Endocrine disrupting chemicals and sexual behaviors in fish – a critical review on effects and possible consequences

Developing an Approach for Integrating Chemical Analysis and Transcriptional Changes to Assess Contaminants in Water, Sediment, and Fish

Pharmaceuticals in aquatic environments pose threats to aquatic organisms because of their continuous release and potential accumulation. Monitoring methods for these contaminants are inadequate, with targeted analyses falling short in assessing water quality's impact on biota. The present study advocates for integrated strategies combining suspect and targeted chemical analyses with molecular biomarker approaches to better understand the risks posed by complex chemical mixtures to nontarget organisms. The research aimed to integrate chemical analysis and transcriptome changes in fathead minnows to prioritize contaminants, assess their effects, and apply this strategy in Wascana Creek, Canada. Analysis revealed higher pharmaceutical concentrations downstream of a wastewater-treatment plant, with clozapine being the most abundant in fathead minnows, showing notable bioavailability from water and sediment sources. Considering the importance of bioaccumulation factor and biota-sediment accumulation factor in risk assessment, these coefficients were calculated based on field data collected during spring, summer, and fall seasons in 2021. Bioaccumulation was classified as very bioaccumulative with values >5000 L kg-1, suggesting the ability of pharmaceuticals to accumulate in aquatic organisms. The study highlighted the intricate relationship between nutrient availability, water quality, and key pathways affected by pharmaceuticals, personal care products, and rubber components. Prioritization of these chemicals was done through suspect analysis, supported by identifying perturbed pathways (specifically signaling and cellular processes) using transcriptomic analysis in exposed fish. This strategy not only aids in environmental risk assessment but also serves as a practical model for other watersheds, streamlining risk-assessment processes to identify environmental hazards and work toward reducing risks from contaminants of emerging concern. Environ Toxicol Chem 2024;43:2252-2273. © 2024 SETAC.

EthoCRED: a framework to guide reporting and evaluation of the relevance and reliability of behavioural ecotoxicity studies

Behavioural analysis has been attracting significant attention as a broad indicator of sub-lethal toxicity and has secured a place as an important subdiscipline in ecotoxicology. Among the most notable characteristics of behavioural research, compared to other established approaches in sub-lethal ecotoxicology (e.g. reproductive and developmental bioassays), are the wide range of study designs being used and the diversity of endpoints considered. At the same time, environmental hazard and risk assessment, which underpins regulatory decisions to protect the environment from potentially harmful chemicals, often recommends that ecotoxicological data be produced following accepted and validated test guidelines. These guidelines typically do not address behavioural changes, meaning that these, often sensitive, effects are not represented in hazard and risk assessments. Here, we propose a new tool, the EthoCRED evaluation method, for assessing the relevance and reliability of behavioural ecotoxicity data, which considers the unique requirements and challenges encountered in this field. This method and accompanying reporting recommendations are designed to serve as an extension of the "Criteria for Reporting and Evaluating Ecotoxicity Data (CRED)" project. As such, EthoCRED can both accommodate the wide array of experimental design approaches seen in behavioural ecotoxicology, and could be readily implemented into regulatory frameworks as deemed appropriate by policy makers of different jurisdictions to allow better integration of knowledge gained from behavioural testing into environmental protection. Furthermore, through our reporting recommendations, we aim to improve the reporting of behavioural studies in the peer-reviewed literature, and thereby increase their usefulness to inform chemical regulation.

Negligible additive effect of environmental concentrations of fragmented polyethylene terephthalate microplastics on the growth and reproductive performance of Java medaka exposed to 17β-estradiol and bisphenol A

To investigate whether environmental concentrations of fragmented polyethylene terephthalate (PET) microplastics (MPs) have additional or combined effects on endocrine-disrupting activity, Java medaka (Oryzias javanicus) were exposed to 17β-estradiol (E2; 5, 10, 50, and 100 ng L-1), bisphenol A (BPA; 5, 10, 50, and 100 µg L-1), and E2 and BPA combined with PET MPs (1 and 100 particles L-1) for 200 days. The growth parameters, such as body length and weight, were significantly decreased by the highest concentrations of E2 and BPA. A significant reduction in egg production was observed in female fish exposed to BPA, with an additive toxic effect of PET MPs. A female-biased sex ratio was observed in fish exposed to both chemicals. Exposure to E2 significantly increased the hepatosomatic index (HSI) in both sexes, while no significant effect was observed in the gonadosomatic index (GSI). Exposure to BPA significantly increased the HSI in female fish and decreased the GSI in both sexes of fish. An additive effect of PET MPs was observed on the GSI value of female exposed to BPA. Significant elevations in vitellogenin (VTG) levels were observed in both sexes due to exposure to E2 and BPA. Additive effects of PET MPs were observed on VTG levels in males exposed to E2 and BPA. Taken together, even long-term treatment with PET MPs induced only a negligible additive effect on the endocrine-disrupting activity in Java medaka at environmentally relevant concentrations.

Zebrafishtracker3D: A 3D skeleton tracking algorithm for multiple zebrafish based on particle matching

Zebrafish are considered as model organisms in biological and medical research because of their high degree of homology with human genes. Automatic behavioral analysis of multiple zebrafish based on visual tracking is expected to improve research efficiency. However, vision-based multi-object tracking algorithms often suffer from data loss owing to mutual occlusion. In addition, simply tracking zebrafish as points is not sufficient-more detailed information, which is required for research on zebrafish behavior. In this paper, we propose Zebrafishtracker3D, which utilizes a skeleton stability strategy to reduce detection error caused by frequent overlapping of multiple zebrafish effectively and estimates zebrafish skeletons using head coordinates in the top view. Further, we transform the front- and top-view matching task into an optimization problem and propose a particle-matching method to perform 3D tracking. The robustness of the algorithm with respect to occlusion is estimated on the dataset comprising two and three zebrafish. Experimental results demonstrate that the proposed algorithm exhibits a multiple object tracking accuracy (MOTA) exceeding 90% in the top view and a 3D tracking matching accuracy exceeding 90% in the complex videos with frequent overlapping. It is noteworthy that each instance in the trace saves its skeleton. In addition, Zebrafishtracker3D is applied in the zebrafish courtship experiment, establishes the stability of the method in applications of life science, and proves that the data can be used for behavioral analysis. Zebrafishtracker3D is the first algorithm that realizes 3D skeleton tracking of multiple zebrafish simultaneously.

Progesterone and brassinosteroids synergistically enhance progesterone removal and antioxidant capacity of Solanum nigrum L

Progesterone (PROG) has been detected at various concentrations in the environment and has adverse effects on humans and wildlife. This work evaluated the impact of PROG in Solanum nigrum L. plants, its removal capacity, and how 2,4-epibrassinolide (24-EBL) affects this process. Three treatments were used: (1) control, (2) irrigation with 0.8 µM PROG, and (3) treatment with 0.8 µM PROG after a pre-treatment with a foliar application of 1 µM 2,4-EBL (PROG/24EBL). After 20 days of treatment, no PROG was detected in the nutrient solution or plant tissues, indicating that the PROG was removed and metabolized. Lipid peroxidation significantly decreased in response to PROG in shoots and roots, and this effect was even more significant for both organs of the PROG/24EBL plants. Additionally, both treatments in both organs showed a decrease in H2O2 levels, and both steroid hormones increased the plants' antioxidant system at both the biochemical and gene expression levels. In conclusion, S. nigrum can swiftly remove PROG without affecting its growth, and the use of 24-EBL synergistically decreases oxidative damage by increasing the activity of the antioxidant system and enhancing plant PROG removal ability.

Effects of metformin on wild fathead minnows (Pimephales promelas) using in-lake mesocosms in a boreal lake ecosystem

Due to its widespread use for the treatment of Type-2 diabetes, metformin is routinely detected in surface waters globally. Laboratory studies have shown that environmentally relevant concentrations of metformin can adversely affect the health of adult fish, with effects observed more frequently in males. However, the potential risk to wild fish populations has yet to be fully elucidated and remains a topic of debate. To explore whether environmentally relevant metformin exposure poses a risk to wild fish populations, the present study exposed wild fathead minnows (Pimephales promelas) to 5 or 50 μg/L metformin via 2 m diameter in-lake mesocosms deployed in a natural boreal lake in Northern Ontario at the International Institute for Sustainable Development - Experimental Lakes Area (IISD-ELA). Environmental monitoring was performed at regular intervals for 8-weeks, with fish length, weight (body, liver and gonad), condition factor, gonadosomatic index, liver-somatic index, body composition (water and biomolecules) and hematocrit levels evaluated at test termination. Metabolic endpoints were also evaluated using liver, brain and muscle tissue, and gonads were evaluated histologically. Results indicate that current environmental exposure scenarios may be sufficient to adversely impact the health of wild fish populations. Adult male fish exposed to metformin had significantly reduced whole body weight and condition factor and several male fish from the high-dose metformin had oocytes in their testes. Metformin-exposed fish had altered moisture and lipid (decrease) content in their tissues. Further, brain (increase) and liver (decrease) glycogen were altered in fish exposed to high-dose metformin. To our knowledge, this study constitutes the first effort to understand metformin's effects on a wild small-bodied fish population under environmentally relevant field exposure conditions.

