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Abstract Background Mobility restriction is the most effective measure to control the spread of infectious disease at its early stage, especially if a cure and vaccine are not available. When control of the coronavirus disease 2019 (COVID-19) required strong precautionary measures, lockdowns were necessarily implemented in countries around the globe. Public health risk communication about the justification and scope of a lockdown was challenging as it involved a conflict between solidarity and individual liberty and a trade-off between various values across groups with different socioeconomic statuses. In the study, we examined public responses to the government-announced “circuit breaker” (a local term for lockdown) at four-time points in Singapore: (1) entry, (2) extension, (3) exit of lockdown ‘phase 1’ and (4) entry of lockdown ‘phase 2’. Methods We randomly collected 100 comments from the relevant articles on new organisations’ Facebook and Instagram pages and conducted preliminary coding. Later, additional random 20 comments were collected to check the data saturation. Content analysis was focused on identifying themes that emerged from the responses across the four-time points. Results At the entry, public support for the lockdown was prevalent; yet most responses were abstract with uncertainty. At six weeks of lockdown, initial public responses with uncertainty turned into salient narratives of their lived experiences and hardship with lockdown and unmasking of societal weaknesses caused by COVID-19. At the entry to phase 2, responses were centred on social-economic impact, disparity, and lockdown burnout with the contested notion of continuing solidarity. A temporal pattern was seen in the rationalisation of the lockdown experience from trust, anxiety, attribution of pandemic and lockdown, blaming of non-compliant behaviours, and confusion. Conclusions The findings indicated a temporal evolution of public responses from solidarity, attribution of the sustained pandemic, increasing ambiguity towards strong precautionary measures, concerns about economic hardship and mental well-being to worsened social vulnerability, where the government’s restrictive policies were questioned with anxiety and confusion. Public health risk communication in response to COVID-19 should be transparent and address health equity and social justice to enhance individual and collective responsibility in protecting the public from the pandemic.

Objective: The project was designed to compare the effectiveness of brief intervention (BI) versus simple advice (SA) in the secondary prevention of hazardous alcohol consumption.Methods: A randomized controlled trial with a 12-month follow-up was conducted. A total of 74 community-based primary care practices (328 physicians) located in 13 Spanish autonomous regions were recruited initially. Out of 546 men screened, only 229 were randomized into BI (n = 104) and SA (n = 125); 44.6% of practices finalized the study. The interventions on the BI group consisted of a 15-minute counselling visit carried out by physicians which included: (i) alcohol quantification, (ii) information on safe limits, (iii) advice, (iv) drinking limits agreement, (v) self-informative booklet with drinking diary record and (vi) unscheduled reinforcement visits. The SA group spent 5 minutes which included (i), (ii) and (iii).Results: There were no significant differences between both groups at baseline on alcohol use, age, socioeconomic status and CAGE score. After the 12-month follow-up there was a significant decrease in frequency of excessive drinkers (67% of BI group reached targeted consumption, versus 44% of SA; P < 0.001) as well as weekly alcohol intake reduction (BI reached 52 versus 32% in SA; P < 0.001). A trend to improve outcome with the number of reinforcement visits was found with BI. The only predictor of success was the initial alcohol consumption level.Conclusions: Brief intervention is more effective than simple advice to reduce alcohol intake on adult men who attend primary care services in Spain. [ABSTRACT FROM AUTHOR]

The black piranha ( Serrasalmus rhombeus ), a widely spread species in the rivers of the Amazon basin, plays a vital role as both key predator and important prey. Despite its essential contribution to ecosystem stability, there is a lack of information regarding its genetic diversity and population dynamics in the central Amazon region. As the Amazon continues to undergo environmental changes in the context of growing anthropogenic threats, such knowledge is fundamental for assist in the conservation of this species. This study is the first to analyze the genetic diversity and population structure of S. rhombeus in the central Amazon region using high-resolution genomic data. We employed a Genotyping-by-Sequencing approach with 248 samples across 14 study sites from various tributaries, encompassing diverse water types (black, white, and clear water) and characterized by 34 physiochemical parameters. The data reveals low diversity accompanied by pronounced signs of inbreeding in half of the sites and robust genetic differentiation and variation among sites and within-sites. Surprisingly, we also found evidence of higher dispersal capacity than previously recognized. Our analysis exposed a complex and high population structure with genetic groups exclusive to some sites. Gene flow was low and some groups presented ambiguous genealogical divergence index ( gdi ) signals, suggesting the occurrence of potential cryptic species. Moreover, our results suggest that the population structure of black piranha appears more influenced by historical events than contemporary factors. These results underscore the need to give greater attention to this keystone species, for which no regulatory framework or conservation strategies is presently in effect., Competing Interests: The authors declare no conflicts of interest., (© 2025 The Author(s). Ecology and Evolution published by John Wiley & Sons Ltd.)

Amazonian floodplain lakes, distinguished by their water types, are crucial ecosystems for fish biodiversity. In these ecosystems, the annual hydrological cycle, known as the "flood pulse," is the primary driving force for fish productivity, providing habitat and feeding opportunities. However, how seasonal water level changes affect fish assemblages and feeding guild responses in floodplains with varying watershed characteristics is still poorly understood. We conducted a comparative stable isotope study in both a white-water and a black-water floodplain lake to investigate fish trophic dynamics during periods of rising and low water levels. Analyses of a broad taxonomic range of fish (seven orders and 27 families, with 73 and 82 taxa in the studied lakes, respectively) revealed that the fish assemblages in the studied white-water and black-water lakes exhibited different trophic dynamics in response to changes induced by the hydrological cycle. In contrast to the white-water lake, a strong, trophic guild-related effect shaped the δ 13 C and δ 15 N dynamics in the black-water lake. As a result, the fish assemblage in the black-water lake experienced significant trophic shifts with generally opposite dynamics over the water levels compared to the white-water lake. In the black-water lake, water level changes caused alterations in trophic niche width in almost all analyzed guilds (carnivorous, detritivorous, herbivorous, invertivorous, omnivorous, planktivorous), while this was less consistent in the white-water lake. Our results suggest that the fish assemblage in the nutrient-poor black-water lake is more dependent on the annual flood pulse and associated resources than in the white-water lake. These findings may further imply a relatively higher vulnerability of the black-water lake to alterations in the regular flood pulse compared to the white-water lake, indicating greater stability in feeding conditions and fish trophic dynamics in the latter., (© 2025 Fisheries Society of the British Isles.)

The pirarucu is one of the very few obligate air-breathing fish, employing a gigantic, highly vascularized air-breathing organ (ABO). Traditionally, the ABO is thought to serve mainly for O 2 uptake (ṀO 2 ), with the gills providing the major route for excretion of CO 2 (ṀCO 2 ) and N-waste. However, under aquatic hypercapnia, a common occurrence in its natural environment, branchial ṀCO 2 to the water may become impaired. Under these conditions, does the ABO become an important route of ṀCO 2 excretion to the air? We have answered this question by measuring ṀCO 2 and ṀO 2 in both air and water phases, as well as the pattern of air-breathing, in pirarucu under aquatic normocapnia and hypercapnia (3% CO 2 ). Indeed, ṀCO 2 to the air phase via the ABO increased 2- to 3-fold during exposure to high water PCO 2 , accounting for 59-71% of the total, with no change in the dominant contribution of the ABO to ṀO 2 (71-75% of the total). These adjustments were quickly reversed upon restoration of aquatic normocapnia. During aquatic hypercapnia, ṀCO 2 via the ABO became more effective over time, and the pattern of air-breathing changed, exhibiting increased frequency and decreased breath volume. Ammonia-N excretion (86-88% of total) dominated over urea-N excretion and tended to increase during exposure to aquatic hypercapnia. We conclude that the ability of the ABO to take on the dominant role in CO 2 excretion when required may have been an important driver in the original evolution of air-breathing, as well as in the functionality of the ABO in modern air-breathing fish., Competing Interests: Declarations. Ethical approval: All procedures were in compliance with Brazilian national animal care regulations, and those of the Brazilian National Institute for Research of the Amazon (INPA) in Manaus, Brazil under protocol 027/2015. Competing interests: Bernd Pelster is an editor of this journal, but had no role in the reviewing or publication process., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The degree of tolerance to adverse conditions ultimately shapes a species' vulnerability to environmental changes. Some studies have reported limited thermal tolerance due to hypoxia in fish employing aquatic respiration. However, there is a lack of information regarding the effects of hypoxia on thermal tolerance in fish exhibiting bimodal respiration. A set of Amazonian fish species has adaptations to breathe air when oxygen in water is not enough to fulfil demand. Additionally, loricariid species within this group possess stomach adaptations for air breathing. The Loricariidae family exhibits varying stomach types and observed morphological differences could influence their ability to obtain oxygen from the air. This ability may, in turn, have consequences for the thermal tolerance of these species. Our objective was to assess the effects of hypoxia on thermal tolerance, along with the physiological (whole-animal metabolic rates and mitochondrial respiration) and behavioural mechanisms involved, in two facultative air-breathing species: Pterygoplichthys pardalis and Ancistrus dolichopterus. These species showcase morphological distinctions in their stomachs, with the former having a higher capacity to obtain oxygen from the air. Thermal tolerance in P. pardalis remained unaffected by dissolved oxygen in the water when air access was available but decreased when access to the water surface was restricted, specifically in hypoxic conditions. Conversely, the thermal tolerance of A. dolichopterus decreased below the critical oxygen partial pressure (Pcrit), even with access to air, highlighting their limited ability to obtain oxygen through their adapted stomach. Our results underscore that air breathing enhances thermal tolerance, but this effect is prominent only in species with a higher capacity for air breathing., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2025. Published by The Company of Biologists.)

