Thyroid-hormone-disrupting chemicals are increasingly attracting attention because of their potential harmful effects on animal health, including on fishes. Here, we investigated the effects of exposure to the thyroid-hormone-disrupting chemicals 6-propyl-2-thiouracil (PTU) and tetrabromobisphenol a (TBBPA) on swim bladder inflation, eye development, growth, swimming performance, and the expression of thyroid-related genes in Japanese medaka (Oryzias latipes). PTU exposure resulted in reductions in eye size, growth, and swim bladder inflation, and these effects led to poorer swimming performance. These phenotypic effects were accompanied by increased expression of the thyroid-stimulating hormone subunit beta (tshβ) paralog tshβ-like, but there were no significant changes in expression for tshβ, deiodinase 1 (dio1), deiodinase 2 (dio2), and thyroid hormone receptor alpha (trα) and beta (trβ). For PTU exposure, we identified the key event (swim bladder inflation reduction) and an adverse outcome (swimming performance reduction). No significant effects from TBBPA exposure were seen on swim bladder inflation, eye development, growth, or swimming performance. However, expression of tshβ-like and tshβ (significantly enhanced) and trα and trβ (significantly reduced) were affected by TBBPA exposure albeit not in dose-dependent manners. There were no effects of TBBPA on the expression of dio1 and dio2. We thus show that the two thyroid-hormone-disrupting chemicals PTU and TBBPA differ in their effect profiles with comparable effects on the studied phenotypes and thyroid-related gene expression to those reported in zebrafish.

INTRODUCTION: all decapod crustaceans are considered potentially susceptible to White Spot Syndrome Virus (WSSV) infection, but the degree of White Spot Disease (WSD) susceptibility varies widely between species. The European shore crab Carcinus maenas can be infected with the virus for long periods of time without signs of disease. Given the high mortality rate of susceptible species, the differential susceptibility of these resistant hosts offers an opportunity to investigate mechanisms of disease resistance. METHODS: Here, the temporal transcriptional responses (mRNA and miRNA) of C. maenas following WSSV injection were analysed and compared to a previously published dataset for the highly WSSV susceptible Penaeus vannamei to identify key genes, processes and pathways contributing to increased WSD resistance. RESULTS: We show that, in contrast to P. vannamei, the transcriptional response during the first 2 days following WSSV injection in C. maenas is limited. During the later time points (7 days onwards), two groups of crabs were identified, a recalcitrant group where no replication of the virus occurred, and a group where significant viral replication occurred, with the transcriptional profiles of the latter group resembling those of WSSV-susceptible species. We identify key differences in the molecular responses of these groups to WSSV injection. DISCUSSION: We propose that increased WSD resistance in C. maenas may result from impaired WSSV endocytosis due to the inhibition of internal vesicle budding by dynamin-1, and a delay in movement to the nucleus caused by the downregulation of cytoskeletal transcripts required for WSSV cytoskeleton docking, during early stages of the infection. This response allows resistant hosts greater time to fine-tune immune responses associated with miRNA expression, apoptosis and the melanisation cascade to defend against, and clear, invading WSSV. These findings suggest that the initial stages of infection are key to resistance to WSSV in the crab and highlight possible pathways that could be targeted in farmed crustacean to enhance resistance to WSD.

A wide range of health effects in fish have been reported for exposure to wastewater treatment work (WwTW) effluents including feminized responses in males. Most of these exposure studies, however, have assessed acute health effects and chronic exposure effects are less well established. Using an Estrogen Responsive Element-Green Fluorescent Protein (ERE-GFP)-Casper transgenic zebrafish, we investigated chronic health effects and life stage sensitivities for exposure to an estrogenic WwTW effluent and the synthetic estrogen 17α-ethinylestradiol (EE2). Exposure to the WwTW effluent (at full strength;100%) and to 10 ng/L (nominal) EE2 delayed testis maturation in male fish but accelerated ovary development in females. Exposure to 50% and 100% effluent, and to 10 ng/L EE2, also resulted in skewed sex ratios in favor of females. Differing patterns of green fluorescent protein (GFP) expression, in terms of target tissues and developmental life stages occurred in the ERE-GFP- zebrafish chronically exposed to 100% effluent and reflected the estrogenic content of the effluent. gfp and vitellogenin (vtg) mRNA induction were positively correlated with measured levels of steroidal estrogens in the effluent throughout the study. Our findings illustrate the importance of a fish’s developmental stage for estrogen exposure effects and demonstrate the utility of the ERE-GFP zebrafish for integrative health analysis for exposure to estrogenic chemical mixtures.

Silver is a non-essential, toxic metal widespread in freshwaters and capable of causing adverse effects to wildlife. Its toxic effects have been studied in detail but less is known about how sensitivity varies during development and whether pre-exposures affect tolerance upon re-exposure. We address these knowledge gaps using the zebrafish embryo (Danio rerio) model to investigate whether exposures encompassing stages of development prior to mid-blastula transition, when chorion hardening and epigenetic reprogramming occur, result in greater toxicity compared to those initiated after this period. We conducted exposures to silver initiated at 0.5 h post fertilisation (hpf) and 4 hpf to determine if toxicity differed. In parallel, we exposed embryos to the methylation inhibitor 5-azacytidine as a positive control. Toxicity increased when exposures started from 0.5 hpf compared to 4 hpf and LC50 were significantly lower by 1.2 and 7.6 times for silver and 5-azacyitidine, respectively. We then investigated whether pre-exposure to silver during early development (from 0.5 or 4 hpf) affected the outcome of subsequent exposures during the larvae stage, and found no alterations in toxicity compared to naïve larvae. Together, these data demonstrate that during early development zebrafish embryos are more sensitive to silver when experiments are initiated at the one-cell stage, but that pre-exposures do not influence the outcome of subsequent exposures, suggesting that no long-lasting memory capable of influencing future susceptibility was maintained under our experimental conditions. The finding that toxicity is greater for exposures initiated at the one-cell stage has implications for designing testing systems to assess chemical toxicity.

We characterized the ontogeny and dynamics of gonadal development, embryogenesis, and gestation in captive stocks of the viviparous redtail splitfin,<i> Xenotoca eiseni</i>. Using histology, we showed that gonads were fully differentiated at the time of birth with a male:female sex ratio of 1:1 in the captive stock. External secondary sex features included a modified anal fin and a distinctive orange tail coloration. These features first appeared at 4 weeks after birth and were discriminative for males thereafter. There was no sex-related dichotomy in body size, and <i>X. eiseni</i> reached sexual maturity at approximately 12 weeks of age. We found no evidence for sperm storage in females. Gestation normally took 6 weeks, and there was a positive correlation between female body size and the number of offspring produced, with up to 27 offspring for a single pregnancy. Yolk is the main food source for developing embryos for the period up to 2 weeks, and thereafter, trophotaeniae in embryos act as nutrient exchange surfaces in the ovarian lumen, which subsequently undergo complete regression within 2 weeks of birth. In our final analysis, we discuss the great potential of <i>X. eiseni</i> as a model for studying the effects of chemicals on sexual development.