Sub-acute exposure of male guppies (Poecilia reticulata) to environmentally relevant concentrations of PFOA and GenX induces significant changes in the testis transcriptome and reproductive traits

Poly- and perfluoroalkyl substances (PFAS) are frequently detected in the environment and are linked to adverse reproductive health outcomes in humans. Although legacy PFAS have been phased out due to their toxicity, alternative PFAS are increasingly used despite the fact that information on their toxic effects on reproductive traits is particularly scarce. Here, we exposed male guppies (Poecilia reticulata) for a short period (21 days) to an environmentally realistic concentration (1 ppb) of PFOA, a legacy PFAS, and its replacement compound, GenX, to assess their impact on reproductive traits and gene expression. Exposure to PFAS did not impair survival but instead caused sublethal effects. Overall, PFAS exposure caused changes in male sexual behaviour and had detrimental effects on sperm motility. Sublethal variations were also seen at the transcriptional level, with the modulation of genes involved in immune regulation, spermatogenesis, and oxidative stress. We also observed bioaccumulation of PFAS, which was higher for PFOA than for GenX. Our results offer a comprehensive comparison of these two PFAS and shed light on the toxicity of a newly emerging alternative to legacy PFAS. It is therefore evident that even at low concentrations and with short exposure, PFAS can have subtle yet significant effects on behaviour, fertility, and immunity. These findings underscore the potential ramifications of pollution under natural conditions and their impact on fish populations.

Independent and synergistic effects of microplastics and endocrine-disrupting chemicals on the reproductive social behavior of fathead minnows (Pimephales promelas)

Microplastics (MPs) have become an environmental concern in recent years, with most research focused on the physiological effects of exposure. Comparatively little consideration has been given to the potential behavioral impacts of exposure, which may also have fitness consequences for individuals. Moreover, MPs can serve as vectors for endocrine-disrupting chemicals and other locally co-occurring contaminants known to impair behavioral responses. This project aimed to determine whether MPs alone or in association with a common environmental EDC (17-alpha ethinyl estradiol; EE2) alter reproductive behavior and decision-making in fish. Male and female fathead minnows (Pimephales promelas) were exposed to MPs associated with either a low (10 ng/L; MPEE2 10) or high (50 ng/L, MPEE2 50) concentration of EE2, or MPs without EE2 (MPvirgin) for 30 days via a dietary feeding protocol. Behavioral trials were conducted on Day 31 to determine the effects of exposure on male-female social interactions. The expression of male sexually selected traits, including courtship, was unaffected by exposure. However, non-exposed females in all treatment groups trended toward discrimination against exposed males, which reached statistical significance for the MPEE2 50 group. Female fish exposed to MPs, alone or in association with EE2, were equally likely to approach and associate with non-exposed and exposed males. The results from this study suggest that MPs may alter social behavior in fishes and that the behavioral impacts of exposure may be more strongly pronounced in females than males. Such individual-level changes in fitness have the potential to impact population size, with downstream effects on the broader aquatic community.

Assessment of textile industry effluent (untreated and microbially treated) induced genotoxic, haematological, biochemical, histopathological and ultrastructural alterations in fresh water fish Channa punctata

The unregulated expulsion of untreated textile water into water bodies is a major hazard to aquatic ecosystems. The present investigation was contrived to estimate the impact of textile dye bath effluent (untreated and microbially treated) on fish Channa punctata. Untreated effluent-exposed fish showed extremely altered behaviour (air gulping, erratic and speedy movements, increased opercular activity) and morphology (deposition of dyes on skin and scales, high pigmentation, mucus exudation). Significantly increased micronuclei (1.61-, 1.28-, 1.38-fold) and aberrant cell frequency (1.37-, 1.45-, 1.28-fold) was observed in untreated group as compared to treated group after 15, 30, and 45 days of exposure. Tail length, % tail intensity, tail moment and olive tail moment were also enhanced in all the exposed tissues. However, maximum damage was noticed in gill tissues showing 1.19-, 1.37-, 1.34- and 1.50-fold increased TL, %TI, TM and OTM in untreated group as compared to treated group after 45 days of exposure. On comparing untreated and treated groups, increased blood parameters and significantly reduced white blood cell count (WBC) were noticed in treated group. Significantly enhanced alterations in biochemical parameters were also analysed in untreated group. Reduced alterations in enzymological levels of fishes exposed to treated effluent indicate lesser toxic nature of the degraded metabolites of dye. Histological analysis in fishes exposed to untreated effluent showed several deformities in liver (necrosis, congestion, fusion of cells and melanomacrophage infiltration) and gill tissues (necrosis, bending of lamellae and severe aneurysm). Scanning electron microscopy (SEM) analysis further reaffirmed the pathologies observed in histological analysis. Fewer structural alterations were noticed in treated effluent fishes. The results concluded that untreated effluent inflicted toxicity potential on morphology as well as physiological defects in fish, and the severity increased with increasing duration of exposure, whereas reduction in toxicity in microbially treated groups can be analysed for aquacultural purposes owing to their lesser toxic nature.

Potential risk of estrogenic compounds produced by water blooms to aquatic environment

Some freshwater phytoplankton species have been suggested to produce estrogenic compounds in concentrations which could cause adverse effects to aquatic biota, while other studies showed no estrogenic effects after exposure to phytoplankton extracts or pointed out possible sources of the overestimation of the estrogenic activity. This study aimed to clarify these research inconsistencies by investigating estrogenicity of biomass extracts from both environmental freshwater blooms and laboratory cyanobacterial and algae cultures by in vitro reporter bioassay. Biomasses of 8 cyanobacterial and 3 algal species from 7 taxonomic orders were extracted and tested. Next to this, samples of environmental water blooms collected from 8 independent water bodies dominated by phytoplankton species previously assessed as laboratory cultures were tested. The results showed undetectable or low estrogenicity of both freshwater blooms and laboratory cultures with E2 equivalent concentration (EEQ) in a range from LOQ up to 4.5 ng EEQ/g of dry mass. Moreover, the co-exposure of biomass extracts with environmentally relevant concentration of model estrogen (steroid hormone 17β-estradiol; E2), commonly occurring in surface waters, showed simple additive interaction. However, some of the biomass extracts elicited partially anti-estrogenic effects in co-exposure with higher E2 concentration. In conclusion, our study documents undetectable or relatively low estrogenic potential of biomass extracts from both environmental freshwater blooms and studied laboratory cultured cyanobacterial and algae species. Nevertheless, in case of very high-density water blooms, even this low estrogenicity (detected for two cyanobacterial species) could lead to EEQ content in biomass reaching effect-based trigger values indicating potential risk, if recalculated per water volume at field sites. However, these levels would not occur in water under realistic environmental scenarios and the potential estrogenic effects would be most probably minor compared to other toxic effects caused by massive freshwater blooms of such high densities.

Using Hepatic Gene Expression Assays in English Sole (Parophrys vetulus) to Investigate the Effects of Metro Vancouver Wastewater Effluents

The present study has investigated the effects of Metro Vancouver's wastewater treatment plant (WWTP) effluents on English sole (Parophrys vetulus) hepatic gene expression using novel targeted gene expression assays to complement the 2017 Burrard Inlet Ambient Monitoring Program conducted by Metro Vancouver. Seven locations of varying distance to the WWTPs were included. Twelve genes involved in xenobiotic defense (CYP1A, HSP70), thyroid function (DIO1), lipid and glucose metabolism (FABP1, FASN, GLUT2, PPARδ, PPARγ), protein synthesis (18S rRNA, RPS4X), and reproduction (ERα, VTG) revealed several differences between these impacted sites. A key finding of the present study was that males exhibited VTG transcript levels either equivalent or exceeding female levels of this gene at all sites investigated, indicating widespread exposure of estrogenic contaminants throughout Burrard Inlet. Furthermore, the induction of hepatic CYP1A was observed due to possible downstream sites being subjected to a larger influx of certain planar halogenated and non-halogenated hydrocarbons from multiple industrial contributors. This study also revealed significant differences between the sites examined and in genes involved in transcriptional regulation and synthesis of proteins, lipids and glucose metabolism, and thyroid hormone metabolism. Collectively, this study demonstrates the potential of molecular biomarkers of urban contaminant exposure in wild caught English sole for use in diagnosing a broader range of adverse health effects when combined with conventional whole organism health indicators.

