A Review of Freshwater Invertebrates as Biomonitors of Methylmercury: the Importance of More Complete Physical and Chemical Reporting.

Methylmercury (MeHg) is a toxic and bioaccumulative organo-metallic compound that is naturally produced in many ecosystems. Organisms that occupy the lower trophic positions in food webs may be key factors in the assessment of MeHg biomagnification between ecosystems. Here we present a review of the peer-reviewed literature examining MeHg bioaccumulation in freshwater invertebrates, focused principally on insects. This review aims to characterize the invertebrates that bioaccumulate higher MeHg concentrations and therefore pose a higher risk to upper trophic levels and to clarify which ecosystems are more susceptible to bioaccumulation in lower trophic levels. However, we found that few studies provided robust environmental data (notably water chemistry) as part of their papers, dramatically limiting our ability to test for factors that might contribute to different concentrations of MeHg in invertebrates. We highlight the importance of providing physical and chemical characteristics of study sites in publications examining MeHg bioaccumulation and biomagnification. Adopting the proposed recommendations will improve the available information for future mercury risk assessment analyses.

Optimization of microbial detoxification for an aquatic mercury-contaminated environment.

Mercury (Hg) reduction performed by microorganisms is well recognized as a biological means for remediation of contaminated environment. Recently, studies demonstrated that Hg-resistant microorganisms of Tagus Estuary are involved in metal reduction processes. In the present study, aerobic microbial community isolated from a highly Hg-contaminated area of Tagus Estuary was used to determine the optimization of the reduction process in conditions such as the contaminated ecosystem. Factorial design methodology was employed to examine the influence of glucose, sulfate, iron, and chloride on Hg reduction. In the presence of several concentrations of these elements, microbial community reduced Hg in a range of 37-61% of the initial 0.1 mg/ml Hg2+ levels. The response prediction through central composite design showed that the increase of sulfate concentration led to an optimal response in Hg reduction by microbial community, while the rise in chloride levels markedly decreased metal reduction. Iron may exert antagonistic effects depending upon the media composition. These results are useful in understanding the persistence of Hg contamination in Tagus Estuary after inactivation of critical industrial units, as well as data might also be beneficial for development of new bioremediation strategies either in Tagus Estuary and/or in other Hg-contaminated aquatic environments.

Aerobic Mercury-resistant bacteria alter Mercury speciation and retention in the Tagus Estuary (Portugal).

Aerobic mercury-resistant bacteria were isolated from the sediments of two highly mercury-polluted areas of the Tagus Estuary (Barreiro and Cala do Norte) and one natural reserve area (Alcochete) in order to test their capacity to transform mercury. Bacterial species were identified using 16S rRNA amplification and sequencing techniques and the results indicate the prevalence of Bacillus sp. Resistance patterns to mercurial compounds were established by the determination of minimal inhibitory concentrations. Representative Hg-resistant bacteria were further tested for transformation pathways (reduction, volatilization and methylation) in cultures containing mercury chloride. Bacterial Hg-methylation was carried out by Vibrio fluvialis, Bacillus megaterium and Serratia marcescens that transformed 2-8% of total mercury into methylmercury in 48h. In addition, most of the HgR bacterial isolates showed Hg(2+)-reduction andHg(0)-volatilization resulting 6-50% mercury loss from the culture media. In summary, the results obtained under controlled laboratory conditions indicate that aerobic Hg-resistant bacteria from the Tagus Estuary significantly affect both the methylation and reduction of mercury and may have a dual face by providing a pathway for pollution dispersion while forming methylmercury, which is highly toxic for living organisms.

Isolation and characterization of mercury-resistant bacteria from sediments of Tagus Estuary (Portugal): implications for environmental and human health risk assessment.