Optical characterization of dissolved organic carbon (DOC) freshly collected from the circumneutral "white water" of the Rio Solimoes revealed that it had lower aromaticity, lower molecular weight, and a greater autochthonous content than DOC from the acidic "black water" of the Rio Negro. The tambaqui (Colossoma macropomum), a characid member of the Serrasalmidae, is a model neotropical fish that migrates annually between the two rivers. We analysed ionoregulatory responses of the tambaqui over 24 h in ion-poor water at pH 7.0 and pH 4.0 in the absence and presence of 10 mg L -1 Rio Solimoes DOC ("SOL DOC"). Measured parameters included transepithelial potential (TEP) across the gills, net flux rates, and plasma concentrations of Na + , Cl - , ammonia, and urea, and branchial Na + , K + -ATPase, H + , ATPase, and carbonic anhydrase activities. Results were compared to our earlier study using similar protocols to examine the ionoregulatory effects of 10 mg L -1 DOC ("SGC DOC") collected from black water at São Gabriel da Cachoeira (SGC) in the upper Rio Negro. At pH 7.0, SOL DOC had no effect on the negative TEP across the gills. Exposure to pH 4.0 caused a marked depolarization of the TEP to positive values that was not ameliorated by the presence of SOL DOC. This contrasts with SGC DOC that drove TEP more negative at pH 7.0 and fully protected against the depolarization at pH 4.0. However, SOL DOC promoted positive balance of Na + and Cl - at pH 7.0 and helped ameliorate the negative balance of these ions seen at pH 4.0. This again contrasts with SGC DOC that exacerbated ion losses at pH 4.0. The protective effects of SOL DOC on ion balance maybe related to increased v-type H + ATPase activity in the gills, and unrelated to TEP. The very different responses to the two DOCs are discussed with respect to their optical properties, the time that they were in storage prior to testing (SOL <1 month, SGC 2 years), and the life history of the tambaqui in the two rivers., (© 2025 Fisheries Society of the British Isles.)

The annual flood pulse is a defining feature of Amazonian floodplain lakes, creating a highly variable environment that influences resource availability, such as food and habitat. These cyclical changes necessitate a high degree of adaptability among fish species, many of which have evolved specialized strategies to cope with the fluctuating conditions. In 2023, the Amazon basin experienced a record-breaking drought event, leading to mass mortality of Amazonian fish and other wildlife. This study examines the effect of this extreme event on fish condition in white-water (Rio Solimões basin) and black-water (Rio Negro basin) floodplain lakes. These contrasting environments provide a unique opportunity to study how different water qualities and extreme water-level fluctuations impact fish condition. Research was conducted during the normal low-water period in November 2019 and the drastically decreased water levels in November 2023. The main objective was to understand how extreme water-level fluctuations affect fish health and nutritional status. A total of 585 fishes were analyzed, with 294 from white-water and 291 from black-water, representing different feeding types to provide a comprehensive picture of changes in fish condition. Water-level changes had a statistically significant impact on fish condition in both areas. Comparing low-water and extreme low-water levels, fish condition was consistently higher during the normal low-water period. The linear mixed-effects model revealed that the intensity of the low-water season had a significant effect on fish length-adjusted mass, suggesting that the decrease in water level is associated with an overall decrease in fish length-adjusted mass. When comparing the mean water-level effect (Glass's Δ) between low-water and extreme low-water levels, we found a bigger effect in the black-water system than in the white-water system. This difference may be attributed to the lower nutrient content and higher levels of humic acids and refractory dissolved organic matter in black-water, which can further limit primary productivity and food availability for fishes., (© 2025 Fisheries Society of the British Isles.)

Since Amazonian fish live close to their maximum thermal limits, this makes them vulnerable to the effects of global warming. The aim of this study was to evaluate the oxidative stress and antioxidant enzymatic and biochemical responses of the plasma, liver and muscle of tambaqui (Colossoma macropomum) exposed to a rising gradient of water temperature. One hundred and twenty (N = 120) juvenile tambaqui were exposed to four temperature levels, these being: the environmental temperature of the season (T env - 25.7-30 °C), 31 °C, 34 °C and 37 °C, following a completely randomized design with three replicates for a period of 60 days. Liver and muscle samples were used to determine the levels of the enzymes superoxide dismutase (SOD), catalase (CAT) glutathione peroxidase (GPx) and lipid peroxidation (LPO). Plasma levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were measured. A histopathological damage assessment (HAI) was performed using liver samples and the results showed an increase in lipid peroxidation in the muscle and liver of animals kept at 37 °C in relation to other temperatures. Enzyme responses were tissue-specific in the liver and muscle. In the liver, the reduction of CAT, SOD and GPx levels of the animals was observed at 37 °C compared to those maintained at T env and SOD and GPx in relation to animals maintained at 31 and 34 °C. The GPx enzyme showed higher activity at 34 and 37 °C compared to the other evaluated temperatures. At 37 °C, plasma levels of ALT and AST were higher than the other temperatures evaluated, as well as an increase in histopathological damage. In this way, in a scenario of warming of the waters of the Amazon or even of the systems used for rearing of the species, the tambaqui will be able to cope with temperatures of up to 34 °C, without affecting its antioxidant capacity. However, at 37 °C, oxidative stress levels and increased liver damage suggest a reduction in antioxidant capacity due to tissue impairment of the organ and general loss of animal performance as it approaches the upper thermal limit of the species., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The Arctic is warming three times faster than the global average, imposing challenges to cold-adapted fish, such as Arctic char (Salvelinus alpinus). We evaluated stress and metabolic responses of Arctic char to different thermal acclimation scenarios to determine whether responses to thermal variation differed from those to stable exposures. Fish were exposed for 7 days to one of four treatments: (1) control (12°C); (2) mean (16°C), corresponding to the mean temperature of the diel thermal cycle; (3) constant high temperature (20°C); and (4) diel thermal cycling (12 to 20°C every 24 h). Exposure to 20°C causes increases plasma lactate and glucose, an imbalance in antioxidant systems, and oxidative stress in the liver. The 20°C treatment also elevated fractional rates of protein synthesis and caused oxidative stress in the heart. Stress responses were more pronounced in diel thermal cycling than in mean (16°C) fish, indicating that peak exposure temperatures or variation are physiologically important. Cortisol was highest in diel thermal cycling fish and oxidative stress was noted in the liver. Gill Na+/K+-ATPase activity was also significantly reduced in diel thermal cycling fish, suggesting gill remodeling in response to an osmoregulatory stress. Exposure to a constant 20°C was more challenging than a diel thermal cycle, demonstrating the importance of daily cooling to recovery. Arctic char inhabit a thermally variable environment and understanding how this impacts their physiology will be critical for informing conservation strategies in the context of a rapidly warming Arctic., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Elements that interfere with reproductive processes can have profound impacts on population and the equilibrium of ecosystems. Global warming represents the major environmental challenge of the 21st century, as it will affect all forms of life in the coming decades. Another coexisting concern is the persistent pollution by pesticides, particularly the herbicide Atrazine (ATZ), which is responsible for a significant number of contamination incidents in surface waters worldwide. While it is hypothesized that climate changes will significantly enhance the toxic effects of pesticides, the actual impact of these phenomena remain largely unexplored. Here, we conducted a climate-controlled room experiment to assess the interactive effects of the projected 2100 climate scenario and environmentally realistic ATZ exposures on the reproductive function of male zebrafish. The gonadosomatic index significantly decreased in fish kept in the extreme scenario. Cellular alterations across spermatogenesis phases led to synergic decreased sperm production and increased germ cell sloughing and death. ATZ exposure alone or combined with climate change effects, disrupted the transcription levels of key genes involved in steroidogenesis, hormone signaling and spermatogenesis regulation. An additive modulation with decreased 11-KT production and increased E2 levels was also evidenced, intensifying the effects of androgen/estrogen imbalance. Moreover, climate change and ATZ independently induced oxidative stress, upregulation of proapoptotic gene and DNA damage in post-meiotic germ cell, but the negative effects of ATZ were greater at extreme scenario. Ultimately, exposure to simulated climate changes severely impaired fertilization capacity, due to a drastic reduction in sperm motility and/or viability. These findings indicate that the future climate conditions have the potential to considerably enhance the toxicity of ATZ at low concentrations, leading to significant deleterious consequences for fish reproductive function and fertility. These may provide relevant information to supporting healthcare and environmental managers in decision-making related to climate changes and herbicide regulation., Competing Interests: Declaration of competing interest The authors declare that they have no competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The first studies on ion regulation in fish exposed to low pH, which were inspired by the Acid Rain environmental crisis, seemed to indicate that ion transport at the gills was completely and irreversibly inhibited at pH 4.0-4.5 and below. However, work on characid fish native to the Rio Negro, a naturally acidic, blackwater tributary of the Amazon River, found that they possess ion transport mechanisms that are completely insensitive to pHs as low as 3.25. As more species were examined it appeared that pH-insensitive transport was a trait shared by many, if not most, species in the Order Characiformes. Subsequently, a few other species of fish have been shown to be able to transport ions at low pH, in particular zebrafish (Danio rerio), which show rapid recovery of Na + uptake at pH 4.0 after initial inhibition. Measurements of rates of Na + transport during exposure to pharmacological agents that inhibit various transport proteins suggested that characiform fish do not utilize the generally accepted mechanisms for Na + transport that rely on some form of H + extrusion. Examination of zebrafish transport at low pH suggest the rapid recovery may be due to a novel Na + /K + exchanger, but after longer term exposure they may rely on a coupling of Na + /H + exchangers and NH 3 excretion. Further work is needed to clarify these mechanisms of transport and to find other acid-tolerant species to fully gain an appreciation of the diversity of physiological mechansisms involved., (© 2024. The Author(s).)