Effects of Dietary Cholesterol Regulation on Spermatogenesis of Gobiocypris rarus Rare Minnow

Cholesterol is an important component of cell membranes, and also a precursor for the synthesis of sex hormones, playing an important role in reproduction. However, few studies have focused on cholesterol and reproductive health. To investigate the toxic effects of different cholesterol levels on the spermatogenesis of rare minnows, we regulate the cholesterol content in fish by feeding them a high-cholesterol diet and cholesterol inhibitor pravastatin, and cholesterol levels, sex hormone (T and 11KT) levels, testis histology, sperm morphology and function, and the expression of genes related to sex hormone synthesis were investigated. The research findings indicate that increasing cholesterol levels significantly increases the liver weight and hepatic-somatic index, as well as the total cholesterol and free cholesterol levels in the testis, liver, and plasma of rare minnow, while inhibiting cholesterol has the opposite effect (p < 0.05). However, both increasing and decreasing cholesterol levels can suppress rare minnow testicular development, as evidenced by a decrease in testis weight, lowered gonadosomatic index, suppressed sex hormone levels, and reduced mature sperm count. Further exploration revealed that the expression of sex hormone synthesis-related genes, including star, cyp19a1a, and hsd11b2, was significantly affected (p < 0.05), which may be an important reason for the decrease in sex hormone synthesis and consequent inhibition of testicular development. At the same time, the fertilization ability of mature sperm in both treatment groups significantly decreased. Scanning electron microscopy and fluorescence polarization tests showed that reducing cholesterol levels significantly increased the rate of sperm head cell membrane damage, while both increasing and decreasing cholesterol levels led to a reduction in sperm cell membrane fluidity, which may be the main reason for the decrease in sperm fertilization ability. This study demonstrates that both increasing and decreasing the levels of cholesterol are detrimental to the fish spermatogenesis, providing fundamental information for the study of fish reproduction and also a reference for the causes of male reproductive dysfunction.

Effects of 17α-ethinylestradiol on the neuroendocrine gonadotropic system and behavior of European sea bass larvae (Dicentrarchus labrax)

The widespread use of 17α-ethinylestradiol (EE2), and other estrogenic endocrine disruptors, results in a continuous release of estrogenic compounds into aquatic environments. Xenoestrogens may interfere with the neuroendocrine system of aquatic organisms and may produce various adverse effects. The aim of the present study was to expose European sea bass larvae (Dicentrarchus labrax) to EE2 (0.5 and 50 nM) for 8 d and determine the expression levels of brain aromatase (cyp19a1b), gonadotropin-releasing hormones (gnrh1, gnrh2, gnrh3), kisspeptins (kiss1, kiss2) and estrogen receptors (esr1, esr2a, esr2b, gpera, gperb). Growth and behavior of larvae as evidenced by locomotor activity and anxiety-like behaviors were measured 8 d after EE2 treatment and a depuration period of 20 d. Exposure to 0.5 nM EE2 induced a significant increase in cyp19a1b expression levels, while upregulation of gnrh2, kiss1, and cyp19a1b expression was noted after 8 d at 50 nM EE2. Standard length at the end of the exposure phase was significantly lower in larvae exposed to 50 nM EE2 than in control; however, this effect was no longer observed after the depuration phase. The upregulation of gnrh2, kiss1, and cyp19a1b expression levels was found in conjunction with elevation in locomotor activity and anxiety-like behaviors in larvae. Behavioral alterations were still detected at the end of the depuration phase. Evidence indicates that the long-lasting effects of EE2 on behavior might impact normal development and subsequent fitness of exposed fish.

Verification of In Vivo Estrogenic Activity for Four Per- and Polyfluoroalkyl Substances (PFAS) Identified as Estrogen Receptor Agonists via New Approach Methodologies

Given concerns about potential toxicological hazards of the thousands of data-poor per- and polyfluorinated alkyl substances (PFAS) currently in commerce and detected in the environment, tiered testing strategies that employ high-throughput in vitro screening as an initial testing tier have been implemented. The present study evaluated the effectiveness of previous in vitro screening for identifying PFAS capable, or incapable, of inducing estrogenic responses in fish exposed in vivo. Fathead minnows (Pimephales promelas) were exposed for 96 h to five PFAS (perfluorooctanoic acid [PFOA]; 1H,1H,8H,8H-perfluorooctane-1,8-diol [FC8-diol]; 1H,1H,10H,10H-perfluorodecane-1,10-diol [FC10-diol]; 1H,1H,8H,8H-perfluoro-3,6-dioxaoctane-1,8-diol [FC8-DOD]; and perfluoro-2-methyl-3-oxahexanoic acid [HFPO-DA]) that showed varying levels of in vitro estrogenic potency. In agreement with in vitro screening results, exposure to FC8-diol, FC10-diol, and FC8-DOD caused concentration-dependent increases in the expression of transcript coding for vitellogenin and estrogen receptor alpha and reduced expression of insulin-like growth factor and apolipoprotein eb. Once differences in bioconcentration were accounted for, the rank order of potency in vivo matched that determined in vitro. These results provide a screening level benchmark for worst-case estimates of potential estrogenic hazards of PFAS and a basis for identifying structurally similar PFAS to scrutinize for putative estrogenic activity.

Exposure to an environmentally relevant concentration of 17α-ethinylestradiol disrupts craniofacial development of juvenile zebrafish

Endocrine disrupting chemicals (EDCs) can interact with native hormone receptors to interfere with and disrupt hormone signalling that is necessary for a broad range of developmental pathways. EDCs are pervasive in our environment, in particular in our waterways, making aquatic wildlife especially vulnerable to their effects. Many of these EDCs are able to bind to and activate oestrogen receptors, causing aberrant oestrogen signalling. Craniofacial development is an oestrogen-sensitive process, with oestrogen receptors expressed in chondrocytes during critical periods of development. Previous studies have demonstrated a negative effect of high concentrations of oestrogen on early craniofacial patterning in the aquatic model organism, the zebrafish (Danio rerio). In order to determine the impacts of exposure to an oestrogenic EDC, we exposed zebrafish larvae and juveniles to either a high concentration to replicate previous studies, or a low, environmentally relevant concentration of the oestrogenic contaminant, 17α-ethinylestradiol. The prolonged / chronic exposure regimen was used to replicate that seen by many animals in natural waterways. We observed changes to craniofacial morphology in all treatments, and most strikingly in the larvae-juveniles exposed to a low concentration of EE2. In the present study, we have demonstrated that the developmental stage at which exposure occurs can greatly impact phenotypic outcomes, and these results allow us to understand the widespread impact of oestrogenic endocrine disruptors. Given the conservation of key craniofacial development pathways across vertebrates, our model can further be applied in defining the risks of EDCs on mammalian organisms.

Anthropogenic impact on the reproductive health of two wild Patagonian fish species with differing reproductive strategies

A particularly concerning outcome of environmental pollution is the disturbance of reproductive processes. However, studies on the impacts of pollution on the reproductive health of fish inhabiting South American environments are limited. We studied the impact of anthropogenic pollution on the reproductive health of two sympatric Patagonian marine fish species with different reproductive strategies: the live-bearing rockfish Sebastes oculatus and the egg-laying Brazilian sandperch Pinguipes brasilianus. Our findings reveal that both species presented some degree of reproductive disturbance when inhabiting an affected site, but the specific alterations differed depending on the species, sex, and season. During the reproductive season, 17β-estradiol levels were elevated in females of both species living in polluted areas, while no differences in androgen levels were observed in either species or season. The gonadosomatic index (GSI) was affected in both sexes of S. oculatus during the non-reproductive season, while the gonadal stages were mainly affected in both sexes of P. brasilianus. No signs of intersex condition were observed. Our results highlight the importance of including diverse reproductive parameters to better understand anthropogenic effects on wild animals. Long-term studies including other fish species and including offspring (to evaluate possible transgenerational effects) will be necessary to determine the consequences of the documented reproductive alterations, particularly whether fish species inhabiting Patagonian marine reef areas will be able to reproductively adapt to increasing marine anthropogenic disturbances.