Mercury (Hg) contamination of aquatic systems has been recognized as a global and serious problem affecting both human and environmental health. In the aquatic ecosystems, mercurial compounds are microbiologically transformed with methylation responsible for generation of methylmercury (MeHg) and subsequent biomagnification in food chain, consequently increasing the risk of poisoning for humans and wildlife. High levels of Hg, especially MeHg, are known to exist in Tagus Estuary as a result of past industrial activities. The aim of this study was to isolate and characterize Hg-resistant bacteria from Tagus Estuary. Mercury-resistant (Hg-R) bacteria were isolated from sediments of two hotspots (Barreiro and North Channel) and one reserve area (Alcochete). Mercury contamination in these areas was examined and bacterial susceptibility to Hg compounds evaluated by determination of minimal inhibitory concentrations (MIC). The isolates characterization was based on morphological observation and biochemical testing. Bacteria characteristics, distribution, and Hg resistance levels were compared with metal levels. Barreiro and North Channel were highly contaminated with Hg, containing 126 and 18 µg/g total Hg, respectively, and in Alcochete, contamination was lower at 0.87 µg/g total Hg. Among the isolates there were aerobic and anaerobic bacteria, namely, sulfate-reducing bacteria, and Hg resistance levels ranged from 0.16 to 140 µg/ml for Hg(2+) and from 0.02 to 50.1 µg/ml for MeHg. The distribution of these bacteria and the resistance levels were consistent with Hg contamination along the depth of the sediments. Overall, results show the importance of the characterization of Tagus Estuary bacteria for ecological and human health risk assessment.

Mercury-resistant bacteria from salt marsh of Tagus Estuary: the influence of plants presence and mercury contamination levels.

Mercury (Hg) contamination of aquatic systems has been recognized as a global, serious problem affecting both wildlife and humans. High levels of Hg, in particular methylmercury (MeHg), were detected in surface sediments of Tagus Estuary. MeHg is neurotoxic and its concentration in aquatic systems is dependent upon the relative efficiency of reduction, methylation, and demethylation processes, which are mediated predominantly by the microbial community, in particular mercury-resistant (HgR) bacteria. Plants in contaminated ecosystems are known to take up Hg via plant roots. Therefore, the aims of this study were to (1) isolate and characterize HgR bacteria from a salt marsh of Tagus Estuary (Rosário) and (2) determine HgR bacteria levels in the rhizosphere and, consequently, their influence in metal cycling. To accomplish this objective, sediments samples were collected during the spring season in an area colonized by Sacocornia fruticosa and Spartina maritima and compared with sediments without plants. From these samples, 13 aerobic HgR bacteria were isolated and characterized morphologically, biochemically, and genetically, and susceptibility to Hg compounds, Hg(2+), and MeHg was assessed by determination of minimal inhibitory concentration (MIC). Genetically, the mer operon was searched by polymerase chain reaction (PCR) and 16S rRNA sequencing was used for bacterial identification. Results showed that the isolates were capable of growing in the presence of high Hg concentration with MIC values for HgCl2 and MeHgCl in the ranges of 1.7-4.2 µg/ml and 0.1-0.9 µg/ml, respectively. The isolates from sediments colonized with Sacocornia fruticosa displayed higher resistance levels compared to ones colonized with Spartina maritima. Bacteria isolates showed different capacity of Hg accumulation but all displayed Hg volatilization capabilities (20-50%). Mer operon was found in two isolates, which genetically confirmed their capability to convert Hg compounds by reducing them to Hg(0). Thus, these results are the first evidence of the relevance of interaction between bacteria and plants in Hg cycling in Tagus Estuary.

Redox Homeostasis Disclosed in the Saltmarsh Plant Halimione portulacoides upon Short Waterborne Exposure to Inorganic Mercury.