Brominated flame retardants are known to disrupt thyroid hormone (TH) homeostasis in several vertebrate species, but the molecular mechanisms underlying this process and their effects on TH-sensitive tissues during the stages of early development are not well characterised. In this study, we exposed zebrafish (Danio rerio) embryo-larvae to 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) and tetrabromobisphenol a (TBBPA) via the water for 96 h from fertilisation and assessed for lethality, effects on development and on the expression of a suite of genes in the hypothalamic-pituitary-thyroid (HPT) axis via both real time quantitative PCR (qRT-PCR) on whole body extracts and whole mount in situ hybridisation (WISH) to identify tissue targets. The 96-h lethal median concentration (96h-LC50) for TBBPA was 0.9 μM and mortality was preceded by retardation of development (smaller animals) and morphological deformities including, oedemas in the pericardial region and tail, small heads, swollen yolk sac extension. Exposure to BDE-47 did not affect zebrafish embryo-larvae survival at any of the concentrations tested (1–100 μM) but caused yolk sac and craniofacial deformities, a curved spine and shorter tail at the highest exposure concentration. TBBPA exposure resulted in higher levels of mRNAs for genes encoding deiodinases (dio1), transport proteins (ttr), the thyroid follicle synthesis protein paired box 8 (pax8) and glucuronidation enzymes (ugt1ab) and lower levels of dio3b mRNAs in whole body extracts, with responses varying with developmental stage. BDE-47 exposure resulted in higher levels of thrb, dio1, dio2, pax8 and ugt1ab mRNAs and lower levels of ttr mRNAs in whole body extracts. TBBPA and BDE-47 therefore appear to disrupt the TH system at multiple levels, increasing TH conjugation and clearance, disrupting thyroid follicle development and altering TH transport. Compensatory responses in TH production/ metabolism by deiodinases were also evident. WISH analyses further revealed that both TBBPA and BDE-47 caused tissue-specific changes in thyroid receptor and deiodinase enzyme expression, with the brain, liver, pronephric ducts and craniofacial tissues appearing particularly responsive to altered TH signalling. Given the important role of TRs in mediating the actions of THs during key developmental processes and deiodinases in the control of peripheral TH levels, these transcriptional alterations may have implications for TH sensitive target genes involved in brain and skeletal development. These findings further highlight the potential vulnerability of the thyroid system to disruption by BFRs during early developmental windows.

Fish can be exposed to a variety of neuroactive pharmaceuticals via the effluent discharges from wastewater treatment plants and concerns have arisen regarding their potential impacts on fish behaviour and ecology. In this study, we investigated the uptake of 14 neuroactive pharmaceuticals from a treated wastewater effluent into blood plasma and brain regions of roach (Rutilus rutilus) after exposure for 15 days. We show that a complex mixture of pharmaceuticals including, 6 selective serotonin reuptake inhibitors, a serotonin-noradrenaline reuptake inhibitor, 3 atypical antipsychotics, 2 tricyclic antidepressants and a benzodiazepine, concentrate in different regions of the brain including the telencephalon, hypothalamus, optic tectum and hindbrain of effluent-exposed fish. Pharmaceuticals, with the exception of nordiazepam, were between 3–40 fold higher in brain compared with blood plasma, showing these neuroactive drugs are readily uptaken, into brain tissues in fish. To assess for the potential for any adverse ecotoxicological effects, the effect ratio was calculated from human therapeutic plasma concentrations (HtPCs) and the measured or predicted fish plasma concentrations of pharmaceuticals. After accounting for a safety factor of 1000, the effect ratios indicated that fluoxetine, norfluoxetine, sertraline, and amitriptyline warrant prioritisation for risk assessment studies. Furthermore, although plasma concentrations of all the pharmaceuticals were between 33 and 5714-fold below HtPCs, alterations in serotonin, glutamate, acetylcholine and tryptophan concentrations were observed in different brain regions of effluent-exposed fish. This study highlights the importance of determining the potential health effects arising from the concentration of complex environmental mixtures in risk assessment studies.

Estrogen plays fundamental roles in a range of developmental processes and exposure to estrogen mimicking chemicals has been associated with various adverse health effects in both wildlife and human populations. Estrogenic chemicals are found commonly as mixtures in the environment and can have additive effects, however risk analysis is typically conducted for single-chemicals with little, or no, consideration given for an animal's exposure history. Here we developed a transgenic zebrafish with a photoconvertable fluorophore (Kaede, green to red on UV light exposure) in a skin pigment-free mutant element (ERE)-Kaede-Casper model and applied it to quantify tissue-specific fluorescence biosensor responses for combinations of estrogen exposures during early life using fluorescence microscopy and image analysis. We identify windows of tissue-specific sensitivity to ethinylestradiol (EE2) for exposure during early-life (0-5 dpf) and illustrate that exposure to estrogen (EE2) during 0-48 hpf enhances responsiveness (sensitivity) to different environmental estrogens (EE2, genistein and bisphenol A) for subsequent exposures during development. Our findings illustrate the importance of an organism's stage of development and estrogen exposure history for assessments on, and possible health risks associated with, estrogen exposure.

Sex steroid hormones including estrogens and androgens play fundamental roles in regulating reproductive activities and they act through estrogen and androgen receptors (ESR and AR). These steroid receptors have evolved from a common ancestor in association with several gene duplications. In most vertebrates, this has resulted in two ESR subtypes (ESR1 and ESR2) and one AR, whereas in teleost fish there are at least three ESRs (ESR1, ESR2a and ESR2b) and two ARs (ARα and ARβ) due to a lineage-specific whole genome duplication. Functional distinctions have been suggested among these receptors, but to date their roles have only been characterized in a limited number of species. Sexual differentiation and the development of reproductive organs are indispensable for all animal species and in vertebrates these events depend on the action of sex steroid hormones. Here we review the recent progress in understanding of the functions of the ESRs and ARs in the development and expression of sexually dimorphic characteristics associated with steroid hormone signaling in vertebrates, with representative fish, amphibians, reptiles, birds and mammals.

In mammals, the pregnane X receptor (PXR) is a transcription factor with a key role in regulating expression of several genes involved in drug biotransformation. PXR is present in fish and some genes known to be under its control can be up-regulated by mammalian PXR ligands. Despite this, direct involvement of PXR in drug biotransformation in fish has yet to be established. Here, the full length PXR sequence was cloned from carp (Cyprinus carpio) and used in a luciferase reporter assay to elucidate its role in xenobiotic metabolism in fish. A reporter assay for human PXR (hPXR) was also established to compare transactivation between human and carp (cPXR) isoforms. Rifampicin activated hPXR as expected, but not cPXR. Conversely, clotrimazole (CTZ) activated both isoforms and was more potent on cPXR, with an EC50 within the range of concentrations of CTZ measured in the aquatic environment. Responses to other azoles tested were similar between both isoforms. A range of pharmaceuticals tested either failed to activate, or were very weakly active, on the cPXR or hPXR. Overall, these results indicate that the cPXR may differ from the hPXR in its responses and/or sensitivity to induction by different environmental chemicals, with implications for risk assessment because of species differences.