Comparative Effects of Embryonic Metformin Exposure on Wild and Laboratory-Spawned Fathead Minnow (Pimephales promelas) Populations

Metformin is routinely detected in aquatic ecosystems because of its widespread use as a treatment for Type 2 diabetes. Laboratory studies have shown that exposure to environmentally relevant concentrations of metformin can alter metabolic pathways and impact the growth of early life stage (ELS) fish; however, it is unknown whether these effects occur in wild populations. Herein, we evaluate whether findings from laboratory studies are representative and describe the relative sensitivities of both populations. Duplicate exposures (0, 5, or 50 μg/L metformin) were conducted using wild- and lab-spawned fathead minnow (Pimephales promelas) embryos. Apart from the water source, exposure conditions remained constant. Wild embryos were exposed to previously dosed lake water to account for changes in bioavailability, while reconstituted freshwater was used for the laboratory study. Developmental metformin exposure differentially impacted the growth and morphology of both cohorts, with energy dyshomeostasis and visual effects indicated. The fitness of wild-spawned larvae was impacted to a greater extent relative to lab-spawned fish. Moreover, baseline data reveal important morphological differences between wild- and lab-spawned ELS fatheads that may diminish representativeness of lab studies. Findings also confirm the bioavailability of metformin in naturally occurring systems and suggest current exposure scenarios may be sufficient to negatively impact developing fish.

Effects of Anthropic Pollutants Identified in Pampas Lakes on the Development and Reproduction of Pejerrey Fish Odontesthes bonariensis

Anthropic activities can seriously affect the health of the organisms inhabiting them, and the observation of any alteration in the reproduction of fish could be associated with the presence of endocrine disruptors. In this manuscript we have collected information on the adverse effects of pollutants (heavy metals, environmental steroids, and agrochemicals), present in Chascomús lake, Argentina, either at environmentally relevant and pharmacological concentrations on reproduction, embryonic development, and larval survival of pejerrey fish Odontesthes bonariensis. During development, it has been reported that 17β-estradiol (E₂) feminized and reduced larval survival, while 17α-ethinyl-estradiol (EE₂) not only feminized but also affected both embryo and larval survival. In adult male fish, treatments with EE₂ and E₂ + EE₂ were able to increase mRNA abundance of gnrh3 and cyp19a1b and decreased those of gonadotropin receptors (fshr and lhcgr). Heavy metals such as cadmium, chromium, and copper negatively affected sperm quality, diminishing the motility. Also, a decrease in the percentage of hatching rate and larval survival was also observed with the same metals, highlighting zinc as the most detrimental metal. Furthermore, all these metals altered the expression of hypothalamic and pituitary genes related to reproduction in male pejerrey (gnrh1,2,3; cyp19a1b; fshb; lhb; fshr and, lhcgr). Moreover, in all cases pyknotic cells, corresponding to the degeneration of the germ cells, were observed in the testes of exposed fish. For agrochemicals, exposure of male pejerrey to environmental concentrations of glyphosate did not cause alterations on the endocrine reproductive axis. However, male pejerrey with gonadal abnormalities such as the presence of intersex (testis-ova) gonads were found in other Pampa´s lakes with high concentrations of atrazine and glyphosate associated with soybean and corn crops near their coasts. These types of studies demonstrate that pejerrey, an endemic species with economic importance inhabiting the Pampas shallow lakes, can be used as a sentinel species. It should be noted that increased pollution of aquatic ecosystems and the effects on the reproduction of organisms can lead to a decline in fish populations worldwide. Which, added to overfishing and other external factors such as global warming, could cause an eventual extinction of an emblematic species.

Antidepressants as Endocrine Disrupting Compounds in Fish

As antidepressant usage by the global population continues to increase, their persistent detection in aquatic habitats from municipal wastewater effluent release has led to concerns of possible impacts on non-target organisms, including fish. These pharmaceuticals have been marketed as mood-altering drugs, specifically targeting the monoaminergic signaling in the brain of humans. However, the monoaminergic systems are highly conserved and involved in the modulation of a multitude of endocrine functions in vertebrates. While most studies exploring possible impact of antidepressants on fish have focused on behavioural perturbations, a smaller spotlight has been placed on the endocrine functions, especially related to reproduction, growth, and the stress response. The purpose of this review is to highlight the possible role of antidepressants as endocrine disruptors in fish. While studies linking the effects of environmentally relevant levels of antidepressant on the endocrine system in fish are sparse, the emerging evidence suggests that early-life exposure to these compounds have the potential to alter the developmental programming of the endocrine system, which could persist as long-term and multigenerational effects in teleosts.

The abundance of endocrine-disrupting chemicals (EDCs) in downstream of the Bengawan Solo and Brantas rivers located in Indonesia

Numerous chemical substances are used for daily life activities have an effect on the endocrine system and are frequently classed as endocrine-disrupting chemicals (EDCs). The present study investigated the fact and distribution of EDCs type (estrogen, plasticizer, and preservative). In particular, EDCs such as estriol, 1,2,4 triazole, 17α-ethinylestradiol, methyl paraben, estrone, 3,4,4 trichlorocarbanilide, 17β-estradiol, and bisphenol A (BPA) were selected as the target EDCs for the detection in the Bengawan Solo and Brantas rivers located in Indonesia. Among the targeted EDCs, BPA is found to be highest in the water samples of Bengawan Solo (1070 ng/L and mean at 219 ng/L) and Brantas (556 ng/L and mean at 222 ng/L) rivers. The EDCs concentration is higher in both rivers during the dry season compared to the wet season due to the dilution effect caused by heavy rainfall. The entry of municipal wastewater is the primary sources of EDCs contamination in both rivers. Finally, this study suggests that the contamination level of EDCs in river water could pose an environmental threat, particularly during dry seasons.

Polycarbonate plastic monomer (bisphenol-A) as emerging contaminant in Nigeria: Levels in selected rivers, sediments, well waters and dumpsites

Despite decades of research into the environmental fate and levels of the endocrine-disrupting polycarbonate Plastic monomer, bisphenol-A (BPA), data remain scarce from many developing countries. Here, occurrence and levels of BPA were investigated in water and sediments of three rivers, selected dumpsites and well waters in Ondo State, Southwestern Nigeria. The study also investigated the influence of matrix physicochemical characteristics on their BPA retention. BPA values ranged from 0.41-5.19 μg/L in river waters, 0.64-10.6 μg/kg in river sediments, 0.63-0.68 μg/L in well waters and 0.72-1.09 μg/kg in waste dumpsites. BPA concentrations in the river waters showed a strong association with chemical oxygen demand (COD) values. High BPA concentrations were also found associated with high chloride contents of drinking well waters. Detection in river and well waters revealed exposure routes of humans, cattle and aquatic species to BPA in the region.

Proximate causes and ultimate effects of common antidepressants, fluoxetine and venlafaxine, on fish behavior

Antidepressant (AD) drugs are widely prescribed for the treatment of psychiatric disorders, including depression and anxiety disorders. The continuous use of ADs causes significant quantities of these bioactive chemicals to enter the aquatic ecosystems mainly through wastewater effluent discharge. This may result in many aquatic organisms being inadvertently affected by these drugs. Fluoxetine (FLX) and venlafaxine (VEN) are currently among the most widely detected ADs in aquatic systems. A growing body of experimental evidence demonstrates that FLX and VEN have a substantial capacity to induce neurotoxicity and cause behavioral dysfunctions in a wide range of teleost species. At the same time, these studies often report seemingly contradictory results that are confounding in nature. Hence, we clearly require comprehensive reviews that attempt to find overarching patterns and establish possible causes for these variable results. This review aims to explore the current state of knowledge regarding the neurobehavioral effects of FLX and VEN on fishes. This study also discusses the potential mechanistic linkage between the neurotoxicity of ADs and behavioral dysfunction and identifies key knowledge gaps and areas for future research.

