A protocol for identifying suitable biomarkers to assess fish health: A systematic review

Effects of a glyphosate-based herbicide on the development and biochemical biomarkers of the freshwater copepod Notodiaptomus carteri (Lowndes, 1934)

In this work we analyzed the effects of Sulfosato Touchdown®, a glyphosate-based herbicide, on the ontogenic development and biochemical markers of the freshwater copepod Notodiaptomus carteri. A 30-days life-cycle experiment was carried out with three different glyphosate concentrations (0, 0.38, and 0.81 mg L-1) to analyze the developmental time from nauplii to adult copepods and their individual growth. An additional 10-days experiment with the same glyphosate concentrations was designed to evaluate the energy reserves (glycogen, proteins and lipids) and the activity of three antioxidant enzymes, superoxide dismutase (SOD), catalase, and glutathione-S-transferase (GST) in adult copepods, separately for females and males. We found that the lowest glyphosate concentration increased the nauplii and total development time. The highest glyphosate concentration prevented copepods from reaching the adult stage, inhibited the growth of the first copepodite stage and increased the GST and SOD activity in adult females. According to our results, the presence of this herbicide in freshwater systems could impose a risk in the ecological role of copepods in nature. This study will contribute to propose the Notodiaptomus genus as model specie for monitoring purposes in the Neotropical aquatic systems.

Feathers of Three Waterfowl Bird Species from Northern Iran for Heavy Metals Biomonitoring

Waterbirds are considered the effective sentinels of aquatic ecosystems contamination and their feathers are widely used as non-destructive biological tools for contaminant biomonitoring. In this work, we measure and evaluate the concentrations of lead, copper and zinc in the breast feathers of three species namely Fulica atra, Anas crecca and Anas platyrhynchos in the wetland National Park Boujagh. Levels of lead (Pb), copper (Cu) and zinc (Zn) were below the threshold that causes sub-lethal and reproductive effects. Significant differences in metal concentrations were found among bird species. The finding indicated that highest Pb and Zn concentrations were observed in common Coot. The effect of sex on heavy metal was observed for Pb in Anas platyrhynchos and while Cu, Zn in Anas crecca. Concentrations of metals were significantly (p < 0.05) higher in resident birds than in migratory. High levels of these heavy metals show that these birds can be used to monitor contamination in the wetland.

Banded tetra (Astyanax aeneus) as bioindicator of trace metals in aquatic ecosystems of the Yucatan Peninsula, Mexico: Experimental biomarkers validation and wild populations biomonitoring

Bioindicator organisms are important tools in environmental monitoring studies. Understanding this, the overall goal of the present study was to evaluate the sensitivity and viability of the native fish species Banded tetra, (Astyanax aeneus; Günther, 1860), widely spread in the aquatic ecosystems of the Yucatan Peninsula in Mexico, as a bioindicator organism. In order to do this, we performed a bioassay at sublethal concentrations using copper (CuSO₄) to experimentally evaluate and validate the relationship between the trace metals and oxidative stress biomarkers response [(catalase (CAT), lipoperoxidation content (LPO)], detoxification [(glutathione S-transferase (GST), metallothionein content (MT)] and neurotoxicity (AChE) in muscle of A. aeneus. Results showed changes in biomarkers after 96 h: Catalase activity (CAT) was significantly higher above 1.5 and 2 mg/L (154.35 and 172.50% increase, respectively); lipid peroxidation contents (TBARS), GST activity, and MT content were very similar to CAT activity at 1.5 and 2 mg/L of Cu. In terms of neurotoxicity, AChE activity was significantly inhibited at 0.1 mg/L (64%; p < 0.001) and 0.5 mg/L (44%; p < 0.001) of Cu. Based on the bioassay results, we performed a trace metal monitoring campaign in muscle of A. aeneus caught in 15 sites with different anthropogenic activities, during the summer of 2017, to establish a baseline of trace metals pollution in the state of Campeche. A. aeneus showed the highest trace metal accumulation in the following order: Al > Fe > Mn > Zn > Cu > Hg > Cr > Pb > Cd > V > As, while sites were arrange as follows: Xnoha lagoon > Palizada River > Candelaria River > Ululmal > Maravillas > López Mateos. PCA showed a cluster between biomarkers (GST, CAT, TBARS, and MT) and concentration of metals (Cd, Cu, Fe, Zn, Hg and Cr). Conversely, AChE inhibition was not related to a specific metal, but highest inhibitions (>50%) were present in those sites with intensive agricultural practices. These results determined that, based on its physiological response and trace metal bioaccumulation, Astyanax aeneus can be considered a good bioindicator for evaluating the presence of trace metals in tropical aquatic systems of the Yucatan Peninsula.