Fish can be exposed to a complex mixture of chemical contaminants, including pharmaceuticals, present in discharges of wastewater treatment works (WwTWs) effluents. There is little information on the effects of effluent exposure on fish metabolism, especially the small molecule signaling compounds which are the biological target of many pharmaceuticals. We applied a newly developed sensitive nanoflow-nanospray mass spectrometry nontargeted profiling technique to identify changes in the exposome and metabolome of roach (Rutilus rutilus) exposed to a final WwTWs effluent for 15 days. Effluent exposure resulted in widespread reduction (between 50% and 90%) in prostaglandin (PG) profiles in fish tissues and plasma with disruptions also in tryptophan/serotonin, bile acid and lipid metabolism. Metabolite disruptions were not explained by altered expression of genes associated with the PG or tryptophan metabolism. of the 31 pharmaceutical metabolites that were detected in the effluent exposome of fish, 6 were nonsteroidal anti-inflammatory drugs but with plasma concentrations too low to disrupt PG biosynthesis. PGs, bile acids, and tryptophan metabolites are important mediators regulating a diverse array of physiological systems in fish and the identity of wastewater contaminants disrupting their metabolism warrants further investigation on their exposure effects on fish health.

Estrogens play fundamental roles in regulating reproductive activities and they act through estrogen receptor (ESR) in all vertebrates. Most vertebrates have two ESR subtypes (ESR1 and ESR2), whereas teleost fish have at least three (Esr1, Esr2a and Esr2b). Intricate functionalization has been suggested among the Esr subtypes, but to date, distinct roles of Esr have been characterized in only a limited number of species. Study of loss-of-function in animal models is a powerful tool for application to understanding vertebrate reproductive biology. In the current study, we established esr1 knockout (KO) medaka using a TALEN approach and examined the effects of Esr1 ablation. Unexpectedly, esr1 KO medaka did not show any significant defects in their gonadal development or in their sexual characteristics. Neither male or female esr1 KO medaka exhibited any significant changes in sexual differentiation or reproductive activity compared with wild type controls. Interestingly, however, estrogen-induced vitellogenin gene expression, an estrogen-responsive biomarker in fish, was limited in the liver of esr1 KO males. Our findings, in contrast to mammals, indicate that Esr1 is dispensable for normal development and reproduction in medaka. We thus provide an evidence for estrogen receptor functionalization between mammals and fish. Our findings will also benefit interpretation of studies into the toxicological effects of estrogenic chemicals in fish.

Some fish populations inhabiting contaminated environments show evidence of increased chemical tolerance, however the mechanisms contributing to this tolerance, and whether this is heritable, are poorly understood. We investigated the responses of two populations of wild three-spined stickleback (Gasterosteus aculeatus) with different histories of contaminant exposure to an oestrogen and copper, two widespread aquatic pollutants. Male stickleback originating from two sites, the River Aire, with a history of complex pollution discharges, and Siblyback Lake, with a history of metal contamination, were depurated and then exposed to copper (46μg/L) and the synthetic oestrogen ethinyloestradiol (22ng/L). The hepatic transcriptomic response was compared between the two populations and to a reference population with no known history of exposure (Houghton Springs, Dorset). Gene responses included those typical for both copper and oestrogen, with no discernable difference in response to oestrogen between populations. There was, however, some difference in the magnitude of response to copper between populations. Siblyback fish showed an elevated baseline transcription of genes encoding metallothioneins and a lower level of metallothionein induction following copper exposure, compared to those from the River Aire. Similarly, a further experiment with an F1 generation of Siblyback fish bred in the laboratory found evidence for elevated transcription of genes encoding metallothioneins in unexposed fish, together with an altered transcriptional response to 125μg/L copper, compared with F1 fish originating from the clean reference population exposed to the same copper concentration. These data suggest that the stickleback from Siblyback Lake have a differential response to copper, which is inherited by the F1 generation in laboratory conditions, and for which the underlying mechanism may include an elevation of baseline transcription of genes encoding metallothioneins. The genetic and/or epigenetic mechanisms contributing to this inherited alteration of metallothionein transcription have yet to be established.

In conjunction with the second International Environmental Omics Symposium (iEOS) conference, held at the University of Liverpool (United Kingdom) in September 2014, a workshop was held to bring together experts in toxicology and regulatory science from academia, government and industry. The purpose of the workshop was to review the specific roles that high-content omics datasets (eg, transcriptomics, metabolomics, lipidomics, and proteomics) can hold within the adverse outcome pathway (AOP) framework for supporting ecological and human health risk assessments. In light of the growing number of examples of the application of omics data in the context of ecological risk assessment, we considered how omics datasets might continue to support the AOP framework. In particular, the role of omics in identifying potential AOP molecular initiating events and providing supportive evidence of key events at different levels of biological organization and across taxonomic groups was discussed. Areas with potential for short and medium-term breakthroughs were also discussed, such as providing mechanistic evidence to support chemical read-across, providing weight of evidence information for mode of action assignment, understanding biological networks, and developing robust extrapolations of species-sensitivity. Key challenges that need to be addressed were considered, including the need for a cohesive approach towards experimental design, the lack of a mutually agreed framework to quantitatively link genes and pathways to key events, and the need for better interpretation of chemically induced changes at the molecular level. This article was developed to provide an overview of ecological risk assessment process and a perspective on how high content molecular-level datasets can support the future of assessment procedures through the AOP framework.

In vertebrates, estrogens play fundamental roles in regulating reproductive activities through estrogen receptors (ESRs), and disruption of estrogen signaling is now of global concern for both wildlife and human health. To date, ESRs of only a limited number of species have been characterized. We investigated the functional diversity and molecular basis or ligand sensitivity of ESRs among ray-finned fish species (Actinopterygii), the most variable group within vertebrates. We cloned and characterized ESRs from several key species in the evolution of ray-finned fish including bichir (Polypteriformes, ESR1 and ESR2) at the basal lineage of ray-finned fish, and arowana (Osteoglossiformes, ESR1 and ESR2b) and eel (Anguilliformes, ESR1, ESR2a and ESR2b) both belonging to ancient early-branching lineages of teleosts, and suggest that ESR2a and ESR2b emerged through teleost-specific whole genome duplication, but an ESR1 paralogue has been lost in the early lineage of euteleost fish species. All cloned ESR isoforms showed similar responses to endogenous and synthetic steroidal estrogens, but they responded differently to non-steroidal estrogenic endocrine disrupting chemicals (EDCs) (e.g. ESR2a exhibits a weaker reporter activity compared with ESR2b). We show that variation in ligand sensitivity of ESRs can be attributed to phylogeny among species of different taxonomic groups in ray-finned fish. The molecular information provided contributes both to understanding of the comparative role of ESRs in the reproductive biology of fish and their comparative responses to EDCs.