Do microplastics impair male dominance interactions in fish? A test of the vector hypothesis

Microplastics (MPs) are widespread in aquatic environments and have become a critical environmental issue in recent years due to their adverse impacts on the physiology, reproduction, and survival of aquatic animals. Exposure to MPs also has the potential to induce sub-lethal behavioral changes that can affect individual fitness, but these effects are understudied. Many plastic additives introduced during the manufacture of MPs are known endocrine-disrupting chemicals (EDCs) that mimic the action of natural hormones, alter sexual and competitive behavior, and impair reproductive success in fish. In addition, EDCs and other aquatic contaminants may adhere to MPs in the environment, the latter of which may serve as transport vectors for these compounds (i.e., the vector hypothesis). In this study, we staged territorial contests between control males, and males exposed to virgin MP particles or to MPs previously immersed in one of two environmentally relevant concentrations of 17-alpha ethinyl estradiol (EE2; 5 ng/L and 25 ng/L) to evaluate the independent and synergistic effects of exposure to MPs and a common environmental estrogen on male-male aggression and competitive territory acquisition in a freshwater fish, Pimephales promelas. Short-term (30 days) dietary exposure to MPs did not impair the ability of males to successfully compete for and obtain a breeding territory. Overall levels of aggression in control and exposed males were also similar across trial series. These results help to fill a critical knowledge gap regarding the direct and indirect (vector-borne) effects of MPs on the reproductive behavior of aquatic vertebrates in freshwater systems.

Analysis of Indirect Biomarkers of Effect after Exposure to Low Doses of Bisphenol A in a Study of Successive Generations of Mice

Simple Summary

Living beings are constantly and inadvertently exposed to a series of environmental and food pollutants, triggering effects on health that are transmitted over generations. Bisphenol A is a compound produced in large amounts world-wide and used in the manufacture of plastic containers and other utensils for daily use. It is an environmental and food pollutant with a demonstrated capacity to produce effects on the health of organisms exposed to it. The objective of our study was to identify possible indirect biomarkers of effect by means of the analysis of the blood biochemistry, and of certain reproductive parameters of animals exposed to Bisphenol A in doses considered to be safe over different generations. Our results did not show any modifications in the reproduction parameters evaluated, such as the duration of the estrous cycle, the size of the litters, or the percentage of the young alive at weaning time. However, they showed that there were alterations in biochemical parameters like glucose, total proteins, and albumin, which could therefore, be regarded as indirect indicators of an early effect of alterations in health caused by this compound.

Abstract

Bisphenol A (BPA) is considered as being an emerging pollutant, to which both animal and human populations are continuously and inadvertently exposed. The identification of indirect biomarkers of effect could be a key factor in determining early adverse outcomes from exposure to low doses of BPA. Thus, this study on mice aims to evaluate and identify indirect biomarkers of effect through the analysis of their blood biochemistry, and of certain reproduction parameters after exposure to different BPA concentrations (0.5, 2, 4, 50, and 100 µg/kg BW/day) in drinking water over generations. Our results showed that there were no modifications in the reproductive parameters evaluated, like estrous cycle duration, litter size, or the percentage of the young alive at reaching the weaning stage, at the exposure levels evaluated. However, there were modifications in the biochemical parameters, e.g., alterations in the glucose levels, that increased significantly (p < 0.05) in the breeders at the higher exposure doses (50 and 100 µg/kg BW/day in F1; 50 µg/kg BW/day in F2 and 100 µg/kg BW/day in F3), that would suggest that the BPA could induce hyperglycemia and its complications in adult animals, probably due to some damage in the pancreas cells; albumin, that increased in the breeders exposed to the highest dose in F1 and F3, inferring possible hepatic alterations. Further, total proteins showed a diminution in their values in F1 and F2, except the group exposed to 100 µg/kg BW/day, whereas in F3 the values of this parameter increased with respect to the control group, this aspect likely being related to a possible hepatic and renal alteration. Based on these results, glucose, albumin, and total proteins could initially be considered as early indicators of indirect effect after prolonged exposure to low BPA doses over generations.

Biological effect and chemical monitoring of Watch List substances in European surface waters: Steroidal estrogens and diclofenac - Effect-based methods for monitoring frameworks

Three steroidal estrogens, 17α-ethinylestradiol (EE2), 17β-estradiol (E2), estrone (E1), and the non-steroidal anti-inflammatory drug (NSAID), diclofenac have been included in the first Watch List of the Water Framework Directive (WFD, EU Directive 2000/60/EC, EU Implementing Decision 2015/495). This triggered the need for more EU-wide surface water monitoring data on these micropollutants, before they can be considered for inclusion in the list of priority substances regularly monitored in aquatic ecosystems. The revision of the priority substance list of the WFD offers the opportunity to incorporate more holistic bioanalytical approaches, such as effect-based monitoring, alongside single substance chemical monitoring. Effect-based methods (EBMs) are able to measure total biological activities (e.g., estrogenic activity or cyxlooxygenase [COX]-inhibition) of specific group of substances (such as estrogens and NSAIDs) in the aquatic environment at low concentrations (pg/L). This makes them potential tools for a cost-effective and ecotoxicologically comprehensive water quality assessment. In parallel, the use of such methods could build a bridge from chemical status assessments towards ecological status assessments by adressing mixture effects for relevant modes of action. Our study aimed to assess the suitability of implementing EBMs in the WFD, by conducting a large-scale sampling and analysis campaign of more than 70 surface waters across Europe. This resulted in the generation of high-quality chemical and effect-based monitoring data for the selected Watch List substances. Overall, water samples contained low estrogenicity (0.01-1.3 ng E2-Equivalent/L) and a range of COX-inhibition activity similar to previously reported levels (12-1600 ng Diclofenac-Equivalent/L). Comparison between effect-based and conventional analytical chemical methods showed that the chemical analytical approach for steroidal estrogens resulted in more (76%) non-quantifiable data, i.e., concentrations were below detection limits, compared to the EBMs (28%). These results demonstrate the excellent and sensitive screening capability of EBMs.

Mechanistic revealing of reproductive behavior impairment in male guppy (Poecilia reticulata) induced by environmentally realistic 2,2'-dithiobis-pyridine exposure

Although (PS)₂, the primary degradation product of emerging antifouling biocides metal pyrithiones (MePTs), can disrupt the reproductive behavior of fish at an environmentally relevant ng/L level, the underlying mechanism is still largely unknown. This study exposed sexually mature male guppy (Poecilia reticulata) to 20, 200, and 2000 ng/L (PS)₂ to explore the compromised effect of (PS)₂ on reproductive behavior through a realistic competing scenario. The results showed that (PS)₂ suppressed male guppies' sexual interest to stimulus females, reduced their competitive behavior frequencies toward rival males, and decreased their mating time and frequency. (PS)₂ exposure did not affect male guppies' secondary sexual characteristics or induce estrogenic activity. Whole-brain transcriptome sequencing identified 1070 differentially expressed genes (DEGs) with 872 up-regulated genes, which were functionally enriched into Gene Ontology terms pertaining to extracellular matrix (ECM) and extracellular region. KEGG enrichment for the DEGs uncovered that the activations of ECM-receptor interaction and focal adhesion pathways could be the underlying molecular mechanism implicated in the (PS)₂ induced reproductive behavior impairment. This work would deliver a substantial contribution to the understanding of the ecological safety of MePTs biocides.

A review on recent trends in the removal of emerging contaminants from aquatic environment using low-cost adsorbents

Emerging contaminants (ECs), a class of contaminants with low concentrations but significant harm, have received a lot of attention in recent times. ECs comprises of various chemicals that enter the environment every day. In today's modern lifestyle, we use many chemical-based products. These persist in wastewater and ultimately enter the water bodies, causing serious problems to the human and aquatic ecosystem. This is because the conventional wastewater treatment methods are inefficient in identifying and removing such contaminants. Aiming for a long-term, effective solution to this issue, Adsorption was proposed. Although several adsorbents are already present in the market, which have proved beneficial in removing such ECs, not all are affordable. This article reviews replacing costly adsorbents with agriculture-based biomass that are abundant, inexpensive, and biodegradable and possess excellent adsorption capacity. The objectives of this article is to look at adsorption as a viable treatment option for emerging pollutants, as well as sophisticated and cost-effective emerging contaminants treatment options.

Estrogens regulate early embryonic development of the olfactory sensory system via estrogen-responsive glia

Estrogens are well-known to regulate development of sexual dimorphism of the brain; however, their role in embryonic brain development prior to sex-differentiation is unclear. Using estrogen biosensor zebrafish models, we found that estrogen activity in the embryonic brain occurs from early neurogenesis specifically in a type of glia in the olfactory bulb (OB), which we name estrogen-responsive olfactory bulb (EROB) cells. In response to estrogen, EROB cells overlay the outermost layer of the OB and interact tightly with olfactory sensory neurons at the olfactory glomeruli. Inhibiting estrogen activity using an estrogen receptor antagonist, ICI182,780 (ICI), and/or EROB cell ablation impedes olfactory glomerular development, including the topological organisation of olfactory glomeruli and inhibitory synaptogenesis in the OB. Furthermore, activation of estrogen signalling inhibits both intrinsic and olfaction-dependent neuronal activity in the OB, whereas ICI or EROB cell ablation results in the opposite effect on neuronal excitability. Altering the estrogen signalling disrupts olfaction-mediated behaviour in later larval stage. We propose that estrogens act on glia to regulate development of OB circuits, thereby modulating the local excitability in the OB and olfaction-mediated behaviour.