The saltmarsh plant Halimione portulacoides was shortly exposed to realistic levels of inorganic mercury (iHg) with the aim of investigating the adaptative processes of the roots and leaves regarding redox homeostasis, physiology, and Hg accumulation. Plants were collected at a contaminated (CONT) and a reference (REF) site to address the interference of contamination backgrounds. The influence of major abiotic variables (i.e., temperature and light) was also examined. Total Hg levels, antioxidant enzymes, lipid peroxidation (LPO), and photosynthetic activity were analyzed after 2 and 4 h of exposure. A poor accumulation of Hg in the roots was noticed, and no translocation to the stems and leaves was found, but plants from the CONT site seemed more prone to iHg uptake (in winter). Despite this, antioxidant modulation in the roots and leaves was found, disclosing, in winter, higher thresholds for the induction of enzymatic antioxidants in CONT leaves compared to REF plants, denoting that the former are better prepared to cope with iHg redox pressure. Consistently, CONT leaves exposed to iHg had remarkably lower LPO levels. Exposure did not impair photosynthetic activity, pinpointing H. portulacoides' ability to cope with iHg toxicity under very-short-term exposure. Biochemical changes were noticed before enhancements in accumulation, reinforcing the relevance of these responses in precociously signaling iHg toxicity.

Spectroscopic Detection of Biosignatures in Natural Ice Samples as a Proxy for Icy Moons.

Some of the icy moons of the solar system with a subsurface ocean, such as Europa and Enceladus, are the targets of future space missions that search for potential extraterrestrial life forms. While the ice shells that envelop these moons have been studied by several spacecrafts, the oceans beneath them remain unreachable. To better constrain the habitability conditions of these moons, we must understand the interactions between their frozen crusts, liquid layers, and silicate mantles. To that end, astrobiologists rely on planetary field analogues, for which the polar regions of Earth have proven to be great candidates. This review shows how spectroscopy is a powerful tool in space missions to detect potential biosignatures, in particular on the aforementioned moons, and how the polar regions of the Earth are being used as planetary field analogues for these extra-terrestrial environments.

Biomarkers of adverse response to mercury: histopathology versus thioredoxin reductase activity.

Exposure to mercury is normally assessed by measuring its accumulation in hair, blood or urine. Currently, the biomarkers of effect that have been proposed for mercurials, such as coproporphyrines or oxidative stress markers, are not sensitive enough and lack specificity. Selenium and selenoproteins are important targets for mercury and thioredoxin reductase (TrxR) in particular was shown to be very sensitive to mercury compounds both in vitro and in vivo. In this study we looked into the relation between the inhibition of thioredoxin reductase (TrxR) activity and histopathological changes caused by exposure to mercurials. Juvenile zeabra-seabreams were exposed to Hg(2+) or MeHg for 28 days and histopathological changes were analyzed in the liver and kidney as well as TrxR activity. Both mercurials caused histopathological changes in liver and kidney, albeit Hg(2+) caused more extensive and severe lesions. Likewise, both mercurials decreased TrxR activity, being Hg(2+) a stronger inhibitor. Co-exposure to Hg(2+) and Se fully prevented TrxR inhibition in the liver and reduced the severity of lesions in the organ. These results show that upon exposure to mercurials, histopathological alterations correlate with the level of TrxR activity and point to the potential use of this enzyme as a biomarker of mercury toxicity.

Biogeochemistry of mercury and methylmercury in sediment cores from Sundarban mangrove wetland, India--a UNESCO World Heritage Site.