Various receptor bioassays, including estrogens, androgens and thyroid hormones, have been developed and applied successfully for assessing hormone function in a wide range of animal species, including fish. In fish, corticosteroids play a pivotal role in physiology as they do in mammals, but far less is known about the corticosteroid receptor system in fish compared with in mammals. Here we established a transient transactivation assay using the Japanese medaka, Oryzias latipes, glucocorticoid receptors (olGRs) and mineralocorticoid receptor to analyse their functional properties in a fish. We found that olGR2 was highly responsive to glucocorticoids, similar to the human GR, whereas the olGR1 subtype was minimally responsive. Thus, olGR2 most likely mediates glucocorticoid signaling in medaka. We further tested crosstalk between GRs and other steroid hormones, and found that progestins could activate or inactivate olGR2-mediating transcription, depending on the presence or absence of cortisol. The transactivation assays developed for medaka GRs provide tools to gain useful insights into corticosteroid signaling in fish and for in vitro screening of environmental substances activating GRs.

Exposure to environmental estrogens in wastewater treatment works (WwTW) effluents induces feminized responses in male fish, including the development of eggs in male testes. However, the impacts on the offspring of exposed fish are not well understood. In this study, we examined whether roach (Rutilus rutilus) from mothers that had been exposed to an undiluted WwTW effluent from early life to sexual maturity had altered susceptibility to gonadal feminization and an impaired capacity to reproduce. For males from both WwTW effluent exposed mothers and dilution water exposed mothers, effluent exposure for up to 3 years and 9 months induced feminized male gonads, although the intersex condition was relatively mild. There was no difference in the severity of gonadal feminization in roach derived from either WwTW effluent exposed or dilution water exposed mothers. Furthermore, a breeding study revealed that roach with effluent-exposed mothers reproduced with an equal success as roach with mothers exposed to clean water. Roach exposed to the effluent for 3 years in this study were able to reproduce successfully. Our findings provide no evidence for impacts of WwTW effluent exposure on reproduction or gonadal disruption in roach down the female germ line and add to existing evidence that male roach with a mild intersex condition are able to breed competitively.

In mammals, the peroxisome proliferator-activated receptor α (PPARα) plays a key role in regulating various genes involved in lipid metabolism, bile acid synthesis and cholesterol homeostasis, and is activated by a diverse group of compounds collectively termed peroxisome proliferators (PPs). Specific PPs have been detected in the aquatic environment; however little is known on their pharmacological activity in fish. We investigated the bioavailability and persistence of the human PPARα ligand clofibric acid (CFA) in carp, together with various relevant endpoints, at a concentration similar to therapeutic levels in humans (20mg/L) and for an environmentally relevant concentration (4μg/L). Exposure to pharmacologically-relevant concentrations of CFA resulted in increased transcript levels of a number of known PPARα target genes together with increased acyl-coA oxidase (Acox1) activity, supporting stimulation of lipid metabolism pathways in carp which are known to be similarly activated in mammals. Although Cu,Zn-superoxide dismutase (Sod1) activity was not affected, mRNA levels of several biotransformation genes were also increased, paralleling previous reports in mammals and indicating a potential role in hepatic detoxification for PPARα in carp. Importantly, transcription of some of these genes (and Acox1 activity) were affected at exposure concentrations comparable with those reported in effluent discharges. Collectively, these data suggest that CFA is pharmacologically active in carp and has the potential to invoke PPARα-related responses in fish exposed in the environment, particularly considering that CFA may represent just one of a number of PPAR-active compounds present to which wild fish may be exposed.

Sexual disruption is reported in wild fish populations living in freshwaters receiving discharges of wastewater treatment works (WwTW) effluents and is associated primarily with the feminisation of males by exposure to oestrogenic chemicals. Antiandrogens could also contribute to the feminisation of male fish, but there are far less data supporting this hypothesis and almost nothing is known for the effects of oestrogens in combination with antiandrogens in fish. We conducted a series of in vivo exposures in two fish species to investigate the potency on reproductive-relevant endpoints of the antiandrogenic antimicrobials triclosan (TCS), chlorophene (CP) and dichlorophene (DCP) and the resin, abietic acid (AbA), all found widely in WwTW effluents. We also undertook exposures with a mixture of antiandrogens and a mixture of antiandrogens in combination with the oestrogen 17α-ethinyloestradiol (EE2). In stickleback (Gasterosteus aculeatus), DCP showed a tendency to reduce spiggin induction in females androgenised by dihydrotestosterone (DHT), but these findings were not conclusive. In roach (Rutilus rutilus), exposures to DCP (178 days), or a mixture of TCS, CP and AbA (185 days), or to the model antiandrogen flutamide (FL, 178 days) had no effect on gonadal sex ratio or on the development of the reproductive ducts. Exposure to EE2 (1.5ng/L, 185 days) induced feminisation of the ducts in 17% of the males and in the mixture of antiandrogens (TCS, CP, AbA) in combination with EE2, almost all (96%) of the males had a feminised reproductive ducts. In stickleback androgen receptor (ARα and ARβ) transactivation assays, the model antiandrogens, FL and procymidone inhibited 11-ketotestosterone (11-KT) induced receptor activation, but none of the human antiandrogens, TCS, CP, DCP and AbA had an effect. These data indicate that antimicrobial antiandrogens in combination can contribute to the feminisation process in exposed males, but they do not appear to act through the androgen receptor in fish.

Exposure to endocrine disrupting chemicals (EDCs) can elicit adverse effects on development, sexual differentiation, and reproduction in fish. Teleost species exhibit at least three subtypes of estrogen receptor (ESR), ESR1, ESR2a, and ESR2b; thus, estrogenic signaling pathways are complex. We applied in vitro reporter gene assays for ESRs in five fish species to investigate the ESR subtype-specificity for better understanding the signaling pathway of estrogenic EDCs. Responses to bisphenol A, 4-nonylphenol, and o,p′-DDT varied among ESR subtypes, and the response pattern of ESRs was basically common among the different fish species. Using a computational in silico docking model and through assays quantifying transactivation of the LBD (using GAL-LBD fusion proteins and chimera proteins for the ESR2s), we found that the LBD of the different ESR subtypes generally plays a key role in conferring responsiveness of the ESR subtypes to EDCs. These results also indicate that responses of ESR2s to EDCs cannot necessarily be predicted from the LBD sequence alone, and an additional region is required for full transactivation of these receptors. Our data thus provide advancing understanding on receptor functioning for both basic and applied research.