Prediction of adverse effects of effluents containing phenolic compounds in the Ba River on the ovary of fish (Hemiculter leucisculus) using transcriptomic and metabolomic analyses

The aim of this work was to evaluate the endocrine disrupting effects on the ovarian development of sharpbelly (Hemiculter leucisculus) caused by effluents containing phenolic compounds. This was achieved using integrated transcriptomic and metabolomic analyses, along with histopathological examinations. Sharpbelly, an indigenous freshwater fish widely distributed in East Asia, were collected by pole fishing from three sampling sites in the Ba River. These sampling sites include a mid-stream site near a wastewater outfall and a reference site located upstream and a far field comparison site located downstream. In sharpbelly collected near the wastewater discharge, the oocyte development was activated, compared to the other two sites. Histopathological alterations in the fish ovaries were likely due to the upregulated steroid hormone biosynthesis process, as suggested by the differentially expressed genes (e.g., hsd3b, hsd17b1) and differentially accumulated metabolites (e.g., pregnenolone). Additionally, under the stress of effluents containing phenolic compounds, genes related to the signaling pathways for oxidative phosphorylation and leukocyte transendothelial migration were dysregulated, suggesting the potential induction of inflammation and several ovarian diseases. Overall, these findings suggest that effluents containing phenolic compounds influence ovary development and reproductive function of female sharpbelly. Whether there is any resulting dysfunction of folliculogenesis, abnormality of ovulation, production of premature eggs and/or potential induction of ovarian cancers remains to be determined by further studies, for a better evaluation on effluents containing phenolic compounds to the fish fertility and the health of their offspring, and even the stability of the wild fish population. Notably, the integration of transcriptomics and metabolomics can complement the routine chemical analysis to comprehensively monitor the effects of wastewater treatment plant effluents on the health of wild fish.

Social status modulates the behavioral and physiological consequences of a chemical pollutant in animal groups

The social environment (i.e., the suite of social interactions that occur among individuals that can result in variation in social ranks) is a commonly overlooked aspect of biology when scientists evaluate the effects of chemical contaminants. The social environment, however, represents the arena in which individual-level performance shapes group- or population-level outcomes and may therefore mediate many of the ultimate consequences of chemicals for wildlife. Here, we evaluated the role that the social environment plays in determining the consequences of pollutant exposure. We exposed groups of juvenile brown trout (Salmo trutta) to an emerging pharmaceutical pollutant that is commonly detected in freshwaters (the benzodiazepine, oxazepam) and allowed them to form dominance hierarchies. Exposure affected dominant and subordinate fish differently, causing fish to become less aggressive at high doses and subordinate fish to become more competitively successful at low doses. These perturbations had further consequences for growth, fin damage, and survival. Exposure also modulated physiological stress in the hierarchy, and social status itself affected how much oxazepam was absorbed in tissues, potentially creating a dynamic feedback loop that further influences the asymmetric effects of exposure on differing social statuses. Many effects followed a "U-shaped" dose-response curve, highlighting the importance of nonlinear, low-dose effects. Altogether, we show that social structure in animal groups can interact with and modulate the effects of an environmental contaminant. We underscore the need to account for an organism's natural ecological context, including their social environment, in future experiments and environmental risk assessments to predict the effects of chemical contaminants on wildlife.

Ingestion of microplastics and its potential for causing structural alterations and oxidative stress in Indian green mussel Perna viridis- A multiple biomarker approach

The present study has investigated the distribution of microplastics in sediment and its impact on histological, ultrastructural, and oxidative stress mechanisms in Perna viridis (P. viridis) from Kasimedu, Chennai, India. The results confirmed that fibers were the predominant type of microplastics observed, followed by spheres, flakes, sheets, and fragments. The observed microplastics were confirmed as polyester, polypropylene, polyethylene, cellophane, and rayon using μ-FT-IR. Microplastic particles entangled in gills caused abrasion of ciliated structure and hemocyte infiltration in the hemolymph vessels. The digestive gland showed a shrunken nucleus, dark inclusions, and damage in the nucleoid core structure. Enlarged vacuoles and the presence of clusters of vesicles presumably represented the transformed golgi cisternae. Further, the results confirmed that oxidative stress markers were significantly high in gills and digestive diverticula of P. viridis. Overall, the results indicated that microplastics induced different toxic physiological and structural alterations in gills and digestive diverticula of P. viridis. These findings highlighted the necessity to focus on exposure studies to understand the absolute magnitude of the problem due to microplastic pollution in the urban estuarine ecosystems of Chennai, Tamil Nadu, India.

Impact of bisphenol-A and synthetic estradiol on brain, behavior, gonads and sex hormones in a sexually labile coral reef fish

Endocrine disrupting chemicals, such as bisphenol A (BPA) and ethinylestradiol (EE2), are detected in the marine environment from plastic waste and wastewater effluent. However, their impact on reproduction in sexually labile coral reef fish is unknown. The objective of this study was to determine impacts of environmentally relevant concentrations of BPA and EE2 on behavior, brain gene expression, gonadal histology, sex hormone profile, and plasma vitellogenin (Vtg) levels in the anemonefish, Amphiprion ocellaris. A. ocellaris display post-maturational sex change from male to female in nature. Sexually immature, male fish were paired together and fed twice daily with normal food (control), food containing BPA (100 μg/kg), or EE2 (0.02 μg/kg) (n = 9 pairs/group). Aggression toward an intruder male was measured at 1, 3, and 6 months. Blood was collected at 3 and 6 months to measure estradiol (E2), 11-ketotestosterone (11-KT), and Vtg. At the end of the study, fish were euthanized to assess gonad morphology and to measure expression of known sexually dimorphic genes in the brain. Relative to control, BPA decreased aggression, altered brain transcript levels, increased non-vitellogenic and vitellogenic eggs in the gonad, reduced 11-KT, and increased plasma Vtg. In two BPA-treated pairs, both individuals had vitellogenic eggs, which does not naturally occur. EE2 reduced 11-KT in subordinate individuals and altered expression of one transcript in the brain toward the female profile. Results suggest BPA, and to a lesser extent EE2, pollution in coral reef ecosystems could interfere with normal reproductive physiology and behavior of the iconic sexually labile anemonefish.

Suspended solids-associated toxicity of hydraulic fracturing flowback and produced water on early life stages of zebrafish (Danio rerio)

Hydraulic fracturing flowback and produced water (HF-FPW), which contains polyaromatic hydrocarbons (PAHs) and numerous other potential contaminants, is a complex wastewater produced during the recovery of tight hydrocarbon resources. Previous studies on HF-FPW have demonstrated various toxicological responses of aquatic organisms as consequences of combined exposure to high salinity, dissolved organic compounds and particle/suspended solids-bound pollutants. Noteworthy is the lack of studies illustrating the potentially toxic effects of the FPW suspended solids (FPW-SS). In this study, we investigated the acute and sublethal toxicity of suspended solids filtered from six authentic FPW sample collected from two fracturing wells, using a sediment contact assay based on early-life stages of zebrafish (Danio rerio). PAHs profiles and acute toxicity tests provided initial information on the toxic potency of the six samples. Upon exposure to sediment mixture at two selected doses (1.6 and 3.1 mg/mL), results showed adverse effects in larval zebrafish, as revealed by increased Ethoxyresorufin-O-deethylase (EROD) activity. Transcriptional alterations were also observed in xenobiotic biotransformation (ahr, pxr, cyp1a, cyp1b1, cyp1c1, cyp1c2, cyp3a65, udpgt1a1, udpgt5g1), antioxidant response (sod1, sod2, gpx1a, gpx1b) and hormone receptor signaling (esr1, esr2a, cyp19a1a, vtg1) genes. The results demonstrated that even separated from the complex aqueous FPW mixture, FPW-SS can induce toxicological responses in aquatic organisms' early life stages. Since FPW-SS could sediment to the bottom of natural wetland acting as a continuous source of contaminants, the current findings imply the likelihood of long-term environmental risks of polluted sediments on aquatic ecosystems due to FPW spills.