Evaluation of Toxicity on Ctenopharyngodon idella Due to Tannery Effluent Remediated by Constructed Wetland Technology

Aquatic pollution caused by industrial effluents is an environmental issue, imposing deleterious impacts on the overall environment, specifically, on humans, by disrupting the balance of the ecosystem. Among all the industries, tanneries are considered some of the most polluting due to heavy use of toxic organic and inorganic compounds during leather processing, most of which find their way into rivers, lakes, and streams, thus exerting adverse effects on aquatic life, particularly on fish. Considering the huge concentrations of pollutants present in tannery effluents, toxicity evaluation is of prime importance. Therefore, bioassays are usually employed to assess the acute toxicity of industrial effluents and efficiency of effluent clean-up technologies as they provide a thorough response of test species to the substances present in the tested media. In the present study, the toxic effects of tannery effluent on common grass carp (Ctenopharyngodon idella) were studied for 96 h in laboratory conditions. The effluent was added at different concentrations, before and after treatment by constructed wetlands (CWs). During this period, mortality data was collected to calculate the 96 h-LC50 (lethal concentration inducing 50% mortality) and acute toxicity of C. idella. In addition to this, observations on change in morphological, physiological, and behavioural patterns were also made every 24 h. The present toxicity assay revealed that the raw tannery effluent changed the morphology, physiology, and behavioural response of fish. Moreover, fish exposure to raw/untreated effluent caused high acute toxicity and 100% mortality, due to the presence of high concentrations of salts and chromium (Cr) metal. While treatment of tannery effluent by CWs vegetated with different plants (B. mutica, L. fusca, and T. domingensis) significantly reduced its toxicity and fish mortality as well, and inoculation of salt and Cr-tolerant endophytic bacteria (Enterobacter sp. HU38, Microbacterium arborescens HU33, and Pantoea stewartii ASI11) further reduced (up to 90%) its toxicity level. Hence, the use of CWs for tannery effluent treatment can be recommended to favour public health and promote the overall safety of the environment.

Depressed, hypertense and sore: Long-term effects of fluoxetine, propranolol and diclofenac exposure in a top predator fish

Pharmaceutical compounds are continuously released into the aquatic environment, resulting in their ubiquitous presence in many estuarine and coastal systems. As pharmaceuticals are designed to produce effects at very low concentrations and target specific evolutionary conserved pathways, there are growing concerns over their potential deleterious effects to the environment and specifically to aquatic organisms, namely in early life-stages. In this context, the long-term effects of exposure of juvenile meagre Argyrosomus regius to three different pharmaceuticals were investigated. Fish were exposed to environmental concentrations of one of three major used pharmaceuticals: the antidepressant fluoxetine (0.3 and 3 μg/L for 15 days), the anti-hypertensive propranolol and the non-steroidal anti-inflammatory agent diclofenac (0.3 and 15 μg/L for 30 days). Pharmaceuticals bioconcentration in fish muscle was examined, along with biomarkers in different tissues related with antioxidant and biotransformation responses (catalase, superoxide dismutase, ethoxyresorufin-O-deethylase and glutathione S-transferase), energetic metabolism (lactate dehydrogenase, isocitrate dehydrogenase and electron transport system activities), neurotransmission (acetylcholinesterase activity) and oxidative damage (DNA damage and lipid peroxidation levels). Overall, each pharmaceutical had different potential for bioconcentration in the muscle (FLX > PROP > DCF) and induced different biological responses: fluoxetine was the most toxic compound to juvenile meagre, affecting fish growth, triggering antioxidant defense responses, inhibiting detoxification mechanisms and increasing lipid peroxidation and DNA damage in the liver; propranolol exposure increased DNA damage and decreased aerobic metabolism in fish muscle; and diclofenac showed no potential to bioconcentrate, yet it affected fish metabolism by increasing cellular energy consumption in the muscle and consequently reducing fish net energy budget. The diverse response patterns evidence the need for future research focused on pharmaceuticals with different modes of action and their exposure effects on organismal physiological mechanisms and homeostatic status. Ultimately, the combination of sub-individual and individual responses is key for ecologically relevant assessments of pharmaceutical toxicity.