This study was performed to elucidate the distribution, concentration trend and possible sources of total mercury (Hg(T)) and methylmercury (MeHg) in sediment cores (<63 µm particle size; n = 75) of Sundarban mangrove wetland, northeastern part of the Bay of Bengal, India. Total mercury was determined by atomic absorption spectrometry (AAS) in a Leco AMA 254 instrument and MeHg by gas chromatography-atomic fluorescence spectrometry (GC-AFS). A wide range of variation in Hg(T) (0.032-0.196 µg g(-1) dry wt.) as well as MeHg (0.04-0.13 ng g(-1) dry wt.) concentrations revealed a slight local contamination. The prevalent low Hg(T) levels in sediments could be explained by sediment transport by the tidal Hugli (Ganges) River that would dilute the Hg(T) values via sediment mixing processes. A broader variation of MeHg proportions (%) were also observed in samples suggesting that other environmental variables such as organic carbon and microbial activity may play a major role in the methylation process. An overall elevated concentration of Hg(T) in surface layers (0-4 cm) of the core is due to remobilization of mercury from deeper sediments. Based on the index of geoaccumulation (I (geo)) and low effects-range (ER-L) values, it is considered that the sediment is less polluted by Hg(T) and there is less ecotoxicological risk. The paper provides the first information of MeHg in sediments from this wetland environment and the authors strongly recommend further examination of Hg(T) fluxes for the development of a detailed coastal MeHg model. This could provide more refine estimates of a total flux into the water column.

A face detection ensemble to monitor the adoption of face masks inside the public transportation during the COVID-19 pandemic.

The designing of ensembles is widely adopted when single machine learning methods fail to obtain satisfactory performances by analyzing complex data characterized by being imbalanced, high-dimensional, and noisy. Such a failure is a well-known statistical challenge when the learning algorithm searches for a model in a large space of hypotheses and the data do not significantly represent the problem, thus not inducing it from a space of admissible functions towards the best global model. We have addressed this issue in a real-world application, whose main objective was to identify whether users were wearing masks inside public transportation during the COVID-19 pandemic. Several studies have already pointed that face masks are an important and efficient non-pharmacological strategy to reduce the virus spread. In this sense, we designed an approach using Convolutional Neural Networks (CNN) to track the adoption of masks in different transportation lines, regions, days, and time. Aiming at reaching this goal, we propose an ensemble of face detectors and a CNN architecture, called MaskNet, to analyze all public-transport passengers and provide valuable information to policymakers, which are able to dedicate efforts to more effective advertisements and awareness work. In practice, our approach is running in a real scenario in Salvador (Brazil).

Contamination analysis of Arctic ice samples as planetary field analogs and implications for future life-detection missions to Europa and Enceladus.

Missions to detect extraterrestrial life are being designed to visit Europa and Enceladus in the next decades. The contact between the mission payload and the habitable subsurface of these satellites involves significant risk of forward contamination. The standardization of protocols to decontaminate ice cores from planetary field analogs of icy moons, and monitor the contamination in downstream analysis, has a direct application for developing clean approaches crucial to life detection missions in these satellites. Here we developed a comprehensive protocol that can be used to monitor and minimize the contamination of Arctic ice cores in processing and downstream analysis. We physically removed the exterior layers of ice cores to minimize bioburden from sampling. To monitor contamination, we constructed artificial controls and applied culture-dependent and culture-independent techniques such as 16S rRNA amplicon sequencing. We identified 13 bacterial contaminants, including a radioresistant species. This protocol decreases the contamination risk, provides quantitative and qualitative information about contamination agents, and allows validation of the results obtained. This study highlights the importance of decreasing and evaluating prokaryotic contamination in the processing of polar ice cores, including in their use as analogs of Europa and Enceladus.

Color Catalogue of Life in Ice: Surface Biosignatures on Icy Worlds.

With thousands of discovered planets orbiting other stars and new missions that will explore our solar system, the search for life in the universe has entered a new era. However, a reference database to enable our search for life on the surface of icy exoplanets and exomoons by using records from Earth's icy biota is missing. Therefore, we developed a spectra catalogue of life in ice to facilitate the search for extraterrestrial signs of life. We measured the reflection spectra of 80 microorganisms-with a wide range of pigments-isolated from ice and water. We show that carotenoid signatures are wide-ranged and intriguing signs of life. Our measurements allow for the identification of such surface life on icy extraterrestrial environments in preparation for observations with the upcoming ground- and space-based telescopes. Dried samples reveal even higher reflectance, which suggests that signatures of surface biota could be more intense on exoplanets and moons that are drier than Earth or on environments like Titan where potential life-forms may use a different solvent. Our spectra library covers the visible to near-infrared and is available online. It provides a guide for the search for surface life on icy worlds based on biota from Earth's icy environments.