According to the IPCC, by the year 2100, rises in global temperature could reach up to 5 °C above current averages. On a planet-wide scale, this is one of the effects of climate changes that could have repercussions on the biological cycle of Aedes aegypti, the main arbovirus vector in urban environments and a transmitter of the arboviruses that cause dengue, Zika, chikungunya and urban yellow fever. The objective of this study was to evaluate morphological changes in Ae. aegypti eggs and embryos maintained in a climate change simulator. For this, specimens obtained from an insectarium were kept in four chambers that simulated the range of environmental scenarios predicted by the IPCC for the year 2100. The eggs obtained from each room were collected and transported to the laboratory for morphometric and morphological analysis, using confocal and scanning microscopy. Aedes aegypti eggs (n=20) were used to obtain the following variables: total width, total length, length-width ratio and diameter of the micropylar disc. Additionally, 20 embryos were used to obtain the data on head capsule length, width and length-width ratio. The data were subjected to a normality test and the means of each variable were compared using ANOVA and Tukey's post-hoc test, considering (p ≤ 0.05). A significant reduction (p < 0.05) was observed mainly in the mean lengths under the current-extreme scenario (587.5 and 553.6 μm, respectively), as well as in the widths under the current-mild scenario (171 and 158.4 μm, respectively). The length of the cephalic capsule was also affected, showing significant differences in the means under the current-intermediate scenario (189.5 and 208.5 μm, respectively), as well as in the widths between the current-intermediate scenarios (173.7 and 194.9 μm, respectively). The results suggest significant changes in the morphometry of Ae. aegypti eggs and embryos as a result of the climatic influences to which the adults were subjected, which may have an impact on vector population density and, consequently, on arbovirus dynamics in urban environments., Competing Interests: Declaration of competing interest All authors declare that they have no conflict of interest in this study., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Background: Amazonas was one of the most impacted Brazilian states by the COVID-19 pandemic. Mortality rates were high, and the health systems collapsed. It is important to identify possible intermediate reservoirs to avoid animal-to-human contamination. Several tropical fish are of commercial interest and are sold in large open-air markets in the region, representing a large economic and dietary importance., Objectives: This study aimed to verify if fish species of commercial importance, aerosols, and fish wastewater in local open-air markets, at a major capital city in the western Brazilian Amazon, are contaminated by SARS-CoV-2., Methods: 488 fish, 50 aerosol, and 45 wastewater samples were analyzed for the presence of SARS-CoV-2. The samples were subjected to extraction using the BIOGENE Viral DNA/RNA Extraction kit, and the molecular diagnosis was tested for SARS-CoV-2 using the Bio-Manguinhos SARS-CoV-2 (EDx) Molecular Kit., Results: It was not possible to detect the virus (Ct≤40, for Gene E) in these samples, however, in 181 samples of fish it was possible to detect the human RP gene (Ct≤35, for the RP Gene), indicating human contact. There was a high number of COVID-19 diagnoses in all city districts in which the samples were collected, showing that SARS-CoV-2 was circulating., Conclusion: This study indicates that fish of local commercial importance do not carry SARS-CoV-2 viral particles, despite circulation of SARS-CoV-2, and are not an important source of animal-to-human contamination. Despite these results, the human RP gene was found detectable in fish, air, and fish wastewater, showing that such places may carry human pathogens., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 de Sá Leitão et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Climatic events are affecting the Amazon basin and according to projections it is predicted the intensification of climate changes through increases in temperature and carbon dioxide (CO 2 ). Recent evidence has revealed that exposure to an extreme climate scenario elicits oxidative damage in some fish species, impairing their metabolism and physiology, contributing to their susceptibility. Thus, the comprehension of physiological alterations in Arapaima gigas (pirarucu) to the climatic changes forecasted for the next 100 years is important to evaluate its capability to deal with oxidative stress. The objective of this work was to determine whether antioxidant defense system is able to prevent muscle oxidative damage of pirarucu exposed 96 h to extreme climate scenario, as well as the effects of this exposition on muscle fatty acid levels. Lipid peroxidation and reactive oxygen species significantly increase in the muscle of pirarucus exposed to an extreme climate scenario compared to control, while muscle superoxide dismutase, catalase, and glutathione peroxidase were significantly lower. Total amount of saturated fatty acids (SFAs) was significantly higher in pirarucu exposed to an extreme climate scenario compared to control, while total content of monounsaturated (MUFAs) and polyunsaturated fatty acids (PUFAs) was significantly lower. Exposure to an extreme climate scenario causes muscular oxidative stress and that the antioxidant systems are inefficient to avoid oxidative damage. In addition, the increase of total SFAs and the decrease of MUFAs and PUFAs probably intend to maintain membrane fluidity while facing high temperature and CO 2 levels., Competing Interests: Declaration of competing interest No potential conflict of interest was reported by the authors., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Several studies highlighted the complexity of mixing pesticides present in Amazonian aquatic environments today. There is evidence that indicates that ongoing climate change can alter the pattern of pesticide use, increasing the concentration and frequency of pesticide applications. It is known that the combination of thermal and chemical stress can induce interactive effects in aquatic biota, which accentuates cell and molecular damage. However, considering that the effects of climate change go beyond the increase in temperature the objective of this study was to evaluate the effect of climate change scenarios proposed by 6 th IPCC report and a mixture of pesticides on the tambaqui (Colossoma macropomum). The hypothesis of this study is that the negative effects will be accentuated by the combination of an extreme climate changes scenario and a mixture of pesticides. To test the hypothesis, juvenile tambaqui were exposed to a combination of four pesticides (chlorpyrifos, malathion, carbendazim and atrazine) in two scenarios, one that simulates current environmental conditions and another that predicted the environmental scenario for the year 2100. Fish were subjected to the experimental conditions for 96 h. At the end of the experiment, samples of blood, gills, liver, brain, and muscle were obtained for hematological, genotoxic, biochemical, and histopathological analyses. The results demonstrate that environmentally realistic concentrations of pesticides, when mixed, can alter the biochemical responses of tambaqui. The extreme scenario promotes hematological adjustments, but impairs branchial antioxidant enzymes. There is an interaction between the mixture of pesticides and the extreme scenario, accentuating liver tissue damage, which demonstrates that even increased activity of antioxidant and biotransformation enzymes were not sufficient to prevent liver damage., Competing Interests: Declaration of competing interest The authors have no conflicts of interest to declare., (Copyright © 2024. Published by Elsevier B.V.)