Metalloproteomic approach of mercury-binding proteins in liver and kidney tissues of Plagioscion squamosissimus (corvina) and Colossoma macropomum (tambaqui) from Amazon region: Possible identification of mercury contamination biomarkers

Fish is an important source of protein, vitamins, and minerals. However, this food is also a major source of human exposure to toxic contaminants such as mercury. Thus, this paper aimed to evaluate mercury-binding proteins for possible application as biomarkers of mercury contamination in hepatic and renal tissues of Plagioscion squamosissimus (carnivorous fish) and Colossoma macropomum (omnivorous fish) from the Amazon region using metalloproteomic approach. The proteome of hepatic and renal tissues of fish species was separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), and the mercury concentrations in protein spots were determined by graphite furnace atomic absorption spectrometry (GFAAS). Finally, the protein spots associated to mercury were characterized by electrospray ionization mass spectrometry (ESI-MS/MS). The activity of antioxidant enzymes (SOD, CAT, GPx, and GST) and lipid peroxidation (LPO) were also determined. The results showed that the highest concentrations of mercury were found in the carnivorous species (P. squamosissimus) and that the accumulation pattern of this metal was higher in hepatic tissues than in renal tissues for both species. A tendency was observed for greater enzymatic activity in the hepatic and renal tissues of P. squamosissimus, the species with the highest concentration of mercury. Only GPx activity in the kidney and GST in the liver were lower for the P. squamosissimus species, and this finding can be explained by the interaction of mercury with these enzymes. The data obtained by ESI-MS/MS allowed for the characterization of the protein spots associated to mercury, revealing proteins involved in energy metabolism, biomolecules transport, protein synthesis and degradation, cell differentiation, gene regulation, and the antioxidant system. The results obtained in the present study can contribute to understanding the physiological processes underlying mercury toxicity and have provided new perspectives on possible candidates for mercury contamination biomarkers in fish.

Uso de biomarcadores en la evaluación ambiental de ecosistemas marinos en América

The use of biomarkers in the assessment of the marine environmental status offers an integrated approach to the effects caused by diverse pollutants. This article compiles and analyzes the original research on the study of possible biomarkers in wild coastal-marine organisms from America. One of the outcomes of this review research is the need for a continuous evaluation of organisms in conjunction with the assessment of environmental vari-ables and the levels of pollutants that may be found in any ecosystem. It is well stated that the use of biomarkers is a practical tool for the environmental management; however, some limitations apply and there are several questions in regards to specificity, sensibility, usability, replicability, and interpretation to be solved, yet. Along the American continent, multiple biomarkers have been used to evaluate specific pollutants or highly impacted zones at marine-coastal environments. The most commonly used organisms are fishes and bivalves and they have been also extensively used in marine turtles. In regards of the type of biomarkers, plenty of authors integrate biomarkers from different groups, sorted in this review as biometric biomarkers (morphologic and corporal in-dexes), histological biomarkers (for tissues), molecular biomarkers (genetic) and biochemical and physiological biomarkers (both at the cellular and molecular levels). Following this classification, the most used biomarkers were biochemical and physiological biomarkers, due to the great advantages and information that they provide. It is of utmost importance to set guidelines and referenced threshold values for each biomarker to allow the early environmental diagnosis and integrated evaluation of harmful pollutants effects. Keywords: Biomarkers, environmental assessment, America.

