diplodus sargus. Combined warming and hypoxia synergistically increased larval mortality by >51%. Warming induced faster growth in length and slower gains in weight when compared to other treatments. Boldness and exploration were not directly affected, but swimming activity increased under all test treatments. Under the combination of warming and hypoxia, routine metabolic rate (RMR) significantly decreases when compared to other treatments and shows a negative thermal dependence. Superoxide dismutase and catalase activities increased under warming and were maintained similar to control levels under hypoxia or under combined stressors. Under hypoxia, the enzymatic activities were not enough to prevent oxidative damages as lipid peroxidation and DNA damage increased above control levels. Hypoxia reduced electron transport system activity (cellular respiration) and isocitrate dehydrogenase activity (aerobic metabolism) below control levels. However, lactate dehydrogenase activity (anaerobic metabolism) did not differ among treatments. A Redundancy Analysis showed that ∼99% of the variability in mortality, growth, behaviour and RMR among treatments can be explained by molecular responses. Mortality and growth are highly influenced by oxidative stress and energy metabolism, exhibiting a positive relationship with reactive oxygen species and a negative relationship with aerobic metabolism, regardless of treatment. Under hypoxic condition, RMR, boldness and swimming activity have a positive relationship with anaerobic metabolism regardless of temperature. Thus, seabreams may use anaerobic reliance to counterbalance the effects of the stressors on RMR, activity and growth. The outcomes suggests that early life stages of white seabream overcame the single and combined effects of hypoxia and warming.