Increases in temperature can affect the reproduction of fish by decreasing the quality of gametes for fertilization. Therefore, this study aimed to evaluate the in vivo effect of temperature on the production and sperm quality of Colossoma macropomum, which is an economically relevant species for Brazil, and other countries. Broodstock were exposed for 10 days at temperatures of 29 °C (n = 4) and 35 °C (n = 4). After exposure, semen was collected and sperm quality was evaluated for kinetic, biochemical, morphological parameters, membrane integrity, and oxygen consumption. The sperm quality of males of specimens of C. macropomum exposed in vivo to the higher temperature was compromised and showed a difference in all the analyses (P < 0.05). Sperm showed decreased motility (51.9 ± 11.6 s) compared to the control (61.3 ± 5.5 s); curvilinear (CLV), straight line (SLV), and average path (APV) velocities decreased, and straightness (STR) and beat cross frequency (BCF) increased; oxygen consumption decreased (32.8 ± 3.4 pmol. (s.ml) -1 , picomol per second per ml) compared to the control (46.6 ± 3.5 pmol. (s.ml) -1 ); and the activity of catalase (CAT) and glutathione S-transferase (GST) enzymes increased and decreased, respectively, in sperm from fish exposed to high temperatures. Furthermore, an increase in non-viable sperm with damaged membranes and sperm with altered morphology was observed. The observed alterations indicate that C. macropomum confined in environments with high temperatures possibly produces more sperm that are unviable for the fertilization process., Competing Interests: Declaration of Competing Interest The authors declare that there is no conflict of interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The Rio Negro basin of Amazonia (Brazil) is a hotspot of fish biodiversity that is under threat from copper (Cu) pollution. The very ion-poor blackwaters have a high dissolved organic carbon (DOC) concentration. We investigated the Cu sensitivity of nine Amazonian fish species in their natural blackwaters (Rio Negro). The acute lethal concentration of Cu (96 h LC 50 ) was determined at different dilutions of Rio Negro water (RNW) in ion-poor well water (IPW), ranging from 0 to 100%. The IPW was similar to RNW in pH and ionic composition but deficient in DOC, allowing this parameter to vary 20-fold from 0.4 to 8.3 mg/L in tests. The Biotic Ligand Model (BLM; Windward version 3.41.2.45) was used to model Cu speciation and toxicity over the range of tested water compositions, and to estimate lethal Cu accumulations on the gills (LA 50 ). The modeling predicted a high relative abundance of Cu complexes with DOC in test waters. As these complexes became more abundant with increasing RNW content, a concomitant decrease in free Cu 2+ was observed. In agreement with this modeling, acute Cu toxicity decreased (i.e. 96 h LC 50 values increase) with increasing RNW content. The three most sensitive species (Hemigrammus rhodostomus, Carnegiella strigatta and Hyphessobrycon socolofi) were Characiformes, whereas Corydoras schwartzi (Siluriformes) and Apistogramma agassizii (Cichliformes) were the most tolerant. These sensitivity differences were reflected in the BLM-predicted lethal gill copper accumulation (LA 50 ), which were generally lower in Characiformes than in Cichliformes. Using these newly estimated LA 50 values in the BLM allowed for accurate prediction of acute Cu toxicity in the nine Amazonian fish. Our data emphasize that the BLM approach is a promising tool for assessing Cu risk to Amazonian fish species in blackwater conditions characterized by very low concentrations of major ions but high concentrations of DOC., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Adalberto Luis Val reports financial support was provided by Foundation for Research Support of Amazonas State. Christopher Michael Wood reports financial support was provided by Canada Research Chairs program, and a visiting fellowship from the Science Without Borders Program (CNPq-Brazil). Work in Canada was supported by NSERC (Canada) Discovery grants (RGPIN-2017-03843 to CMW and RGPIN-2019-04400 to AC). Adalberto Luis Val reports financial support was provided by Brazilian National Council for the State Funding Agencies. Adalberto Luis Val reports financial support was provided by Coordination of Higher Education Personnel Improvement., (Copyright © 2023. Published by Elsevier Ltd.)

The green crab (Carcinus maenas) is an inshore species affected by intertidal zonation patterns, facing periods of emersion during low tide and submersion during high tide. During these periods of air and subsequent water exposure, these species can face physiological challenges. We examined changes in O2 consumption rate (ṀO2), and ammonia and urea excretion rates over sequential 14 h periods in seawater (32 ppt, control), in air and during recovery in seawater after air exposure (13°C throughout). At the end of each exposure, the anterior (5th) and posterior (8th) gills and the hepatopancreas were removed for measurements of oxidative stress parameters (TBARs and catalase in the gills and hepatopancreas, and protein carbonyls in the gills). ṀO2 remained unchanged during air exposure, but increased greatly (3.4-fold above control levels) during the recovery period. Ammonia and urea net fluxes were reduced by 98% during air exposure, but rebounded during recovery to >2-fold the control rates. Exchangeable water pools, rate constants of diffusive water exchange, unidirectional diffusive water flux rates (using tritiated water) and transepithelial potential were also measured during control and recovery treatments, but exhibited no significant changes. Damage to proteins was not observed in either gill. However, lipid damage occurred in the anterior (respiratory) gill after the air exposure but not in the posterior (ionoregulatory) gill or hepatopancreas. Catalase activity also decreased significantly in recovery relative to levels during air exposure in both the anterior gill and hepatopancreas, but not in the posterior gill. The crabs did not modify water metabolism or permeability. We conclude that ṀO2 was maintained but not enhanced during air exposure, while ammonia and urea-N excretion were impaired. As a result, all of these parameters increase greatly during re-immersion recovery, and oxidative stress also occurs. Clearly, emersion is not without physiological costs., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

The Amazon River basin sustains dramatic hydrochemical gradients defined by three water types: white, clear, and black waters. In black water, important loads of allochthonous humic dissolved organic matter (DOM) result from the bacterioplankton degradation of plant lignin. However, the bacterial taxa involved in this process remain unknown, since Amazonian bacterioplankton has been poorly studied. Its characterization could lead to a better understanding of the carbon cycle in one of the Earth's most productive hydrological systems. Our study characterized the taxonomic structure and functions of Amazonian bacterioplankton to better understand the interplay between this community and humic DOM. We conducted a field sampling campaign comprising 15 sites distributed across the three main Amazonian water types (representing a gradient of humic DOM), and a 16S rRNA metabarcoding analysis based on bacterioplankton DNA and RNA extracts. Bacterioplankton functions were inferred using 16S rRNA data in combination with a tailored functional database from 90 Amazonian basin shotgun metagenomes from the literature. We discovered that the relative abundances of fluorescent DOM fractions (humic-, fulvic-, and protein-like) were major drivers of bacterioplankton structure. We identified 36 genera for which the relative abundance was significantly correlated with humic DOM. The strongest correlations were found in the Polynucleobacter, Methylobacterium, and Acinetobacter genera, three low abundant but omnipresent taxa that possessed several genes involved in the main steps of the β-aryl ether enzymatic degradation pathway of diaryl humic DOM residues. Overall, this study identified key taxa with DOM degradation genomic potential, the involvement of which in allochthonous Amazonian carbon transformation and sequestration merits further investigation. IMPORTANCE The Amazon basin discharge carries an important load of terrestrially derived dissolved organic matter (DOM) to the ocean. The bacterioplankton from this basin potentially plays important roles in transforming this allochthonous carbon, which has consequences on marine primary productivity and global carbon sequestration. However, the structure and function of Amazonian bacterioplanktonic communities remain poorly studied, and their interactions with DOM are unresolved. In this study, we (i) sampled bacterioplankton in all the main Amazon tributaries, (ii) combined information from the taxonomic structure and functional repertory of Amazonian bacterioplankton communities to understand their dynamics, (iii) identified the main physicochemical parameters shaping bacterioplanktonic communities among a set of >30 measured environmental parameters, and (iv) characterized how bacterioplankton structure varies according to the relative abundance of humic compounds, a by-product from the bacterial degradation process of allochthonous DOM., Competing Interests: The authors declare no conflict of interest.

Ammonia is toxic to fish, and when associated with global warming, it can cause losses in aquaculture. In this study, we investigated the physiological and zootechnical responses of Arapaima gigas to the current scenarios and to RCP8.5, a scenario predicted by the IPCC for the year 2100 which is associated with high concentrations of environmental ammonia (HEA). Forty-eight chipped juvenile A. gigas were distributed in two experimental rooms (current scenario and RCP8.5) in aquariums with and without the addition of ammonia (0.0 mM and 2.44 mM) for a period of 30 days. The HEA, the RCP8.5 scenario, and the association of these factors affects the zootechnical performance, the ionic regulation pattern, and the levels of ammonia, glucose, triglycerides, sodium, and potassium in pirarucu plasma. The branchial activity of H + -ATPase was reduced and AChE activity increased, indicating that the species uses available biological resources to prevent ammonia intoxication. Thus, measures such as monitoring water quality in regard to production, densities, and the feed supplied need to be more rigorous and frequent in daily management in order to avoid the accumulation of ammonia in water, which, in itself, proved harmful and more stressful to the animals subjected to a climate change scenario.