Assessing endocrine disruption in freshwater fish species from a "hotspot" for estrogenic activity in sediment

Little is known about sediment-bound exposure of fish to endocrine disrupting chemicals (EDC) under field conditions. This study aimed to investigate potential routes of EDC exposure to fish and whether sediment-bound contaminants contribute towards exposure in fish. Tench (Tinca tinca) and roach (Rutilus rutilus) as a benthic and pelagic living fish species, respectively, were sampled at the Luppe River, previously described as a "hotspot" for accumulation of EDC in sediment. A field reference site, the Laucha River, additionally to fish from a commercial fish farm as reference were studied. Blackworms, Lumbriculus variegatus, which are a source of prey for fish, were exposed to sediment of the Luppe River and estrogenic activity of worm tissue was investigated using in vitro bioassays. A 153-fold greater estrogenic activity was measured using in vitro bioassays in sediment of the Luppe River compared the Laucha River. Nonylphenol (NP; 22 mg/kg) was previously identified as one of the main drivers of estrogenic activity in Luppe sediment. Estrogenic activity of Luppe exposed worm tissue (14 ng 17β-estradiol equivalents/mg) indicated that food might act as secondary source to EDCs. While there were no differences in concentrations of NP in plasma of tench from the Luppe and Laucha, vitellogenin, a biomarker for exposure to EDCs, was induced in male tench and roach from the Luppe River compared to both the Laucha and cultured fish by a factor of 264 and 90, respectively. However, no histological alterations in testis of these fish were observed. Our findings suggest that sediments substantially contribute to the overall EDC exposure of both benthic and pelagic fish but that the exposure did not impact gonad status of the fish.

Difference in biochemical markers in the gibel carp (Carassius auratus gibelio) upstream and downstream of the hydropower plant

However the physiological stress in aquatic organisms associated with hydropower plants (HPP) ecosystems has been previously investigated, no studies have so far assessed it on biochemical level. Therefore this study evaluated an oxidative stress and toxicity in the gibel carp Carassius auratus gibelio associated with a small-scale HPP in the West Ukraine. A battery of liver, brain and blood markers was evaluated individuals inhabiting upstream and downstream of the dam of the small-scale Kasperivtci HPP (KHPP; an installed capacity of 7.5 MW), and from a reference site. Number of alterations were noted in fish from the KHPP impoundment facility including signs of oxidative stress (a decrease in superoxide dismutase (SOD) activity and an increase in protein carbonyls) and cytotoxicity (an increase in micronucleated erythrocytes and caspase-3 activity). No changes in DNA fragmentation in hepatocytes or brain cholinesterase activity were detected. As demonstrated by the integral stress index, fish associated with downstream of the dam revealed the greatest alterations reflected by the combined oppression of antioxidant system (SOD, catalase) and pro-oxidants (thiobarbituric acid reactive substances and oxyradicals), low concentration of metallothioneins, but high cathepsin D activity (as markers of lysosomal dysfunction and autophagy) and increased vitellogenin concentration in males (indicating an endocrine disruption). The study highlights that fish inhabiting ecosystems associated with HPP, particularly downstream of the dam, may face additional stresses with long-term effects yet to be evaluated.

Effects of environmental pollution on the rDNAomics of Amazonian fish

Pollution is a growing environmental problem throughout the world, and the impact of human activities on biodiversity and the genetic variability of natural populations is increasingly preoccupying, given that adaptive processes depend on this variability, in particular that found in the repetitive DNA. In the present study, the mitochondrial DNA (COI) and the distribution of repetitive DNA sequences (18S and 5S rDNA) in the fish genome were analysed in fish populations inhabiting both polluted and unpolluted waters in the northern Amazon basin. The results indicate highly complex ribosomal sequences in the fish genome from the polluted environment because these sequences are involved primarily in the maintenance of genome integrity, mediated by a systematic increase in the number of copies of the ribosomal DNA in response to changes in environmental conditions.