Current metabolite profiling methods based on liquid chromatography-mass spectrometry (LC-MS) platforms do not detect many of the components present at trace concentrations in extracts of plasma due to their low ionisation efficiency or to interference from highly abundant compounds. Nanoflow LC-nanospray MS platforms, which are commonly used in proteomics, could overcome these limitations and significantly increase analytical sensitivity and coverage of the plasma (xeno)metabolome (i.e. metabolites and xenobiotics), but require small injection volumes (94% of the predominant phospholipid/lysophospholipid species from plasma, whilst absolute recoveries of 63 selected (xeno)metabolites from spiked plasma were generally between 60 and 104%. After a further SPE step, recoveries of test compounds were between 50 and 81%. Studies revealed that both the sample preparation methodology and nUHPLC-nESI-TOFMS analyses gave acceptable repeatability. A qualitative comparison of SPE methods revealed that sample concentration by either polymer or mixed mode ion-exchange SPE gave comprehensive metabolite coverage of plasma extracts, but the use of cation exchange SPE significantly increased detection of many cationic compounds in the sample extracts. Method detection limits for steroid, eicosanoid and bile metabolites were

Clotrimazole (CTZ) is a persistent imidazole antifungal agent which is frequently detected in the aquatic environment and predicted to bio-concentrate in fish. Common carp (Cyprinus carpio) were exposed to mean measured concentrations of either 1.02 or 14.63μgl(-1) CTZ for 4 and 10 days, followed by a depuration period of 4 days in a further group of animals. Following each exposure regimen, plasma and liver CTZ concentrations were measured. Mean measured plasma concentrations of CTZ in animals exposed to the lower concentration of CTZ were 30 and 44μgl(-1) on days 4 and 10, respectively, and in the higher concentration were 318 and 336μgl(-1). Mean measured liver levels in the same animals were 514, 1725, 2111 and 7017μgl(-1) suggesting progressive hepatic accumulation. Measurement of CTZ in plasma after depuration suggested efficient elimination within 4 days, but appreciable levels of CTZ remained in the liver after depuration suggesting a degree of persistence in this tissue. In addition we measured responses of a number of key hepatic detoxification gene targets in the liver associated with the transcription factor pregnane X receptor (PXR); namely cyp450s 2k and 3a, glutathione-S-transferases a and p (gsta and p), and drug transporters multidrug resistance protein1 (mdr1), and MDR-related protein2 (mrp2). CTZ is a potent ligand of the PXR in humans and there is some evidence of PXR activation following exposure to CTZ in fish. The highest concentration of CTZ was adopted to explore the potential for alterations to detoxification gene expression in fish at a pharmacologically relevant dose level, and the lower concentration is within the range reported in effluents from waste water treatment works (WWTW). The genes for all biotransformation enzymes were up-regulated after exposure to the higher concentration of CTZ for 10 days, and alterations in expression occurred for the drug transporter genes mdr1 and mrp2 following exposure to the lower concentration of 1.02μgl(-1) CTZ (mean measured concentration). These data support the potential for CTZ to induce alterations in biotransformation and drug transporter genes associated with PXR in fish at concentrations measured in some WWTW effluents.

Exposure to estrogenic endocrine disrupting chemicals (EDCs) induces a range of adverse effects, notably on reproduction and reproductive development. These responses are mediated via estrogen receptors (ERs). Different species of fish may show differences in their responsiveness to environmental estrogens but there is very limited understanding on the underlying mechanisms accounting for these differences. We used custom developed in vitro ERα reporter gene assays for nine fish species to analyze the ligand- and species-specificity for 12 environmental estrogens. Transcriptonal activities mediated by estradiol-17β (E2) were similar to only a 3-fold difference in ERα sensitivity between species. Diethylstilbestrol was the most potent estrogen (∼10-fold that of E2) in transactivating the fish ERαs, whereas equilin was about 1 order of magnitude less potent in all species compared to E2. Responses of the different fish ERαs to weaker environmental estrogens varied, and for some considerably. Medaka, stickleback, bluegill and guppy showed higher sensitivities to nonylphenol, octylphenol, bisphenol a and the DDT-metabolites compared with cyprinid ERαs. Triclosan had little or no transactivation of the fish ERαs. By constructing ERα chimeras in which the AF-containing domains were swapped between various fish species with contrasting responsiveness and subsequent exposure to different environmental estrogens. Our in vitro data indicate that the LBD plays a significant role in accounting for ligand sensitivity of ERα in different species. The differences seen in responsiveness to different estrogenic chemicals between species indicate environmental risk assessment for estrogens cannot necessarily be predicted for all fish by simply examining receptor activation for a few model fish species. © 2014 American Chemical Society.

Environmental metabolomics is increasingly used to investigate organismal responses to complex chemical mixtures, including waste water effluent (WWE). In parallel, increasingly sensitive analytical methods are being used in metabolomics studies, particularly mass spectrometry. This introduces a considerable, yet overlooked, challenge that high analytical sensitivity will not only improve the detection of endogenous metabolites in biological specimens but also exogenous chemicals. If these often unknown xenobiotic features are not removed from the "biological" dataset, they will bias the interpretation and could lead to incorrect conclusions about the biotic response. Here we illustrate and validate a novel workflow classifying the origin of peaks detected in biological samples as: endogenous, xenobiotics, or metabolised xenobiotics. The workflow is demonstrated using direct infusion mass spectrometry-based metabolomic analysis of testes from roach exposed to different concentrations of a complex WWE. We show that xenobiotics and their metabolic products can be detected in roach testes (including triclosan, chloroxylenol and chlorophene), and that these compounds have a disproportionately high level of statistical significance within the total (bio)chemical changes induced by the WWE. Overall we have demonstrated that this workflow extracts more information from an environmental metabolomics study of complex mixture exposures than was possible previously.

Sex-steroid hormones are essential for normal reproductive activity in both sexes. Estrogens are necessary for ovarian differentiation during a critical developmental stage in vertebrates and promote the growth and differentiation of the female reproductive system. Importantly, environmental estrogens can influence the reproductive system and have been shown to disrupt gametogenesis in males. To understand the molecular mechanisms of estrogen actions and to evaluate estrogen receptor ligand interactions in the carp, Cyprinus carpio, a species used widely for both field- and laboratory-based studies, we cloned all three carp estrogen receptors (ER; ERα, ERβ1 and ERβ2) and applied an estrogen-responsive (ERE)-luciferase reporter assay system to characterize the interactions of these receptors with steroidal and synthetic estrogens. DNA fragments encoding all three ERs in carp, ERα, ERβ1 and ERβ2, were obtained from the ovary using degenerate primer sets and PCR techniques, and full-length carp ER (cER) cDNAs were then obtained using RACE (rapid amplification of the cDNA end) techniques. Amino acid sequences of cERs showed overall homology of 46% (α vs β1), 49% (α vs β2) and 53% (β1 vs β2). In the transient transfection ERE-luciferase reporter assay system (using mammalian cells) the cER proteins displayed estrogen-dependent activation of transcription and cERβ2 showed a higher sensitivity to the natural steroid oestrogen, 17β-estradiol, than cERα. The assay system developed is a powerful assay for toxicology and provides a tool for future studies examining the receptor-environmental chemical interactions and estrogen-disrupting mechanisms in carp. The data presented also expand our knowledge of estrogen receptor evolution. Copyright © 2011 John Wiley & Sons, Ltd. Environmental estrogens can influence the reproductive system and have been shown to disrupt gametogenesis in males. We cloned all three carp Cyprinus carpio, estrogen receptors [ER; ERa, ERb1 and ERb2] and applied a transient transfection ERE-luciferase reporter assay system using mammalian cells. cERb2 showed a higher sensitivity to the natural steroid oestrogen, 17b-estradiol, than cERa. This is a powerful assay for toxicology, and provides a tool for future studies examining the receptor-environmental chemical interactions and estrogen disrupting mechanisms in carp. © 2011 John Wiley & Sons, Ltd.