The evaluation of contamination by domestic sewage is relevant in the Amazon region; however, it has neither been well-developed nor accompanied by research or monitoring programs. In this study, caffeine and coprostanol as indicators of sewage were investigated in water samples from Amazonian water bodies that crisscross the city of Manaus (Amazonas state, Brazil) and cover regions with distinct main land uses such as high-density residential, low-density residential, commercial, industrial, and environmental protection areas. Thirty-one water samples were studied based on their dissolved and particulate organic matter (DOM and POM) fractions. Quantitative determination of both caffeine and coprostanol was carried out using LC-MS/MS with APCI in the positive ionization mode. The streams of the urban area of Manaus had the highest concentrations of caffeine (1.47-69.65 μg L -1 ) and coprostanol (2.88-46.92 μg L -1 ). Samples from the peri-urban Tarumã-Açu stream and from the streams in the Adolpho Ducke Forest Reserve showed much lower concentrations of caffeine (20.20-165.78 ng L -1 ) and coprostanol (31.49-120.44 ng L -1 ). Samples from the Negro River showed a wider range of concentrations of caffeine (20.59-873.59 ng L -1 ) and coprostanol (31.72-706.46 ng L -1 ), with the highest values found in the outfalls of the urban streams. Levels of caffeine and coprostanol were significantly positively correlated in the different organic matter fractions. The coprostanol/(coprostanol + cholestanol) ratio proved to be a more suitable parameter than the coprostanol/cholesterol one in low-density residential areas. Proximity to densely populated areas and the flow of water bodies appear to influence the caffeine and coprostanol concentrations, which was observed in their clustering in the multivariate analysis. The results indicate that caffeine and coprostanol can be detected even in water bodies that receive very low domestic sewage input. Therefore, this study revealed that both caffeine in DOM and coprostanol in POM represent viable alternatives for use in studies and monitoring programs even in remote areas of the Amazon, where microbiological analyses are often unfeasible., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

Earth's biodiversity and human societies face pollution, overconsumption of natural resources, urbanization, demographic shifts, social and economic inequalities, and habitat loss, many of which are exacerbated by climate change. Here, we review links among climate, biodiversity, and society and develop a roadmap toward sustainability. These include limiting warming to 1.5°C and effectively conserving and restoring functional ecosystems on 30 to 50% of land, freshwater, and ocean "scapes." We envision a mosaic of interconnected protected and shared spaces, including intensively used spaces, to strengthen self-sustaining biodiversity, the capacity of people and nature to adapt to and mitigate climate change, and nature's contributions to people. Fostering interlinked human, ecosystem, and planetary health for a livable future urgently requires bold implementation of transformative policy interventions through interconnected institutions, governance, and social systems from local to global levels.

Climate change leads to an increase in water acidification and temperature, two environmental factors that can change fish appetite and metabolism, affecting fish population in both wild and aquaculture facilities. Therefore, our study tested if climate change affects gene expression levels of two appetite-regulating peptides - Neuropeptide Y (NPY) and Cholecystokinin (CCK) - in the brain of tambaqui, Colossoma macropomum. Additionally, we show the distribution of these genes throughout the body. Amino acid sequences of CCK and NPY of tambaqui showed high similarity with other Characiformes, with the closely related order Cypriniformes, and even with the more distantly related order Salmoniformes. High apparent levels of both peptides were expressed in all brain areas, while expression levels varied for peripheral tissues. NPY and CCK mRNA were detected in all peripheral tissues but cephalic kidney for CCK. As for the effects of climate change, we found that fish exposed to extreme climate scenario (800 ppm CO 2 and 4.5 °C above current climate scenario) had higher expression levels of NPY and lower expression levels of CCK in the telencephalon. The extreme climate scenario also increased food intake, weight gain, and body length. These results suggest that the telencephalon is probably responsible for sensing the metabolic status of the organism and controlling feeding behavior through NPY, likely an orexigenic hormone, and CCK, which may act as an anorexigenic hormone. To our knowledge, this is the first study showing the effects of climate change on the endocrine regulation of appetite in an endemic and economically important fish from the Amazon. Our results can help us predict the impact of climate change on both wild and farmed fish populations, thus contributing to the elaboration of future policies regarding their conservation and sustainable use., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The vitellogenin is composed by polypeptides that are precursors of egg yolk proteins that provides embryo and larvae nutrition. The mRNA encoding for vitellogenin Ab (Vtg-Ab; 4,536 bp long and 1,512 amino acids) were obtained by RNA-Seq library sequencing of pirarucu gonads. The Vtg-Ab sequences had high homology with Vtgs of other three teleosts species of the order Osteoglossiformes. The transcript of ovarian Vtg was identified based on structural criteria, and so we classify the Vtg of pirarucu as Vtg-Ab due to the truncated or shortened phosvitin (N-terminal end) and phosvitinless domain (C-terminal end). The Vtg-Ab of pirarucu present two major deletions with 133 amino acids in the Lipovitellin I domain and 89 amino acids in the truncated or shortened Phosvitin domain, both located in the N-terminal end region. The three-dimensional (3-D) structure Vtg-Ab protein shows the presence of a typical 4α-helices bundle protein that runs in anti-parallel. In general, the characterization of Vtg-Ab may be the useful elucidation of the hormonal regulation of vitellogenesis and improve the production of pirarucu for broodstock management in aquaculture and preparation of Vtg antibody production (species-specific) for sex identification., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

High CO 2 (hypercapnia) can impose significant physiological challenges associated with acid-base regulation in fishes, impairing whole animal performance and survival. Unlike other environmental conditions such as temperature and O 2 , the acute CO 2 tolerance thresholds of fishes are not understood. While some fish species are highly tolerant, the extent of acute CO 2 tolerance and the associated physiological and ecological traits remain largely unknown. To investigate this, we used a recently developed ramping assay, termed the Carbon Dioxide maximum (CD max ), that increases CO 2 exposure until loss of equilibrium (LOE) is observed. We investigated if there was a relationship between CO 2 tolerance and the Root effect, β-adrenergic sodium proton exchanger (βNHE), air-breathing, and fish habitat in 17 species. We hypothesized that CO 2 tolerance would be higher in fishes that lack both a Root effect and βNHE, breathe air, and reside in tropical habitats. Our results showed that CD max ranged from 2.7 to 26.7 kPa, while LOE was never reached in four species at the maximum PCO 2 we could measure (26.7 kPa); CO 2 tolerance was only associated with air-breathing, but not the presence of a Root effect or a red blood cell (RBC) βNHE, or fish habitat. This study demonstrates that the diverse group of fishes investigated here are incredibly tolerant of CO 2 and that although this tolerance is associated with air-breathing, further investigations are required to understand the basis for CO 2 tolerance., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The production of tambaqui Colossoma macropomum has recently reached a milestone, being considered the main native species produced in South American continental waters. Despite the importance of this fish, its immunity is poorly understood, and global warming could pose severe risks to its health as increasing water temperature leads to an increase in the incidence of parasitic diseases. In an experimental context based on the high-emission scenario of the 5th Intergovernmental Panel on Climate Change (IPCC) report, we evaluated the synergistic effect of exposure to the extreme climate change scenario (RCP8.5) during two exposure periods (7 and 30 days) and two levels of parasitism by monogeneans (low and high). The goal was to understand how the tambaqui immune system will react to this challenge. To achieve this goal, we analyzed the expression of nine immunity-related genes (jak3, stat3, il-10, socs1, casp1, il-1β, tp53, bcl2, and hif-1α) in the spleen. Our main findings showed downregulation in the jak3/stat3 pathway, genes related to the control of inflammation and apoptosis, in addition to upregulation of proinflammatory genes and those related to pyroptosis during the first 7 days of exposure to the extreme climate scenario, also indicating a stage of immunodepression in these animals. After 30 days of exposure, all genes tended to return to similar levels in the current scenario, possibly due to the decrease in parasite load caused by chronic exposure to the extreme scenario. Our data strongly suggest that the increase in parasitism intensity caused by the extreme climate change scenario is responsible for disturbances in the host's immune system. However, more studies are needed to clarify this poorly understood cascade of events., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