Insights into the Potential of the Atlantic Cod Gut Microbiome as Biomarker of Oil Contamination in the Marine Environment

BACKGROUND

Microorganisms are widespread in all environments, including in and on animal bodies. The gut microbiome has an essential influence on fish health, and is affected by several persistent and harmful organic and inorganic contaminants. Considering the shifts in gut microbiota composition observed in those studies, we hypothesized that certain microbial groups in the gut can serve as indicators of pollution. To test this hypothesis, we explored the possibility of identifying key microbial players that indicate environmental contamination.

METHODS

Published 16S rRNA gene amplicon sequencing data generated from the gut microbiota of Atlantic cod caught in geographically different Norwegian waters were used for bacterial diversity comparison.

RESULTS

Different microbiomes were identified between the northern Norway and southern Norway samples. Several bacterial genera previously identified as polycyclic aromatic hydrocarbon degraders were present only in the samples collected in the southern Norway area, suggesting fish contamination with oil-related compounds.

CONCLUSIONS

The results contribute to the identification of bacterial taxa present in the Atlantic cod gut that indicate fish exposure to contaminants in the marine environment.

An automated computer vision based preliminary study for the identification of a heavy metal (Hg) exposed fish-channa punctatus

Fishes available in the market may be cultured either in fresh or contaminated water bodies. Heavy metals are one of those contaminants which may cause menace to fish health and thereby affect the health of living beings consuming them. The identification of heavy metal residues in fish samples is a challenging task and may require expensive and sophisticated instruments and testing. This paper investigates visual changes which may be used as benchmark for differentiating between fresh water and heavy metal exposed fishes. The proposed method is an automated non-destructive image processing method for identifying visual changes which can be used to differentiate between controlled (untreated) and heavy metals exposed (treated) fishes. The eye of the fish from digital images is considered as focal tissue that was automatically segmented using the Circular Hough Transform and adaptive intensity thresholding. Post segmentation, a potential feature is identified and transformed into mathematical parameters for classification of a fish sample as fresh or heavy metal exposed water fish. The proposed method can identify and translate the potential visual feature for ease of understanding. The accuracy of the proposed method is high, and computation time elapsed indicates the possibility of using such algorithm for real time detection in related field.

Selenium cytotoxicity in Tetrahymena thermophila: New clues about its biological effects and cellular resistance mechanisms

Selenium is an essential micronutrient but at high concentrations can produce severe cytotoxicity and genomic damage. We have evaluated the cytotoxicity, ultrastructural and mitochondrial alterations of the two main selenium inorganic species; selenite and selenate, in the eukaryotic microorganism Tetrahymena thermophila. In this ciliate, selenite is more toxic than selenate. Their LC₅₀ values were calculated as 27.65 μM for Se(IV) and 56.88 mM for Se(VI). Significant levels of peroxides/hydroperoxides are induced under low-moderate selenite or selenate concentrations. Se(VI) exposures induce an immediate mitochondrial membrane depolarization. Selenium treated cells show an intense vacuolization and some of them present numerous discrete and small electrondense particles, probably selenium deposits. Mitochondrial fusion, an intense swelling in peripheral mitochondria and mitophagy are detected in selenium treated cells, especially in those exposed to Se (IV). qRT-PCR analysis of diverse genes, encoding relevant antioxidant enzymes or other proteins, like metallothioneins, involved in an environmental general stress response, have shown that they may be crucial against Se(IV) and/or Se (VI) cytotoxicity.