Structural shifts in sea ice prokaryotic communities across a salinity gradient in the subarctic.

Current knowledge of the processes that shape prokaryotic community assembly in sea ice across polar ecosystems is scarce. Here, we coupled culture-dependent (bacterial isolation on R2A medium) and culture-independent (high-throughput 16S rRNA gene sequencing) approaches to provide the first comprehensive assessment of prokaryotic communities in the late winter ice and its underlying water along a natural salinity gradient in coastal Hudson Bay, an iconic cryo-environment that marks the ecological transition between Canadian Subarctic and Arctic biomes. We found that prokaryotic community assembly processes in the ice were less selective at low salinity since typical freshwater taxa such as Frankiales, Burkholderiales, and Chitinophagales dominated both the ice and its underlying water. In contrast, there were sharp shifts in community structure between the ice and underlying water samples at sites with higher salinity, with the orders Alteromonadales and Flavobacteriales dominating the ice, while the abovementioned freshwater taxa dominated the underlying water communities. Moreover, primary producers including Cyanobium (Cyanobacteria, Synechococcales) may play a role in shaping the ice communities and were accompanied by known Planctomycetes and Verrucomicrobiae taxa. Culture-dependent analyses showed that the ice contained pigment-producing psychrotolerant or psychrophilic bacteria from the phyla Proteobacteria, Actinobacteriota, and Bacteroidota, likely favored by the combination of low temperatures and the seasonal increase in sunlight. Our findings suggest that salinity, photosynthesis and dissolved organic matter are the main drivers of prokaryotic community structure in the late winter ice of coastal Hudson Bay, the ecosystem with the fastest sea ice loss rate in the Canadian North.

Inhibition of the thioredoxin system in the brain and liver of zebra-seabreams exposed to waterborne methylmercury.

Mercury compounds were recently found to interact in vitro with the thioredoxin system, inhibiting both Thioredoxin (Trx) and Thioredoxin reductase (TrxR). In order to evaluate if Trx and TrxR are affected in vivo by methylmercury (MeHg), we exposed juvenile zebra-seabreams to different concentrations of this toxicant in water for 28days followed by a 14-day depuration period. Methylmercury accumulated to a larger extent in the kidney and liver of fishes, but decreased significantly during the depuration. During the exposure, MeHg percentage in the liver reached levels above 90% of total mercury (HgT) decreasing to 60% of HgT by the end of the depuration period. In the kidney, MeHg accounted for 50-70% of HgT. In the brain and muscle, mercury accumulated throughout the exposure with all mercury being MeHg. The total mercury kept increasing in these organs during the depuration period. However, in the brain, this increase in HgT was accompanied by a decrease in the MeHg percentage (~10%). In the liver, both Trx and TrxR activities were significantly reduced (TrxR--40%; Trx--70%) by the end of the exposure, but recovered to control levels (100%) during the depuration. In the brain, both enzymes where inhibited during the depuration period (TrxR--75%; Trx--70%) when some production of inorganic mercury was detected. Activity of glutathione reductase showed increased levels when TrxR activity was low, suggesting complementarity between both systems. These results indicate that in vivo the thioredoxin system is a toxicological target for MeHg with TrxR being particularly affected.

Mercury methylation rates in Deception Island (Maritime Antarctica) waters and pyroclastic gravel impacted by volcanic mercury.