We investigated how natural dissolved organic matter (DOM) of the Rio Negro (Amazon) affects acute copper (Cu) toxicity to local fish: the cardinal tetra (Paracheirodon axelrodi) and the dwarf cichlid (Apistogramma agassizii). It is established that Cu 2+ complexation with DOM decreases Cu bioavailability (and thus toxicity) to aquatic organisms, as conceptualized by the Biotic Ligand Model (BLM). However, we also know that Rio Negro's DOM can interact with fish gills and have a beneficial effect on Na + homeostasis, the main target of acute Cu toxicity in freshwater animals. We aimed to tease apart these potential protective effects of DOM against Cu-induced Na + imbalances in fish. In the laboratory, we acclimated fish to Rio Negro water (10 mg L -1 DOC) and to a low-DOM water (1.4 mg L -1 DOC) with similar ion composition and pH (5.9). We measured 3-h Cu uptake in gills and unidirectional and net Na + physiological fluxes across a range of Cu concentrations in both waters. Various DOM pre-acclimation times (0, 1 and 5 days) were evaluated in experiments with P. axelrodi. Copper exposure led to similar levels of net Na + loss in the two fish, but with distinct effects on Na + influx and efflux rates reflecting their different ionoregulation strategies. Rio Negro DOM protected against Cu uptake and toxicity in the two fish species. Both Cu uptake in fish gills and Na + regulation disturbances were relatively well predicted by the modelled aqueous free Cu 2+ ion concentration. These findings suggest that protection by DOM occurs mainly from Cu complexation under the tested conditions. The prevalence of this geochemical-type protection over a physiological-type protection agrees with the BLM conceptual framework, supporting the use of the BLM to assess the risk of Cu in these Amazonian waters., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The evolutionary and ontogenetic changes from water- to air-breathing result in major changes in the cardiorespiratory systems. However, the potential changes in hemoglobin's (Hb) oxygen binding properties during ontogenetic transitions to air-breathing remain poorly understood. Here we investigated Hb multiplicity and O 2 binding in hemolysates and Hb components from juveniles and adults of the obligate air-breathing pirarucu (Arapaima gigas) that starts life as water-breathing hatchlings. Contrasting with previous electrophoresis studies that report one or two isoHbs in adults, isoelectric focusing (IEF) resolved the hemolysates from both stages into four major bands, which exhibited identical O 2 binding properties (i.e. O 2 affinities, cooperativity coefficients, and sensitivities to pH and the major organic phosphate effectors), also as compared to the cofactor-free hemolysates. Of note, the multiplicity pattern recurred upon reanalyses of the most-abundant fractions isolated from the juvenile and the adult stages, suggesting possible stabilization of different quaternary states with different isoelectric points during the purification procedure. The study demonstrates unchanged Hb-O 2 binding properties during development, despite the pronounced differences in O 2 availability between the two media, which harmonizes with findings based on a broader spectrum of interspecific comparisons. Taken together, these results disclose that obligate air-breathing in Arapaima is not contingent upon changes in Hb multiplicity and O 2 binding characteristics., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Global climate change represents a critical threat to the environment since it influences organismic interactions, such as the host-parasite systems, mainly in ectotherms including fishes. Rising temperature and CO 2 are predicted to affect this interaction other and critical physiological processes in fish. Herein, we investigated the effects of different periods of exposure to climate change scenarios and to two degrees of parasitism by monogeneans in the host-parasite interaction, as well as the antioxidant and ionoregulatory responses of tambaqui (Colossoma macropomum), an important species in South American fishing and aquaculture. We hypothesized that temperature and CO 2 changes in combination with parasite infection would interfere with the host's physiological processes that are related to oxidative stress and ionoregulation. We experimentally exposed C. macropomum to low and high levels of parasitism in the current and extreme climate scenarios (4.5 °C and 900 ppm CO 2 above current levels) for periods of seven and thirty days and we use as analyzed factors; the exposure time, the climate scenario and parasitism level in a 2 × 2 × 2 factorial through a three-way ANOVA as being fish the experimental unit (n = 8). An analysis of gill enzymatic and gene expression profile was performed to assess physiological (SOD, GPx and Na + /K + -ATPase enzymes) and molecular (Nrf2, SOD1, HIF-1α and NKA α1a genes) responses. A clear difference in the parasitism levels of individuals exposed to the extreme climate scenario was observed with a rapid and aggressive increase that was higher after 7 days of exposure though showed a decrease after 30 days. The combination of exposure to the extreme climate change scenario and parasitism caused oxidative stress and osmoregulatory disturbance, which was observed through the analysis of gene expression (Nrf2, SOD1, HIF-1α and NKA α1a) and antioxidant and ionoregulatory enzymes (SOD, GPx and Na + /K + -ATPase) on the host, possibly linked to inflammatory processes caused by the high degree of parasitism. In the coming years, these conditions may result in losses of performance for this species, and as such will represent ecological damage and economical losses, and result in a possible vulnerability in relation to food security., (© 2021. The Author(s).)

Freshwater fish are restricted by their physiology to rivers and lakes, and are generally limited in their capacity to disperse across basins. As a result, there is often a close match between the evolutionary history of river basins and their natural history. Thus, the regional landscape and ecological features, such as temperature, have shaped the evolution and adaptation of local fish assemblages. Climate change is expected to affect fish diversity and increase extinction, especially in low latitudes, and it has been suggested that species that inhabit low latitude species are more susceptible since they live close to their maximum thermal limits and have low capacity for acclimation. To understand the mechanisms of variation in thermal tolerance across a broad-scale of South American fishes is fundamental to be able to assess the vulnerability of species and habitat to global warming. Herein, we present the first attempt to analyze the vulnerability of South American freshwater fish species, based on the review of upper thermal limits of 106 species from a broad range of latitudinal habitats. Our findings show that upper thermal limits decrease with latitude, while the thermal safety margin (TSM) increase. Furthermore, the latitude has little effects on the acclimation response ratio, and the TSM decreased with rising temperatures. These data suggest that thermal phenotypic acclimation has low potential for mitigating global warming. These results indicate that South American fish species living in tropical areas are more susceptible to global warming since they are already living close to their maximum habitat temperature., (© 2021 Wiley Periodicals LLC.)

The obligate air-breathing Amazonian fish, Arapaima gigas, hatch as water-breathing larvae but with development, they modify their swim bladder to an air-breathing organ (ABO) while reducing their gill filaments to avoid oxygen loss. Here, we show that significant changes already take place between 4 weeks (1.6 g) and 11 weeks (5 g) post hatch, with a reduction in gill lamellar surface area, increase in gill diffusion distance, and proliferation of the parenchyma in the ABO. By using a variety of methods, we quantified the surface area and diffusion distances of the gills and skin, and the swim bladder volume and anatomical complexity from hatch to 11-week-old juveniles. In addition, we identified the presence of two ionocyte types in the gills and show how these change with development. Until 1.6 g, A. gigas possess only the H + -excreting/Na + -absorbing type, while 5-g fish and adults have an additional ionocyte which likely absorbs H + and Cl - and excretes HCO 3 - . The ionocyte density on the gill filaments increased with age and is likely a compensatory mechanism for maintaining ion transport while reducing gill surface area. In the transition from water- to air-breathing, A. gigas likely employs a trimodal respiration utilizing gills, skin, and ABO and thus avoid a respiratory-ion regulatory compromise at the gills., (© 2021 Wiley Periodicals LLC.)

Although blackwaters, named for their rich content of dissolved organic carbon (DOC), are often very poor in ions and very acidic, they support great fish biodiversity. Indeed, about 8% of all freshwater fish species live in the blackwaters of the Rio Negro watershed in the Amazon basin. We review how native fish survive these harsh conditions that would kill most freshwater fish, with a particular focus on the role of DOC, a water quality parameter that has been relatively understudied. DOC, which is functionally defined by its ability to pass through a 0.45-µm filter, comprises a diverse range of compounds formed by the breakdown of organic matter and is quantified by its carbon component that is approximately 50% by mass. Adaptations of fish to acidic blackwaters include minimal acid-base disturbances associated with a unique, largely unknown, high-affinity Na + uptake system that is resistant to inhibition by low pH in members of the Characiformes, and very tight regulation of Na + efflux at low pH in the Cichliformes. Allochthonous (terrigenous) DOC, which predominates in blackwaters, consists of larger, more highly colored, reactive molecules than autochthonous DOC. The dissociation of protons from allochthonous components such as humic and fulvic acids is largely responsible for the acidity of these blackwaters, yet at the same time, these components may help protect organisms against the damaging effects of low water pH. DOC lowers the transepithelial potential (TEP), mitigates the inhibition of Na + uptake and ammonia excretion, and protects against the elevation of diffusive Na + loss in fish exposed to acidic waters. It also reduces the gill binding and toxicity of metals. At least in part, these actions reflect direct biological effects of DOC on the gills that are beneficial to ionoregulation. After chronic exposure to DOC, some of these protective effects persist even in the absence of DOC. Two characteristics of allochthonous DOC, the specific absorbance coefficient at 340 nm (determined optically) and the PBI (determined by titration), are indicative of both the biological effectiveness of DOC and the ability to protect against metal toxicity. Future research needs are highlighted, including a greater mechanistic understanding of the actions of DOCs on gill ionoregulatory function, morphology, TEP, and metal toxicity. These should be investigated in a wider range of native fish Orders that inhabit one of the world's greatest biodiversity hotspots for freshwater fishes., (© 2021 Wiley Periodicals LLC.)