Waterborne manganese modulates immunity, biochemical, and antioxidant parameters in the blood of red seabream and black rockfish

Immunotoxic effects of manganese (Mn) were investigated in the blood of the economically important marine fish, red seabream (Pagrus major) and black rockfish (Sebastes schlegelii) when exposed to different concentrations of Mn (0, 0.5, 1, and 2 mg L^-1) for 14 days. During exposure, the levels of alternative complement activity in both fish were significantly lowered at 2 mg L^-1 of Mn of exposure. Lysozyme activity was significantly decreased in black rockfish in all concentrations of Mn after 14 days, while in red seabream, the decrease was significant with concentrations of 1 and 2 mg L^-1 of Mn after 7 and 14 days of exposure. A significantly low level was observed only in the 2 mg L^-1-exposed red seabream on day 14 of exposure. The concentrations of hemoglobin, red blood cells, white blood cells, and total serum proteins were significantly decreased in both fish under exposure to 1 and 2 mg L^-1 of Mn, while cortisol, alanine transferase, aspartate transaminase, and alkaline phosphatase levels were significantly increased compared to the levels of control groups. No significant change was found in serum glucose and albumin except in red seabream exposed to 2 mg L^-1 of Mn for 14 days. The responses of the antioxidant defense system were significantly induced in both fish after exposure to 1 and 2 mg L^-1 of Mn on day 7 and 14 of exposure. Taken together, alterations of these parameters suggest the immunotoxicity of waterborne Mn produced by the modulation of hematological components and the induction of oxidative stress in the blood of these marine fish.

Significance of the goby Zosterisessor ophiocephalus as a sentinel species for Venice Lagoon contamination: Combining biomarker responses and bioaccumulation

The Venice Lagoon is an interesting example of an ecosystem suffering for a considerable anthropogenic impact, resulting in high concentrations of persistent organic pollutants (POPs) in lagoon sediments and seafood. In this context, biomonitoring is a crucially important task. The present study aimed at evaluating the validity of a multiple biomarker approach in a benthic fish species. A total of 567 Zosterisessor ophiocephalus (Gobiidae) fish were collected in spring and autumn from three areas of Venice Lagoon (Porto Marghera, Val di Brenta, and Cà Roman) showing high, intermediate and low amounts of POPs, respectively. Aryl hydrocarbon receptor (AHR) and cytochrome P450 1A (CYP1A) mRNA levels, CYP1A protein amount and ethoxyresorufin O-deethylase activity (EROD) were measured in pooled liver and gills (mRNA levels only). Such biological data were then compared with polychlorinated biphenyls (PCBs) residues, measured in grass goby muscle by gas chromatography. Aryl hydrocarbon receptor and CYP1A mRNAs, protein and EROD were upregulated in accordance with PCB amounts measured in Z. ophiocephalus muscles. In fact, the highest AHR and CYP1A induction was observed in fish sampled in close proximity of the industrial area of Porto Marghera. Overall, the present study confirm the grass goby as a reliable sentinel species for Venice Lagoon, and AHR/CYP1A/EROD as a sensitive set of biomarkers of exposure for AHR ligands.

Integrated assessment of sediment contaminant levels and biological responses in sentinel fish species Atherinella brasiliensis from a sub-tropical estuary in south Atlantic

This study combined data of the concentrations of metals, polycyclic aromatic hydrocarbons (PAHs) and pharmaceuticals and personal hygiene products (PPCPs) in the sediments and the biological responses of the Atherinella brasiliensis fish in two different sites and climate seasons in the Estuarine-Lagoon Complex of Iguape-Cananéia, Southeast Brazil. The presence of metals, PAHs, and PPCPs were observed in the sediments demonstrating the contamination throughout the system with contributions of sewage and residues disposal, oil and combustion of biomass and fossil fuels. Higher contaminations were identified in the point of greater human presence (C - Cananéia City), especially during the cold-dry season. The influence of anthropic activities and variations in the estuarine conditions, such as lower hydrodynamics during the lower rainfall period, were observed. In fish, spatial and seasonal changes in the parameters of oxidative stress and biotransformation, genotoxicity and histopathological alterations followed the same trend, with more pronounced responses in C in the cold-dry season. The biological responses of the fish revealed adverse effects in the local species population and indicated the presence of metals, PAHs and PPCPs as stressors. The multivariate analysis and the integrated biomarker response index (IBR) corroborated with these results, also indicating that site C had the worst environmental quality. The present study provides new information about the contamination of the sediments of Estuarine-Lagoon Complex of Iguape-Cananéia and the chronic exposure to contaminants in A. brasiliensis. Therefore, contributing to a better understanding of the local environmental quality with data that can support protective management of the area.