Behavioral and reproductive effects in Poecilia vivipara males from a tropical estuary affected by estrogenic contaminants

Contamination of aquatic habitats by endocrine disruptor chemicals is a major concern globally. This study evaluated histochemical, behavioral, and reproductive effects on adult male Poecilia vivipara sampled from Capibaribe River Estuarine System (CRES), compared to laboratory control males after breeding with virgin control females. CRES is contaminated by a mixture of estrogenic contaminants estrone, 17β-estradiol, estriol, 17α-Ethinylestradiol, bisphenol A and caffeine in concentrations averaging 13.9; 4.2; 19.5; 8.6; 27 and 23.2 ng L^-1, respectively. Estrogenic risk in 17β-estradiol-equivalent-concentrations is above probable no effect concentrations. Males sampled from CRES indicated liver phosphoprotein induction, decreased number of contacts and copulation attempts when paired with control females, slower swimming speed and lower female impregnation success rates, compared to control males. A reduction of 62% in fecundity was observed in control females paired with field sampled males compared with control males. Our results highlight hazards posed to fish reproduction by estrogenic micropollutants.

Effects of Wastewater Treatment Plant Effluent in a Receiving Stream on Reproductive Behavior of Fathead Minnows (Pimephales promelas)

Wastewater treatment plant effluents contain a variety of endocrine disrupting chemicals (EDCs), including chemicals with estrogenic activity such as 17β-estradiol (E2), 17α-ethinyl estradiol (EE2), and nonylphenols. These substances can affect both behavior and physiology in vertebrate animals. To explore the presence and effects of these EDCs in a natural setting, juvenile and adult male fathead minnows, Pimephales promelas, were held in cages upstream and downstream of the effluent site of a wastewater treatment plant for 21 days and subsequently tested for changes in reproductive behaviors and production of vitellogenin. Additionally, estrogenic activity in the stream was measured using a yeast bioassay. Estrogenicity was found to be significantly higher downstream of the wastewater effluent when compared to levels upstream. Vitellogenin levels did not show a correlational pattern with levels of estrogenicity in the water, but two measures of reproductive behaviors occurred significantly less often in downstream males than upstream males. This suggests that a brief (three-week) exposure to stream water containing wastewater treatment plant effluent can bring about changes in reproductive behavior of fish and that behavior may be more sensitive to low levels of environmental endocrine disruptors than vitellogenin production.

Zebrafish Optomotor Response and Morphology Are Altered by Transient, Developmental Exposure to Bisphenol-A

Estrogen-specific endocrine disrupting compounds (EDCs) are potent modulators of neural and visual development and common environmental contaminants. Using zebrafish, we examined the long-term impact of abnormal estrogenic signaling by testing the effects of acute, early exposure to bisphenol-A (BPA), a weak estrogen agonist, on later visually guided behaviors. Zebrafish aged 24 h postfertilization (hpf), 72 hpf, and 7 days postfertilization (dpf) were exposed to 0.001 μM or 0.1 μM BPA for 24 h, and then allowed to recover for 1 or 2 weeks. Morphology and optomotor responses (OMRs) were assessed after 1 and 2 weeks of recovery for 24 hpf and 72 hpf exposure groups; 7 dpf exposure groups were additionally assessed immediately after exposure. Increased notochord length was seen in 0.001 μM exposed larvae and decreased in 0.1 μM exposed larvae across all age groups. Positive OMR was significantly increased at 1 and 2 weeks post-exposure in larvae exposed to 0.1 μM BPA when they were 72 hpf or 7 dpf, while positive OMR was increased after 2 weeks of recovery in larvae exposed to 0.001 μM BPA at 72 hpf. A time-delayed increase in eye diameter occurred in both BPA treatment groups at 72 hpf exposure; while a transient increase occurred in 7 dpf larvae exposed to 0.1 μM BPA. Overall, short-term developmental exposure to environmentally relevant BPA levels caused concentration- and age-dependent effects on zebrafish visual anatomy and function.

Exposure to permethrin or chlorpyrifos causes differential dose- and time-dependent behavioral effects at early larval stages of an endangered teleost species

Pyrethroid and organophosphate pesticides are two of the most commonly used classes of insecticide worldwide. At sublethal concentrations, permethrin (a pyrethroid) and chlorpyrifos (an organophosphate) impact behavior in model fish species. We investigated behavioral effects of environmentally relevant concentrations of permethrin or chlorpyrifos on early larval delta smelt Hypomesus transpacificus, a Critically Endangered teleost species endemic to the San Francisco Bay Delta, California, USA. Using a photomotor behavioral assay of oscillating light and dark periods, we measured distance moved, turn angle, meander, angular velocity, rotations, thigmotaxis (time spent in the border versus center), and swim speed duration and frequency. The lowest concentrations of permethrin used in the tests (0.05 and 0.5 μg l⁻¹) caused significant increases in distance moved at 72 and 96 h, respectively. At 48, 72, and 96 h of exposure, 5 μg l⁻¹ of permethrin caused a hyperactive state in which the larvae significantly decreased thigmotaxis, quickly turning in short bouts of activity, characterized by significant increases in rotations and freezing events. Larvae exposed to 0.05 μg l⁻¹ chlorpyrifos significantly increased thigmotaxis at 72 and 96 h. In response to 5 μg l⁻¹ chlorpyrifos, larvae significantly increased velocity at 72 h exposure, and significantly increased freezing events at 96 h. Behavioral data on larval delta smelt exposed to contaminants present in their limited habitat have the potential to aid evaluations of the suitability of spawning and rearing habitats for this endangered species, thus improving conservation management strategies focused on this sensitive life stage.

Endocrine-Disrupting Compounds in Fish Physiology, with Emphasis on their Effects on the Arginine Vasotocin/Isotocin System

The purposes of this review are to promote better use of existing knowledge of marine pollutants especially endocrine-disrupting compounds (EDCs) and to draw attention to the slow progression of the research on the influence of those compounds on arginine vasotocin/isotocin system (AVT/IT) in fish. EDCs are leading to the degradation of fish habitats, reducing their spawning potential and possibly their population parameters (e.g. growth, maturation), by preventing fish from breeding and rebuilding their populations. Therefore, searching for new welfare indicators such as AVT and IT and developing research procedures mimicking environmental conditions using a versatile fish model is extremely important. Fish species such as Zebrafish (Daniorerio) and round goby (Neogobiusmelanostomus) can be recommended as very suitable modelsfor studying estrogenic EDCs on the AVT/IT system and other hormones involved in the neuroendocrine regulation of physiological processes in fish.These studies would not only improve our understanding of the effects of EDCs on vertebrates but could also help safeguard the well-being of aquatic and terrestrial organisms from the harmful effects of these compounds.

Transcriptome-wide changes associated with the reproductive behaviour of male guppies exposed to 17α-ethinyl estradiol

Although many pharmaceutical compounds (and their metabolites) can induce harmful impacts at the molecular, physiological and behavioural levels, their underlying mechanistic associations have remained largely unexplored. Here, we utilized RNA-Seq to build a whole brain transcriptome profile to examine the impact of a common endocrine disrupting pharmaceutical (17α-ethinyl estradiol, EE2) on reproductive behaviour in wild guppies (Poecilia reticulata). Specifically, we annotated 16,791 coding transcripts in whole brain tissue in relation to the courtship behaviour (i.e. sigmoid display) of EE2 exposed (at environmentally relevant concentration of 8 ng/L for 28-days) and unexposed guppies. Further, we obtained 10,960 assembled transcripts matching in the non-coding orthologous genomes. Behavioural responses were assessed using a standard mate choice experiment, which allowed us to disentangle chemical cues from visual cues. We found that a high proportion of the RNAseq reads aligned back to our de novo assembled transcriptome with 80.59% mapping rate. Behavioural experiments showed that when males were presented only with female visual cues, there was a significant interaction between male treatment and female treatment in the time spent in the preference zone. This is one of the first studies to show that transcriptome-wide changes are associated with the reproductive behaviour of fish: EE2 exposed male guppies that performed high levels of courtship had a gene profile that deviated the most from the other treatment groups, while both non-courting EE2 and control males had similar gene signatures. Using Gene Ontology pathway analysis, our study shows that EE2-exposed males had gene transcripts enriched for pathways associated with altered immunity, starvation, altered metabolism and spermatogenesis. Our study demonstrates that multiple gene networks orchestrate courting behaviour, emphasizing the importance of investigating impacts of pharmaceuticals on gene networks instead of single genes.