Tambaqui, a species native to the Amazon and Orinoco Basins and their tributaries, has a history marked by biological resilience that makes this species a model for studies focused on ecology, physiology, and fish farming. In addition, it is of economic interest, due to its favorable characteristics for production in farms and its unique flavor. As the tambaqui responds in a unique way to several environmental disturbances of natural origin, the species is often used in environmental studies. Some of these studies have been revisited in this review. We revised aspects related to its natural history, habitats and geographic distribution, physiological and biochemical adaptations, and zootechnical performance. The extraordinary adaptation of the tambaqui is the fast expansion of its lower lip when exposed to low oxygen availability that is improved simultaneously with other adjustments. The resilience of this species to significant alterations in water pH is also surprising, and is incomparable with that of other species, as only when it is exposed to pH 3.5, does the tambaqui begin to present physiological-biochemical disturbances. The analysis of the gene expression of tambaqui specimens under different experimental conditions has shed light on the adaptive mechanisms used by this unique Amazonian species. In this sense, this review sought to gather information regarding the tambaqui, and its many biological features employed to survive environmental challenges., (© 2021 Wiley Periodicals LLC.)

Previous studies have suggested that the capacity of natural dissolved organic carbon (DOC) molecules to interact with biological membranes is associated with their aromaticity (SAC 340 ); origin (allochthonous versus autochthonous, FI); molecular weight (Abs 254/365 ); and relative fluorescence of DOC moieties (PARAFAC analysis). These interactions may be especially important when fish are challenged by acidic waters, which are known to inhibit the active uptake of Na + and Cl - , while stimulating diffusive ion losses in freshwater fishes. Therefore, zebrafish were acclimated (7 days, pH 7.0) to five natural DOC sources (10 mg C/L), two from the Amazon Basin and three from Canada, together with a "no-added DOC" control. After the acclimation, fish were challenged by exposure to acidic water (pH 4.0) for 3 h. Osmoregulatory parameters were measured at pH 7.0 and 4.0. Acclimation to the five DOC sources did not disturb Na + , Cl - and ammonia net fluxes, but resulted in differential elevations in Na + , K + ATPase and v-type H + ATPase activities in fish at pH 7.0. However, after transfer to pH.4.0, the control fish exhibited rapid increases in both enzymes. In contrast the DOC- acclimated animals exhibited unchanged (Na + , K + ATPase) or differentially increased (v-type H + ATPase) activities. Na + , Cl - and ammonia net fluxes remained unchanged in the control fish, but were differentially elevated in most of the DOC treatments at pH 4.0, relative to the same DOC treatments at pH 7.0. Correlations between the osmoregulatory data the DOCs properties highlight that the DOC properties drive different effects on gill physiology., (© 2021 Wiley Periodicals LLC.)

Critical thermal maximum (CT max ) is often used as an index of upper thermal tolerance in fishes; however, recent studies have shown that some fishes exhibit agitation or avoidance behavior well before the CT max is reached. In this study, we quantified behavioral changes during CT max trials in two Amazonian cichlids, Apistogramma agassizii and Mesonauta insignis. The thermal agitation temperature (T ag ) was recorded as the temperature at which fish left cover and began swimming in an agitated manner, and four behaviors (duration of sheltering, digging, activity, and aquatic surface respiration [ASR]) were compared before and after T ag . Both A. agassizii and M. insignis exhibited high critical thermal maxima, 40.8°C and 41.3°C, respectively. Agitation temperature was higher in M. insignis (37.3°C) than in A. agassizii (35.4°C), indicating that A. agassizii has a lower temperature threshold at which avoidance behavior is initiated. Activity level increased and shelter use decreased with increased temperatures, and patterns were similar between the two species. Digging behavior increased after T ag in both species, but was higher in A. agassazii and may reflect its substrate-oriented ecology. ASR (ventilating water at the surface film) was extremely rare before T ag , but increased in both cichlid species after T ag and was greater in M. insignis than in A. agassizii. This suggests that fish were experiencing physiological hypoxia at water temperatures approaching CT max . These results demonstrate that acute thermal challenge can induce a suite of behavioral changes in fishes that may provide additional, ecologically relevant information on thermal tolerance., (© 2021 Wiley Periodicals LLC.)

The tambaqui (Colossoma macropomum), migrates annually between whitewater and blackwater rivers of the Amazon. Unlike the whitewater, blackwater is characterized by higher levels of dissolved organic carbon (DOC), including humic acids (HA). Because humic substances impair sensory processes, the current study tested the hypothesis that O 2 and/or CO 2 chemoreception is impeded in blackwater owing to the presence of HA. Thus, the ventilatory responses of tambaqui to hypoxia or hypercapnia were assessed in well water transported from Manaus, local blackwater, and in well water containing HA either extracted from Rio Negro water or obtained commercially (Sigma Aldrich; SA). In well water, tambaqui exhibited typical hyperventilatory responses to hypoxia or hypercapnia. These responses were prevented by simultaneously exposing fish to SA HA (20 mg l -1 ). The negative effects of SA HA on ventilation were prevented when natural DOC (30 mg l -1 ; extracted from Rio Negro water after first removing the endogenous HA fraction) was added concurrently, indicating a protective effect of this non-humic acid DOC fraction. The hyperventilatory responses were unaffected during acute exposure or after acclimation of fish to Rio Negro water. HA extracted from Rio Negro water did not impair the hyperventilatory responses to hypoxia or hypercapnia. This study, while demonstrating a negative effect of SA HA derived from peat (coal) on the control of breathing in tambaqui, failed to reveal any detrimental consequences of HA (derived from the decomposition of a variety of lignin-rich plants) naturally occurring in the blackwaters of the Rio Negro., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Light energy and oxygen drive photo-oxidation of dissolved organic carbon (DOC). The longer the wavelength the greater its depth of penetration into water, changing the spectral environment with depth. We asked how oxygen concentration and light spectral composition might affect photo-oxidation processes in DOC. Outdoor experiments compared responses of fluorescence and absorbance indices to photo-oxidation of filtered (0.45 µm) Rio Negro water (Amazon Basin) under near-anoxia, normoxia and hyperoxia exposed to natural sunlight or reduced sunlight (≥340, reduced-UVR). Near-anoxia decreased all absorbance and fluorescence indices. Absorbance changed across the spectrum (≥250 nm) even under reduced-UVR provided that oxygen was present. This phenomenon maintains broader photo-oxidation and the release of CO 2 at depth. Slope 350-400 was responsive to changes in the irradiance field but not to oxygen concentration, while Slope 275-295 responded to both. Thus, larger molecules are broken down near the water's surface and medium to smaller molecules continue to be processed at depth. The production of fulvic acid-like fluorescence required both UVB and oxygen, restricting its production to surface waters. The relatively small increase in R 254/365 compared with the loss of SUVA 254 under near-anoxia indicated a slower breakdown of larger DOC molecules as oxygen becomes limiting. Breakdown of larger molecules which absorb in the 350-400 nm range, appears to involve two steps - one by radiant energy and another involving oxygen. The study results reflect the dynamic gradients in photo-oxidation with depth., (Copyright © 2021. Published by Elsevier Ltd.)

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., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Boron oxide nanoparticles (nB 2 O 3 ) are manufactured for structural, propellant, and clinical applications and also form spontaneously through the degradation of bulk boron compounds. Bulk boron is not toxic to vertebrates but the distinctive properties of its nanostructured equivalent may alter its biocompatibility. Few studies have addressed this possibility, thus our goal was to gain an initial understanding of the potential acute toxicity of nB 2 O 3 to freshwater fish and we used a variety of model systems to achieve this. Bioactivity was investigated in rainbow trout ( Oncorhynchus mykiss ) hepatocytes and at the whole animal level in three other North and South American fish species using indicators of aerobic metabolism, behavior, oxidative stress, neurotoxicity, and ionoregulation. nB 2 O 3 reduced O. mykiss hepatocyte oxygen consumption ( Ṁ O 2 ) by 35% at high doses but whole animal Ṁ O 2 was not affected in any species. Spontaneous activity was assessed using Ṁ O 2 frequency distribution plots from live fish. nB 2 O 3 increased the frequency of high Ṁ O 2 events in the Amazonian fish Paracheirodon axelrodi , suggesting exposure enhanced spontaneous aerobic activity. Ṁ O 2 frequency distributions were not affected in the other species examined. Liver lactate accumulation and significant changes in cardiac acetylcholinesterase and gill Na + /K + -ATPase activity were noted in the north-temperate Fundulus diaphanus exposed to nB 2 O 3 , but not in the Amazonian Apistogramma agassizii or P. axelrodi . nB 2 O 3 did not induce oxidative stress in any of the species studied. Overall, nB 2 O 3 exhibited modest, species-specific bioactivity but only at doses exceeding predicted environmental relevance. Chronic, low dose exposure studies are required for confirmation, but our data suggest that, like bulk boron, nB 2 O 3 is relatively non-toxic to aquatic vertebrates and thus represents a promising formulation for further development., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 MacCormack, Gormley, Khuong, Adams, Braz-Mota, Duarte, Vogels, Tremblay, Val, Almeida-Val and Westcott.)