Deception Island is an active volcano in the Antarctica being volcanism a source of mercury. To improve the understanding of the Hg cycle in this remote ecosystem, pyroclastic gravel and water samples were collected and total (THg) and monomethylmercury (MMHg) concentrations were measured as well as the potential for Hg methylation. Gravel samples collected close to active fumaroles showed the highest THg levels (72 ng/g) while in water samples the highest concentrations of THg (1.2 ng/L) and MMHg (0.45 ng/L) where found. Methylation activity was barely observable in gravel samples. Biotic methylation rates in water were up to 13 times higher compared to those recorded previously in other polar waters. Abiotic methylation processes also play an important role, with up to 0.54 ± 0.43% of added Hg converted instantaneously to MMHg. These results suggest that Deception Island presents favourable conditions for MMHg explaining the elevated concentrations of both THg and MMHg in this ecosystem.

Mercury in sediments and vegetation in a moderately contaminated salt marsh (Tagus Estuary, Portugal).

Depth variations of total mercury (Hg) and methylmercury (MeHg) concentrations were studied in cores from non-colonized sediments, sediments colonized by Halimione portulacoides, Sarcocorniafruticosa and Spartina maritima and belowground biomass, in a moderately contaminated salt marsh (Tagus Estuary, Portugal). Concentrations in belowground biomass exceeded up to 3 (Hg) and 15 (MeHg) times the levels in sediments, and up to 198 (Hg) and 308 (MeHg) times those found in aboveground parts. Methylmercury in colonized sediments reached 3% of the total Hg, 50 times above the maximum values found in non-colonized sediments. The absence of correlations between total Hg concentrations in sediments and the corresponding MeHg levels suggested that methylation was only dependent on the environmental and microbiological factors. The analysis of belowground biomass at high-depth resolution (2 cm) provided evidence that Hg and MeHg were actively absorbed from sediments, with higher enrichment factors at layers where higher microbial activity was probably occurring. The results obtained in this study indicated that the biotransformation of Hg to the toxic MeHg could increase the toxicity of plant-colonized sediments.

Llaima volcano dataset: In-depth comparison of deep artificial neural network architectures on seismic events classification.

This data manuscript presents a set of signals collected from the Llaima volcano located at the western edge of the Andes in Araucania Region, Chile. The signals were recorded from the LAV station between 2010 and 2016. After individually processing and analyzing every signal, specialists from the Observatorio Vulcanológico de los Andes Sur (OVDAS) classified them into four class according to their event source: i) Volcano-Tectonic (VT); ii) Long Period (LP); iii) Tremor (TR), and iv) Tectonic (TC). The dataset is composed of 3592 signals separated by class and filtered to select the segment that contains the most representative part of the seismic event. This dataset is important to support researchers interested in studying seismic signals from active volcanoes and developing new methods to model time-dependent data. In this sense, we have published the manuscript "In-Depth Comparison of Deep Artificial Neural Network Architectures on Seismic Events Classification" [1] analyzing such signals with different Deep Neural Networks (DNN). The main contribution of such manuscript is a new DNN architecture called SeismicNet, which provided classification results among the best in the literature without demanding explicit signal pre-processing steps. Therefore, the reader is referred to such manuscript for the interpretation of the data.

Diversity of Bacterial Biosynthetic Genes in Maritime Antarctica.

Bacterial natural products (NPs) are still a major source of new drug leads. Polyketides (PKs) and non-ribosomal peptides (NRP) are two pharmaceutically important families of NPs and recent studies have revealed Antarctica to harbor endemic polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) genes, likely to be involved in the production of novel metabolites. Despite this, the diversity of secondary metabolites genes in Antarctica is still poorly explored. In this study, a computational bioprospection approach was employed to study the diversity and identity of PKS and NRPS genes to one of the most biodiverse areas in maritime Antarctica-Maxwell Bay. Amplicon sequencing of soil samples targeting ketosynthase (KS) and adenylation (AD) domains of PKS and NRPS genes, respectively, revealed abundant and unexplored chemical diversity in this peninsula. About 20% of AD domain sequences were only distantly related to characterized biosynthetic genes. Several PKS and NRPS genes were found to be closely associated to recently described metabolites including those from uncultured and candidate phyla. The combination of new approaches in computational biology and new culture-dependent and -independent strategies is thus critical for the recovery of the potential novel chemistry encoded in Antarctica microorganisms.