Evolutionary theory predicts that male and female offspring should be produced at a 1:1 ratio, but this may rarely be the case for species in which sex is determined during incubation by temperature, such as marine turtles. Estimates of primary sex ratio suggest that marine turtle sex ratios are highly skewed, with up to 9 females per male. We captured juvenile hawksbill turtles Eretmochelys imbricata in waters around Anegada, British Virgin Islands, a regionally important foraging aggregation, and analysed concentrations of plasma testosterone and oestradiol- 17β from 62 turtles to estimate sex ratio. There were 2.4 to 7.7 times more females than males. Testosterone concentrations correlated with sampling date and sea surface temperature (SST), with higher con centrations in the late summer when SST was highest, suggesting that assigning sex through threshold values of sex hormones must be carried out cautiously. The sex ratio in the juvenile foraging aggregation around Anegada is more male biased than at other locations, suggesting that turtles at Anegada have resilience against feminising effects of climate change. Future work should (1) integrate the relative contributions of different genetic stocks to foraging aggregations and (2) investigate the annual and seasonal cycles of sex hormones, and differences among individuals and life history stages. © Inter-Research 2013.

Silver nanoparticles cause toxicity in exposed organisms and are an environmental health concern. The mechanisms of silver nanoparticle toxicity, however, remain unclear. We examined the effects of exposure to silver in nano-, bulk-, and ionic forms on zebrafish embryos (Danio rerio) using a Next Generation Sequencing approach in an Illumina platform (High-Throughput SuperSAGE). Significant alterations in gene expression were found for all treatments and many of the gene pathways affected, most notably those associated with oxidative phosphorylation and protein synthesis, overlapped strongly between the three treatments indicating similar mechanisms of toxicity for the three forms of silver studied. Changes in oxidative phosphorylation indicated a down-regulation of this pathway at 24 h of exposure, but with a recovery at 48 h. This finding was consistent with a dose-dependent decrease in oxygen consumption at 24 h, but not at 48 h, following exposure to silver ions. Overall, our data provide support for the hypothesis that the toxicity caused by silver nanoparticles is principally associated with bioavailable silver ions in exposed zebrafish embryos. These findings are important in the evaluation of the risk that silver particles may pose to exposed vertebrate organisms.

Environmental estrogens can influence the reproductive system and have been shown to disrupt gametogenesis in males. We cloned all three carp Cyprinus carpio, estrogen receptors [ER; ERa, ERb1 and ERb2] and applied a transient transfection ERE-luciferase reporter assay system using mammalian cells. cERb2 showed a higher sensitivity to the natural steroid oestrogen, 17b-estradiol, than cERa. This is a powerful assay for toxicology, and provides a tool for future studies examining the receptor-environmental chemical interactions and estrogen disrupting mechanisms in carp.

Exposure to estrogenic chemicals discharged into the aquatic environment has been shown to induce feminization in wild freshwater fish and although fish species have been reported to differ in their susceptibility for these effects, empirical studies that directly address this hypothesis are lacking. In this study, in vitro ERα activation assays were applied in a range of fish species used widely in chemical testing (including, zebrafish, fathead minnow, medaka) and/or as environmental monitoring species (including, roach, stickleback, carp) to assess their comparative responsiveness to natural (estrone, estradiol, estriol) and synthetic (17α-ethinylestradiol (EE2), diethylstilbestrol (DES)) estrogens. In vivo exposures to EE2 via the water (nominal 2 and 10 ng/L for 7 days) were also conducted for seven fish species to compare their responsiveness for hepatic vitellogenin (VTG) mRNA induction (an ER mediated response). of the fish species tested, zebrafish ERα was found to be the most responsive and carp and stickleback ERα the least responsive to natural steroid estrogens. This was also the case for exposure to EE2 with an ERα-mediated response sensitivity order of zebrafish > medaka > roach > fathead minnow > carp > stickleback. For VTG mRNA induction in vivo, the order of species responsiveness was: rainbow trout (not tested in the ERα activation assays) > zebrafish > fathead minnow > medaka > roach > stickleback > carp. Overall, the responses to steroid estrogens in vitro via ERα compared well with those seen in vivo (VTG induction for exposure to EE2) showing in vitro screening of chemicals using fish ERα-mediated responses indicative of estrogenic responses (VTG induction) in vivo.

Fish in many surface freshwaters are exposed to a range of pharmaceuticals via wastewater treatment works effluent discharges. In mammals the pregnane X receptor (PXR) plays a key role in the regulation of a suite of genes involved in drug biotransformation, but information on the role of this response pathway in fish is limited. Here we investigated the effects of exposure of carp (Cyprinus carpio) primary hepatocytes to the human PXR agonist rifampicin (RIF) on expression of target genes involved in phase I (cyp2k, cyp3a) and phase II (gstα, gstπ) drug metabolism and drug transporters mdr1 and mrp2. RIF induced expression of all target genes measured and the PXR antagonist ketoconazole (KET) inhibited responses of cyp2k and cyp3a. Exposure of the primary carp hepatocytes to the pharmaceuticals ibuprofen (IBU), clotrimazole (CTZ), clofibric acid (CFA) and propranolol (PRP), found responses to IBU and CFA, but not CTZ or PRP. This is in contrast with mammals, where CTZ is a potent PXR-agonist. Collectively our data indicate potential PXR involvement in regulating selected genes involved in drug metabolism in fish, but suggest some divergence in the regulation pathways with those in mammals. The carp primary hepatocyte model serves as a useful system for screening for responses in these target genes involved in drug metabolism.

Organisms exposed to wastewater treatment works (WwTW) effluents accumulate complex mixtures of xenobiotics but there is a scarcity of information on the nature and impacts of these chemical mixtures. We applied metabolomics techniques as a novel approach to identify xenobiotics and their metabolites (the xenometabolome) that bioconcentrate in fish exposed to a WwTW effluent. Exposed juvenile rainbow trout (Oncorhynchus mykiss) accumulated surfactants, naphthols, chlorinated xylenols, and phenoxyphenols, chlorophenes, resin acids, mefenamic acid, oxybenzone, and steroidal alkaloids in the bile or plasma, and there were perturbations in the plasma concentrations of bile acids and lipids. Exposure of adult roach (Rutilus rutilus) to 50% or 100% concentrations of the same effluent resulted in dose-dependent increases in plasma concentrations of xenometabolites as well as cyprinol sulfate and taurocholic acid, lysophospholipids, and a decrease in sphingosine levels (a key component of cell membrane lipids). Our findings reveal the highly complex nature of xenobiotics accumulating in effluent-exposed fish, and the great potential of metabolomics for both identifying plasma marker (bio)chemicals for monitoring exposure to wastewater effluents, and for targeting studies on potential consequent impacts on fish health.