Complex effects of pollution on fish in major rivers in the Czech Republic

Monitoring the contamination level in aquatic environments and assessing the impact on aquatic life occurs throughout the world. In the present study, an approach based on a combination of biomarkers and the distribution of various industrial and municipal pollutants was used to investigate the effect of aquatic environmental contamination on fish. Monitoring was performed in ten rivers in the Czech Republic (Berounka, Dyje, Elbe, Lužnice, Odra, Ohře, Otava, Sázava, Svratka, and Vltava rivers, with one or two locations in each river) at the same sites that were regularly monitored within the Czech National Monitoring Program in 2007-2011. Health status, hepatic ethoxyresorufin-O-deethylase (EROD) activity, total cytochrome P450 content, and the plasma vitellogenin concentration were assessed in wild chub (Squalius cephalus) males caught at the monitored sites. The contamination level was the highest in the Svratka River downstream of Brno. Among all measured persistent organic pollutants (POPs), polychlorinated biphenyls and dichlorodiphenyltrichloroethane and its metabolites were the major contributors of POPs in fish muscle. Elbe, Odra, and Svratka rivers were identified as the most polluted. Fish from these locations showed reduced gonad size, increased vitellogenin concentration in male plasma, EROD, and total cytochrome P450 content. These biomarkers can be used for future environmental monitoring assessments. Overall, this study improves our understanding of the relationship between human activities and pollutant loads and further contributes to the decision to support local watershed managers to protect water quality in this region.

Classification of marine microdebris: A review and case study on fish from the Great Barrier Reef, Australia

Marine debris, and in particular plastic pollution, is ubiquitous throughout global marine environments. Here, we present a classification of marine microdebris (i.e. debris between 0.1 μm and <5 mm) tailored to represent synthetic, semi-synthetic and naturally-derived items. The specific aim of this classification is to introduce a level of consistency in the higher-level characterisation of marine microdebris, thereby improving the overall reporting on marine microdebris contamination. We first conducted an extensive literature review on the accumulation of ingested debris in fish to identify discrepancies in marine microdebris reporting as a basis for the new classification. The review reveals the diverse nature of ingested marine microdebris, including items that are non-plastic but often incorrectly reported on as microplastics. We then applied our classification to a case study on wild-caught juvenile coral trout, Plectropomus spp., from the Great Barrier Reef World Heritage Area, Australia. This first report on accumulation of ingested marine debris in commercial fish on the reef demonstrates a high frequency of occurrence and a prevalence of semi-synthetic and naturally-derived fibres. Based on our findings, we offer recommendations on potential improvements for the classification presented, ultimately contributing to a more realistic assessment of the ecological risks of marine microdebris.

De Novo Hepatic Transcriptome Assembly and Systems Level Analysis of Three Species of Dietary Fish, Sardinops sagax, Scomber japonicus, and Pleuronichthys verticalis