Mercury mobility and effects in the salt-marsh plant Halimione portulacoides: Uptake, transport, and toxicity and tolerance mechanisms.

The plant Halimione portulacoides, an abundant species widely distributed in temperate salt-marshes, has been previously assessed as bioindicator and biomonitor of mercury contamination in these ecosystems. The present study aims to assess uptake and distribution of total mercury (THg) and methylmercury (MMHg) within H. portulacoides, potential mercury release by volatilization through leaves, and toxicity and tolerance mechanisms by investigating plant photochemical responses. Stem cuttings of H. portulacoides were collected from a salt-marsh within the Tagus estuary natural protected area, and grown under hydroponic conditions. After root development, plants were exposed to 199HgCl2 and CH3201HgCl, and sampled at specific times (0, 1, 2, 4, 24, 72, 120, 168 (7 days) and 432 h (18 days)). After exposure, roots, stems and leaves were analysed for total 199Hg (T199Hg) and MM201Hg content. Photobiology parameters, namely efficiency and photoprotection capacity, were measured in leaves. Both THg and MMHg were incorporated into the plant root system, stems and leaves, with roots showing much higher levels of both isotope enriched spikes than the other plant tissues. Presence of both mercury isotopes in the stems and leaves and high significant correlations found between roots and stems, and stems and leaves, for both THg and MMHg concentrations, indicate Hg translocation between the roots and above-ground organs. Long-term uptake in stems and leaves, leading to higher Hg content, was more influenced by temperature and radiation than short-term uptake. However, the relatively low levels of both THg and MMHg in the aerial parts of the plant, which were influenced by temperature and radiation, support the possibility of mercury release by stems and leaves, probably via stomata aperture, as a way to eliminate toxic mercury. Regarding photochemical responses, few differences between control and exposed plants were observed, indicating high tolerance of this salt marsh plant to THg and MMHg.

A multidimensional concept for mercury neuronal and sensory toxicity in fish - From toxicokinetics and biochemistry to morphometry and behavior.

BACKGROUND: Neuronal and sensory toxicity of mercury (Hg) compounds has been largely investigated in humans/mammals with a focus on public health, while research in fish is less prolific and dispersed by different species. Well-established premises for mammals have been governing fish research, but some contradictory findings suggest that knowledge translation between these animal groups needs prudence [e.g. the relative higher neurotoxicity of methylmercury (MeHg) vs. inorganic Hg (iHg)]. Biochemical/physiological differences between the groups (e.g. higher brain regeneration in fish) may determine distinct patterns. This review undertakes the challenge of identifying sensitive cellular targets, Hg-driven biochemical/physiological vulnerabilities in fish, while discriminating specificities for Hg forms. SCOPE OF REVIEW: A functional neuroanatomical perspective was conceived, comprising: (i) Hg occurrence in the aquatic environment; (ii) toxicokinetics on central nervous system (CNS)/sensory organs; (iii) effects on neurotransmission; (iv) biochemical/physiological effects on CNS/sensory organs; (v) morpho-structural changes on CNS/sensory organs; (vi) behavioral effects. The literature was also analyzed to generate a multidimensional conceptualization translated into a Rubik's Cube where key factors/processes were proposed. MAJOR CONCLUSIONS: Hg neurosensory toxicity was unequivocally demonstrated. Some correspondence with toxicity mechanisms described for mammals (mainly at biochemical level) was identified. Although the research has been dispersed by numerous fish species, 29 key factors/processes were pinpointed. GENERAL SIGNIFICANCE: Future trends were identified and translated into 25 factors/processes to be addressed. Unveiling the neurosensory toxicity of Hg in fish has a major motivation of protecting ichtyopopulations and ecosystems, but can also provide fundamental knowledge to the field of human neurodevelopment.