The widespread occurrence of feminized male fish downstream of some UK Wastewater Treatment Works (WwTWs) has been associated with exposure to estrogenic and potentially antiandrogenic (AA) contaminants in the effluents. In this study, profiling of AA contaminants in WwTW effluents and fish was conducted using HPLC in combination with in vitro androgen receptor transcription screens. Analysis of extracts of wastewater effluents revealed complex profiles of AA activity comprising 21-53 HPLC fractions. Structures of bioavailable antiandrogens were identified by exposing rainbow trout to a WwTW effluent and profiling the bile for AA activity using yeast (anti-YAS) and mammalian-based (AR-CALUX) androgen receptor transcription screens. The predominant fractions with AA activity in both androgen receptor screens contained the germicides chlorophene and triclosan, and together these contaminants accounted for 51% of the total anti-YAS activity in the fish bile. Other AA compounds identified in bile included chloroxylenol, dichlorophene, resin acids, napthols, oxybenzone, 4-nonylphenol, and bisphenol A. Pure standards of these compounds were active in the androgen receptor screens at potencies relative to flutamide of between 0.1 and 13.0. Thus, we have identified, for the first time, a diverse range of AA chemicals in WwTWs that are bioavailable to fish and which need to be assessed for their risk to the reproductive health of these organisms and other aquatic biota. © 2011 American Chemical Society.

Feminized responses are widespread in wild populations of roach, Rutilus rutilus, living in UK rivers, and some of these responses have been shown to arise as a consequence of exposure to wastewater treatment works (WwTW) effluent discharges and the endocrine disrupting chemicals (EDCs) they contain. The causation of the ovotestis condition in wild roach, however, has yet to be established. Furthermore, the impact of long-term exposure to WwTW effluents on the reproductive fitness of wild fish populations is not known, and this information is crucial for population level effect assessments. We undertook a chronic exposure of roach to a treated estrogenic wastewater effluent for up to 3.5 years to assess principally for effects on subsequent reproductive fitness, as determined through parentage analysis on offspring from a competitive breeding study. In generating the fish for the breeding study we found that exposure to full strength WwTW effluent until sexual maturity resulted in sex reversal in almost all males in the population; 98% of the exposed fish were phenotypic females, containing ovaries. Furthermore, fish exposed to a 50% dilution of WwTW effluent contained ovotestis (21% of the male roach) that was absent from the control population. In competitive breeding studies, and applying DNA microsatellites to assess parentage, we show that presumptive females exposed to sexual maturity to WwTW effluent bred normally, albeit in the absence of nonexposed females, but putative sex-reversed males breeding as females contributed poorly, if at all, in a breeding population, depending on the competition. These novel findings on sex reversal add a new dimension for impact assessments of exposure to WwTW effluents on fish populations.

The ability of targeted and nontargeted metabolomics to discover chronic ecotoxicological effects is largely unexplored. Fenitrothion, an organophosphate pesticide, is categorized as a "red list" pollutant, being particularly hazardous to aquatic life. It acts primarily as a cholinesterase inhibitor, but evidence suggests it can also act as an androgen receptor antagonist. Whole-organism fenitrothion-induced toxicity is well-established, but information regarding target and off-target molecular toxicities is limited. Here we study the molecular responses of male roach (Rutilus rutilus) exposed to fenitrothion, including environmentally realistic concentrations, for 28 days. Acetylcholine was assessed in brain; steroid metabolism was measured in testes and plasma; and NMR and mass spectrometry-based metabolomics were conducted on testes and liver to discover off-target toxicity. O-demethylation was confirmed as a major route of pesticide degradation. Fenitrothion significantly depleted acetylcholine, confirming its primary mode of action, and 11-ketotestosterone in plasma and cortisone in testes, showing disruption of steroid metabolism. Metabolomics revealed significant perturbations to the hepatic phosphagen system and previously undocumented effects on phenylalanine metabolism in liver and testes. On the basis of several unexpected molecular responses that were opposite to the anticipated acute toxicity, we propose that chronic pesticide exposure induces an adapting phenotype in roach, which may have considerable implications for interpreting molecular biomarker responses in field-sampled fish. © 2011 American Chemical Society.

Many factors have been considered in evaluations of the risk-benefit balance of hormone replacement therapy (HRT), used for treating menopausal symptoms in women, but not its potential risks for the environment We investigated the possible environmental health implications of conjugated equine estrogens (CEEs), the most common components of HRT, including their discharge into the environment, their uptake, potency, and ability to induce biological effects in wildlife. Influents and effluents from four U.K. sewage treatment works (STWs), and bile of effluent-exposed fish, were screened for six equine estrogens. In vitro estrogen receptor (ER) activation assays were applied in humans and fish to compare their potencies, followed by in vivo exposures of fish to equine estrogens and evaluation of bioaccumulation, estrogenic responses, and ER gene expression. The equine estrogen equilenin (Eqn), and its metabolite 17beta-dihydroequilenin (17beta-Eqn), were detected by tandem GC-MSMS in all STW influent samples and 83% of STW effluent samples analyzed, respectively, at low concentrations (0.07-2.6 ng/L) and were taken-up into effluent-exposed fish. As occurs in humans, these estrogens bound to and activated the fish ERs, with potencies at ERalpha 2.4-3490% of thatfor 17beta-estradiol. Exposure of fish for 21 days to Eqn and 17beta-Eqn induced estrogenic responses including hepatic growth and vitellogenin production at concentrations as low as 0.6-4.2 ng/L. Associated with these effects were inductions of hepatic ERalpha and ERbeta1 gene expression, suggesting ER-mediated mechanism(s) of action. These data provide evidence for the discharge of equine estrogens from HRT into the aquatic environment and highlight a strong likelihood that these compounds contribute to feminization in exposed wildlife.

The presence of endocrine disrupting chemicals (EDCs) in the environment has driven the development of screening and testing assays to both identify chemicals with hormonal activity and evaluate their potential to cause adverse effects. As the number of animals used for research and regulatory purposes rises, and set against a desire to reduce animal testing, there is increased emphasis on the development and application of in vitro techniques to evaluate chemical risks to the environment. Induction of vitellogenin (VTG) in isolated fish liver cells has been used successfully to identify a wide range of EDCs, including both natural and synthetic oestrogens and a variety of other xenoestrogens. However, the vitellogenic response reported for hepatocytes in culture has been shown to vary widely, making comparisons between studies difficult. The work presented in this paper explored the variability of the vitellogenic response in primary cultures of common carp (Cyprinus carpio) hepatocytes following exposure to the model oestrogenic compound, 17beta-oestradiol (E2). As expected, variability in the vitellogenic response was observed, both in terms of the sensitivity and magnitude of VTG induction, for hepatocytes isolated from different fish. An apparent difference was observed in the response of isolated hepatocytes based on the sex of the donor fish; maximum levels of E2-stimulated VTG synthesis in hepatocytes derived from females appeared higher (1962 ng mL(-1)+/-487 [n=9] compared with 1194 ng mL(-1)+/-223 for hepatocytes from males [n=9]) and EC(50) values lower (1.61+/-0.4 microM E2 for females and 2.12+/-0.2 microM E2 for males). However, these differences were not statistically significant, likely in part due to the variation observed in the vitellogenic response. In particular, hepatocytes derived from female fish showed more variation than their male counterparts (the co-efficient of variation for females was 77% compared to 28% for males). Despite the variation observed in the vitellogenic response between different cultures, data from the different donor fish could be compared by standardising responses relative to the maximum VTG induction in each culture following exposure to E2. Adopting this approach in the future will allow for data from different hepatocyte cultures and from donor fish of different sexes, age and stage of maturity to be compared with greater consistency. Measurement of vtg mRNA expression was relatively more sensitive to the oestrogenic effects of E2 exposure than measurement of VTG protein (the LOEC at the transcriptome level was 10-fold lower [0.01 microM E2] than at the protein level [0.1 microM E2]) and changes in vtg mRNA expression showed less variation between individual hepatocyte isolations. Measurement of vtg mRNA in the hepatocyte culture system therefore may offer the most sensitive and consistent option for the screening of chemicals with oestrogenic activity in fish primary hepatocyte cultures.