Tambaqui (Colossoma macropomum) are a model species for tropical fish physiology, but details are lacking about their ionoregulatory response to acid waters. To provide specifics, we measured unidirectional Na + fluxes in low pH waters. Sodium influx ([Formula: see text]) was uninhibited during acute exposure to pH 4.5 and 3.5, and Na efflux ([Formula: see text]) rose only slightly at pH 3.5; net Na + flux ([Formula: see text]) remained positive at all pH. Similarly, during 24 h transfer to pH 3.5 [Formula: see text], [Formula: see text], and [Formula: see text] were unchanged at all times. Taking a closer look at the mechanism of Na + transport in the gills of tambaqui we found that [Formula: see text] was uninhibited by HMA, a Na + /H + -exchanger blocker, and Benzamil, a Na + -channel inhibitor, casting doubt on their role in Na + uptake in this fish. Measurement of Na + /K + -ATPase (NKA) and H + -ATPase (VHA) activity showed that neither changed at low pH compared to measurements at pH 6.5. Western blot analysis of ATPase expression saw no changes in amount of NKA and VHA at low pH, and immunohistochemistry showed expression of both NKA and VHA on lamellae and interlamellar region of tambaqui gills and that both proteins co-localized to the same gill cells. Location of expression also did not change in low pH water. Amazingly, tambaqui seem unaffected by pH 3.5 water, making them one of the most acid-tolerant fish species examined so far. In addition, they appear to share key ionoregulatory traits with other fish of the order Characiformes, which suggest a common origin for the ionoregulatory attributes.

The Amazonian aquatic ecosystem undergoes seasonal variations and daily changes that directly affect the availability of oxygen. During the day the levels of oxygen can reach supersaturation, and at night can drop to zero. In this way, aquatic organisms are exposed daily to physiological challenges regarding the availability of oxygen. The present study revealed significant differences in the physiology and performance of two cichlids: Geophagus proximus (black water cichlid - from Negro River) and Chaetobranchopsis orbicularis (white water cichlid - from Amazon River), exposed to hypoxia. The white water cichlid showed lower value (1.99 ± 0.79 pKa) of critical pressure of oxygen (Pcrit) and a longer time (68.00 ± 14.11 min) for total loss of balance (LOE); however, this species showed 50% mortality during exposure to hypoxia, while the black water cichlid did not show mortality. Both cichlids presented a decrease in O 2 consumption rate (OCR) during hypoxia.. In this sense, it was observed that the black water cichlid presented several physiological strategies during hypoxia, such as, a significant increase in plasma cortisol levels, nucleoside triphosphate diphosphohydrolase activity (for adenosine diphosphate (ADP) as a substrate) in the gills, and the activity of adenosine deaminase (ADA) in gills and liver, in addition to a significant increase in the activity of complexes (II-III) in the transporter chain of electrons in both analyzed tissues and succinate dehydrogenase activity of gills' mitochondria. On the other hand, the only physiological change observed in the white water cichlid was a significant reduction in the activity of complexes II-III in gills and liver. Based on our findings, we can hypothesize that the white water cichlid specie has less tolerant to hypoxia when compared to the black water cichlid., (Copyright © 2021. Published by Elsevier Inc.)

The contamination of aquatic environments by transition metals can have a direct influence on the reproductive process of several organisms in the aquatic biota. This study aimed to evaluate the effect of cadmium and copper on the sperm of tambaqui (Colossoma macropomum). Male (n = 4) and female (n = 4) specimens of C. macropomum were induced to spermiation and ovulation, with sperm being activated in the following media: 0; 0.6; 1.2 and 1.8 mg/L of cadmium (CdCl 2 ) and 0; 0.4; 0.8 and 1.2 mg/L of copper (CuCl 2 ). Sperm quality was assessed through time (s) and motility rate (%), superoxide dismutase (SOD) and glutathione S-transferase (GST) activities, lipoperoxidation levels (LPO), and morphological characteristics. In parallel, the effects of these metals on the rate of fertilization and hatching of the oocytes were evaluated. The duration and motility rate of sperm were longer in the control treatment, 85.67 ± 11.01 s; 90 ± 0.01%, and progressively decreased to 44.67 ± 4.16 s and 60 ± 5%, respectively, in concentrations of 1.8 mg/L (44.67 ± 4.16 s; 60 ± 5%) of CdCl 2 and to 65.67 ± 3.30 s; 70 ± 5%, respectively, in concentrations of 0.8 mg/L of CuCl 2 . We observed an increase in the activity of the SOD enzyme in sperm cells exposed to 1.2 mg/L of CdCl 2 . The LPO levels were increased significantly in sperm cells exposed to 1.2 and 1.8 mg/L of CdCl 2 and 0.8 mg/L of CuCl 2 . Fertilization and hatching were severely impaired in the presence of Cd and Cu. These data indicate that environments contaminated with cadmium and copper harm the gametes of C. macropomum., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The Amazon basin contains more than 20% of the world's freshwater fishes, many of ecological and economical importance. An increase in temperature of 2.2 to 7 °C is predicted to occur within the next century in the worst-case scenario of climate change predictions, which will likely be associated with an increase in the prevalence and duration of reduced water oxygen levels (hypoxia). Furthermore, there is an increasing frequency of heat waves in the Amazon basin, which exacerbates issues related to temperature and hypoxia. Increases in temperature and hypoxia both constrain an organism's ability to supply oxygen to metabolizing tissues, thus the ability to cope with thermal and hypoxic stress may be correlated. Here, we reveal a positive correlation between acute thermal tolerance and acute hypoxia tolerance amongst 37 Amazonian fish species at the current river temperatures of 28-31 °C. The effects of long-term (10 days or 4 weeks) increases in temperature were investigated in a subset of 13 species and demonstrated that 2 species failed to acclimate and survive at 33 °C, 9 species failed at 35 °C, and only 2 species survived up to 35 °C. Of those that survived long-term exposure to 33 or 35 °C, the majority of the species demonstrated only an improvement in acute thermal tolerance. In contrast, hypoxia tolerance was reduced following acute- and long-term exposure to 33, 35 or 37 °C in all species investigated. The results of this study suggest that many of the fish species that inhabit the Amazon may be at risk during both short- and long-term temperature increases and these risks are exacerbated by the associated environmental hypoxia., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper “Reduced hypoxia tolerance and survival at elevated temperatures may limit the ability of Amazonian fishes to survive in a warming world.”, (Copyright © 2020 Elsevier B.V. All rights reserved.)

The toxic effects of copper (Cu) are linked to dysfunction of metabolism and depletion of adenosine triphosphate (ATP). Nevertheless, the effects related to phosphoryl transfer network, a network of enzymes to precise coupling of the ATP-production and ATP-consuming process for maintenance of bioenergetic, remain unknown. Therefore, the aim of this study was to determine whether the phosphoryl transfer network could be one pathway involved in the bioenergetic imbalance of Cichlasoma amazonarum exposed for 96 h to environmentally relevant concentrations of Cu found in Amazonia water around mines. Branchial mitochondrial creatine kinase (CK) activity was significantly lower in fish exposed to 1500 μg/L Cu than in the control group, while branchial cytosolic CK activity was significantly greater. Branchial (exposed to 750 and 1500 μg/L Cu) and hepatic (exposed to 1500 μg/L Cu) pyruvate kinase (PK) activity was significantly lower in fish exposed to Cu than in the control group. Branchial and hepatic ATP levels were significantly lower in fish exposed to 1500 μg/L than in the control group. Branchial reactive oxygen species (ROS) and lipid peroxidation (LPO) levels were significantly higher in fish exposed to 750 and 1500 μg/L Cu compared to control. Hepatic ROS and LPO levels were significantly higher in fish exposed to 1500 μg/L than in the control group. Branchial and hepatic Cu levels were significantly higher in fish exposed to 1500 μg/L compared to other groups. Exposure to 750 and 1500 μg/L Cu impairs bioenergetics homeostasis, which appears to be mediated by ROS overproduction and lipid peroxidation., Competing Interests: Declaration of competing interest None., (Copyright © 2020 Elsevier Inc. All rights reserved.)