The monitoring of marine species as sentinels for ecosystem health has long been a valuable tool worldwide, providing insight into how both anthropogenic pollution and naturally occurring phenomena (i.e., harmful algal blooms) may lead to human and animal dietary concerns. The marine environments contain many contaminants of anthropogenic origin that have sufficient similarities to steroid and thyroid hormones, to potentially disrupt normal endocrine physiology in humans, fish, and other animals. An appropriate understanding of the effects of these endocrine disrupting chemicals (EDCs) on forage fish (e.g., sardine, anchovy, mackerel) can lead to significant insight into how these contaminants may affect local ecosystems in addition to their potential impacts on human health. With advancements in molecular tools (e.g., high-throughput sequencing, HTS), a genomics approach offers a robust toolkit to discover putative genetic biomarkers in fish exposed to these chemicals. However, the lack of available sequence information for non-model species has limited the development of these genomic toolkits. Using HTS and de novo assembly technology, the present study aimed to establish, for the first time for Sardinops sagax (Pacific sardine), Scomber japonicas (Pacific chub mackerel) and Pleuronichthys verticalis (hornyhead turbot), a de novo global transcriptome database of the liver, the primary organ involved in detoxification. The assembled transcriptomes provide a foundation for further downstream validation, comparative genomic analysis and biomarker development for future applications in ecotoxicogenomic studies, as well as environmental evaluation (e.g., climate change) and public health safety (e.g., dietary screening).

Responses of biomarkers in Atlantic salmon (Salmo salar) following exposure to environmentally relevant concentrations of complex metal mixture (Zn, Cu, Ni, Cr, Pb, Cd). Part II

The aim of this research was to assess interactions between metals at low exposure concentrations (Maximum-Permissible-Concentrations accepted for the inland waters in EU) and to assess possible influence of background exposure (10-times reduced concentration of a single metal) on toxicological significance of selected biomarkers in Salmo salar after treatment with metal mixture (Zn - 0.1, Cu - 0.01, Ni - 0.01, Cr - 0.01, Pb - 0.005 and Cd - 0.005 mg/L). The tissue-specific bioaccumulation, genotoxicity and cytotoxicity responses (erythrocytic nuclear abnormalities assay) in peripheral blood, kidneys, gills and liver erythrocytes of fish to metal mixtures were assessed after 14 days treatment. Treatment with primary mixture (MIX) or two variants of this mixture (Cr↓ (10 times reduced Cr⁶⁺ concentration) and Cu↓ (10 times reduced Cu²⁺ concentration)) induced the strongest responses in genotoxicity and cytotoxicity endpoints. Exposure to these mixtures highly affected Zn, Cu and Cd bioaccumulation in liver tissue. The highest amount of Ni accumulated was measured after Cd↓ treatment in all tissues. Treatments with reduced concentration of non-essential metal resulted in an increased accumulation of Pb, Ni, or Cd; treatments with reduced concentration of essential metal resulted in a reduced accumulation of certain metals (especially Cd and Pb) in tissues compared between treatments. Glucose content in blood and behavioural endpoints were evaluated after short-term exposure to metal mixtures (MIX, Cr↓, Cu↓). Significant increase in blood glucose concentration was measured after all treatments. These metal mixtures elicit significant behavioural alterations in fish. Consequently, this research revealed a significant influence of background exposure considering mixture toxicity.

Development of an oxidative stress in vitro assay in zebrafish (Danio rerio) cell lines

The nuclear factor erythroid 2-related factor 2 (Nrf2) is a key regulator of cellular defense against oxidative stress and correlated with classical toxicological endpoints. In vitro methods using fish cell lines for the assessment of aquatic toxicity are needed for mechanistic studies and as an alternative to in vivo. We describe an in vitro assay to study oxidative stress using zebrafish cell lines. Transfection efficiency of twelve commercially available transfection reagents were tested in the zebrafish cell lines ZFL, ZF4, and Pac2. The most efficient reagent for each cell line was selected for further experiments. Cells were transiently transfected with an Nrf2-responsive luciferase plasmid. The assay was tested using the oxidative stress inducing chemicals tertbutylhydroquinone, hydrogen peroxide, and sulforaphane. Of the transfected cell lines, ZF4 and ZFL showed higher sensitivity. The latter were used to study potential oxidative stress induced by pesticides (diazinon, deltamethrin, atrazine, metazachlor, terbutylazine, diuron). Besides known inducers, Nrf2 activity was also significantly induced by diazinon, deltametrin, diuron, and metazachlor. Activation of Nrf2 by metazachlor is a novel finding. The described assay could be a valuable tool for research in toxicology to study the stress response of both pure chemicals and environmental water samples.