Globally, feminization responses in wild male freshwater fish are caused by exposure to estrogenic chemicals, including natural and synthetic estrogens, contained in effluentsfromwastewater treatment works. In U.K. rivers, feminization responses, including intersex, are widespread in wild roach (Rutilus rutilus) populations, and severely affected fish have a reduced reproductive success. We exposed roach to environmentally relevant concentrations of the contraceptive estrogen 17alpha-ethinylestradiol (EE2) for up to 2 years, including intermittent and repeated exposures,to determine effects on sexual development and subsequent responsiveness to estrogen. Exposure of roach to EE2 (at 4 ng/L) for 2 years resulted in sex reversal in males, leading to an all-female population with two cohorts in terms of their stages of ovarian development one paralleling the control females and one at a significantly less advanced stage, which we propose were sex-reversed males. Differing developmental and maturing rates of the putative sex-reversed males compared with control females would question their functional capability as females in the wild. Early-life exposure to environmentally relevant concentrations of EE2 sensitized females to estrogen, as determined by the measurement of the responses of estrogen-sensitive genes in a further EE2 challenge 398 days after the original exposure. In the wild, exposure to environmentally relevant concentrations of EE2 during early life has significantly wider implications for the sexual physiology in fish than has thus far been determined.

Wild roach (Rutilus rutilus) inhabiting UK rivers contaminated with estrogenic effluents from wastewater treatment works show altered sexual development, including intersex, and this can impact negatively on their reproductive capabilities. The molecular events underlying these disruptions in gender assignment, however, are still poorly understood. In this study, two isoforms of aromatase (cyp19a1a and cyp19a1b) were cloned from the roach, and effects of exposure to 17alpha-ethinylestradiol (EE(2)) during early life were determined on the expression of both aromatases and on the estrogen receptors (ERs) (subtypes esr1 and esr2b) and analyzed against effects on the progression of gonadal sex differentiation. Exposure to environmentally relevant concentrations of EE(2) during the critical period of sex differentiation resulted in gonadal feminization and all roach exposed to 4 ng EE(2)/l were females. These effects on gonadal development were associated with alterations in the expression of both esr and cyp19a1 genes in bodies and heads of exposed fish with the most marked effects on the expression of esr1 and cyp19a1b. Our findings show that both aromatase isoforms and both ER subtypes are associated with sexual differentiation in roach, and alterations in their expression can signal for disruptions in sexual development.

In mammals, the Kiss1 receptor (Kiss1r) and its kisspeptin ligands are key factors regulating the onset of puberty. In fish, however, the mechanisms underlying the initiation of puberty are poorly understood and the role of the Kiss1r/kisspeptin pathway in this process has not been established. In this study, a bioinformatics approach was used to identify the genes for Kiss1 and Kiss1r in five teleost genomes and the information used to clone the corresponding transcripts from zebrafish. Zebrafish kiss1r was expressed predominantly in the brain, with a minor level of expression in the eye, and zebrafish kiss1 was expressed in brain, intestine, adipose tissue and testis. Analysis of the chromosome region containing the kiss1 locus showed high synteny across vertebrate genomes. In contrast to their mammalian homologues, teleost Kiss1 protein sequences were poorly conserved with the exception of the region representing kisspeptin-10. Signal peptide sequences and likely cleavage and amidation sites in the teleost Kiss1 sequences were determined and found to be similar to those in mammalian Kiss1. This is the first report of the existence and characterization of the Kiss1 gene outside the mammalian taxa, suggesting that a functional Kiss1/Kiss1 receptor pathway is conserved across vertebrate species.

The roach (Rutilus rutilus) has become a sentinel species for the study of sexual disruption in wild fish populations as a consequence of exposure to endocrine disrupting chemicals (EDCs). Little is known, however, about the normal ontogeny of sexual development in this species. Here, we analyzed the ontogeny of sexual development in captive-bred roach and assessed how growth rate and fish size affected the timing of both sexual differentiation and sexual development over a 2-year period. Ovarian differentiation was first recorded at 68 days post-fertilization (dpf) and this preceded testicular differentiation (first recorded at 98 dpf). In contrast, sexual maturation occurred at an earlier age in males (300 dpf) compared with females (728 dpf). No differences in body size (length or weight) were recorded between male and female roach until the fish were 415 dpf. Studies on three populations of roach which grew at different rates showed that the timing of sexual differentiation was highly variable and more related to fish size than to fish age. Time to sexual maturation was also variable among populations but, subsequent to their first year of life, gonadal status was less well associated with fish size. Interestingly, the sex ratio of the population was biased towards females in populations that grew more rapidly during early life. The findings presented here provide a valuable foundation of work to support both field- and laboratory-based assessments on the effects of EDCs, and other stressors, on sexual differentiation and development in the roach.

Alterations in development and reproduction as a consequence of exposure to endocrine-disrupting chemicals (EDCs) have been demonstrated in many wildlife species. Animals living in, or closely associated with, the aquatic environment are particularly vulnerable to endocrine disruption because thousands of chemicals are actively disposed into rivers, estuaries and seas. Fish have thus been a focus in endocrine disruption studies, and some of the most comprehensive studies on the disruption of sexual development and function are on the roach (Rutilus rutilus). This paper provides a critical analysis of the roach as a sentinel for studies into endocrine disruption. The paper starts by describing what is known on the basic reproductive biology of the roach, information essential for interpreting chemical effect measures on sexual development and function. We then analyze where and how the roach has been applied to improve our understanding of the estrogenic nature of discharges from wastewater treatment works (WWTWs) and describe the phenomenon of feminized male roach in UK rivers. In this paper, the causation of these effects and issues of relative susceptibility and sensitivity of the roach to the effects of estrogenic EDCs are addressed. The paper then describes the ongoing work on the development of genetic and genomic resources for roach and analyses how these are being applied in studies to understand the mechanisms of disruption of sexual development. Finally, the paper addresses the biological significance of sexual disruption and intersex for the individual and discusses the possible implications for wild populations.