Bioaccumulation and reproductive toxicity of bisphenol A in male-pregnant seahorse (Hippocampus erectus) at environmentally relevant concentrations

Seahorses, with brood pouch in adult males, are a bioindicator species that exhibit specialized reproductive strategy of "male pregnancy". Bisphenol A (BPA), one of the most pervasive endocrine-disrupting chemicals (EDCs), is hazardous for reproductive, immune, and neurological systems. However, no evidence of BPA toxicity to the male-pregnant animals is available. Herein, the reproductive toxicity of BPA was evaluated in lined seahorses (Hippocampus erectus) following exposure to environmentally relevant concentrations (10, 100, and 1000 μg/L) through physiological, histological, and transcriptional analyses. Our results indicated BPA bioaccumulation to be positively correlated with exposure doses in both sexes. Ovarian failure was only observed in the high-dose BPA treatment group, accompanied by the apoptosis of follicular cells and up-regulation of pro-apoptotic genes. However, brood pouches maintenance were surprisingly inhibited at low concentration, and transcriptomic analysis revealed disturbed profiles of genes involved in the extracellular matrix and cell-cell adhesion pathways. Interestingly, seahorse testes were less sensitive to BPA exposure than that in other teleosts. Thus, our study suggests that BPA at environmentally relevant concentrations might cause reproductive dysfunction in seahorses, potentially exerting adverse effects on the seahorse population since most of them inhabit shallow coastal areas with prevalent estrogenic contaminants.

Cross-species physiological interactions of endocrine disrupting chemicals with the circadian clock

Endocrine disrupting chemicals (EDCs) are endocrine-active chemical pollutants that disrupt reproductive, neuroendocrine, cardiovascular and metabolic health across species. The circadian clock is a transcriptional oscillator responsible for entraining 24-hour rhythms of physiology, behavior and metabolism. Extensive bidirectional cross talk exists between circadian and endocrine systems and circadian rhythmicity is present at all levels of endocrine control, from synthesis and release of hormones, to sensitivity of target tissues to hormone action. In mammals, a range of hormones directly alter clock gene expression and circadian physiology via nuclear receptor (NR) binding and subsequent genomic action, modulating physiological processes such as nutrient and energy metabolism, stress response, reproductive physiology and circadian behavioral rhythms. The potential for EDCs to perturb circadian clocks or circadian-driven physiology is not well characterized. For this reason, we explore evidence for parallel endocrine and circadian disruption following EDC exposure across species. In the reviewed studies, EDCs dysregulated core clock and circadian rhythm network gene expression in brain and peripheral organs, and altered circadian reproductive, behavioral and metabolic rhythms. Circadian impacts occurred in parallel to endocrine and metabolic alterations such as impaired fertility and dysregulated metabolic and energetic homeostasis. Further research is warranted to understand the nature of interaction between circadian and endocrine systems in mediating physiological effects of EDC exposure at environmental levels.

Fish reproductive biology - Reflecting on five decades of fundamental and translational research

Driven by the broad diversity of species and physiologies and by reproduction-related bottlenecks in aquaculture, the field of fish reproductive biology has rapidly grown over the last five decades. This review provides my perspective on the field during this period, integrating fundamental and applied developments and milestones. Our basic understanding of the brain-pituitary-gonadal axis led to overcoming the failure of farmed fish to ovulate and spawn in captivity, allowing us to close the fish life cycle and establish a predictable, year-round production of eggs. Dissecting the molecular and hormonal mechanisms associated with sex determination and differentiation drove technologies for producing better performing mono-sex and reproductively-sterile fish. The growing contingent of passionate fish biologists, together with the availability of innovative platforms such as transgenesis and gene editing, as well as new models such as the zebrafish and medaka, have generated many discoveries, also leading to new insights of reproductive biology in higher vertebrates including humans. Consequently, fish have now been widely accepted as vertebrate reproductive models. Perhaps the best testament of the progress in our discipline is demonstrated at the International Symposia on Reproductive Physiology of Fish (ISRPF), at which our scientific family has convened every four years since the grandfather of the field, the late Ronald Billard, organized the inaugural 1977 meeting in Paimpont, France. As the one person who has been fortunate enough to attend all of these meetings since their inception, I have witnessed first-hand the astounding evolution of our field as we capitalized on the molecular and biotechnological revolutions in the life sciences, which enabled us to provide a higher resolution of fish reproductive and endocrine processes, answer more questions, and dive into deeper comprehension. Undoubtedly, the next (five) decades will be similarly exciting as we continue to integrate physiology with genomics, basic and translational research, and the small fish models with the aquacultured species.

Perfluorooctane sulfonate exposure alters sexual behaviors and transcriptions of genes in hypothalamic-pituitary-gonadal-liver axis of male zebrafish (Danio rerio)

BACKGROUND

Perfluorooctane sulfonate (PFOS) has been reported to be widely distributed in the environment and wildlife with persistence. PFOS has various biological toxicity, especially disturbing the endocrine system. However, few studies have systematically evaluated its effect on sexual behaviors alteration and reproduction-related genes. This study was performed to assess the effect of PFOS exposure on sexual behaviors and genes in hypothalamic-pituitary-gonadal-liver (HPGL) axis in adult zebrafish.

METHODS

Male adult zebrafish were exposed to PFOS (0, 2, 20, and 200 μg/L) and 5 μg/L estradiol (E₂) continuously for 21 days. Sexual behaviors were analyzed by zebrafish behavior tracking system and the mRNA levels of HPGL-related genes was detected by RT-qPCR.

RESULTS

Body weight of the fish was increased in 2, 200 μg/L PFOS and E₂ groups, and body length was increased with exposure to 2 μg/L PFOS and E₂. The hepatic-somatic index was decreased significantly after 2 and 20 μg/L PFOS treatments. Highest PFOS (200 μg/L) and E₂ exposure impaired standard zebrafish sexual behaviors significantly such as chasing, nose-tail and tail-touching. In brains, the genes gonadotropin-releasing hormone (GnRH), gonadotropin-releasing hormone receptor (GnRHr) were down-regulated with exposure to PFOS with linear trend and E₂ exposure, and follicle-stimulating hormone and luteinizing hormone were also down-regulated with exposure to 20 and 200 μg/L PFOS. In livers, the genes vitellogenin 1 and 3 were upregulated with some concentrations of PFOS and E₂, but estrogenic receptor α, β2 were upregulated in any concentration of PFOS and E₂. In testes, the expressions of follicle-stimulating hormone receptor, luteinizing hormone receptor, and androgen receptor genes were all significantly down-regulated with any exposure concentration of PFOS and E₂.

CONCLUSIONS

PFOS may alter the zebrafish reproductive system by disrupting endocrine activity and impairing sexual behaviors.

Effects of 17α-ethinylestradiol on sex ratio, gonadal histology and perianal hyperpigmentation of Cnesterodon decemmaculatus (Pisces, Poeciliidae) during a full-lifecycle exposure

The effects of 17α-ethinylestradiol (EE₂) on sex ratio, gonopodium morphology, and gonadal histology of C. decemmaculatus were assessed by a full-lifecycle exposure experiment. Newborn fish were waterborne exposed to 30, 100, and 300 ng EE₂/L for 90 d, using 50 fish per treatment. Additionally, in December of 2016, a field survey was conducted on a C. decemmaculatus population inhabiting the Girado Creek downstream of the Chascomus city wastewater effluent discharge. After 90 d of exposure, EE₂ was able to histologically skew the sex ratio toward females and inhibit the full gonopodium development since the lowest tested concentration (LOEC = 30 ng/L). At higher concentrations, EE₂ was toxic, inducing mortality in a concentration-dependent fashion (90 d-LC₅₀ = 109.9 ng/L) and altering the gonadal histoarchitecture, causing neither testes nor ovaries discernible histologically (LOEC = 100 ng/L). In addition, a novel response, perianal hyperpigmentation, was discovered been induced by the EE₂ exposure in a concentration-dependent fashion (90 d-EC₅₀ = 39.3 ng/L). A higher proportion of females and perianal hyperpigmentation were observed in wild fish collected from the Girado Creek. The major reached conclusions are: i) EE₂ induce different effects on the sexual traits of C. decemmaculatus when exposed from early-life or adult stages. ii) The most sensitive effects observed in the laboratory occur in a creek receiving wastewater effluent. iii) The perianal hyperpigmentation comes-up as a promising biomarker of exposure to estrogenic compounds.

Impact of rainfall on the occurrence, spatiotemporal distribution, and partition trend of micropollutants in Taihu Lake, China: Bisphenol A and 4-nonylphenol as examples

Very limited studies have evaluated the impact of rainfall on the fate of endocrine-disrupting micropollutants in lacustrine systems. This yearlong study investigated monthly fluctuation of bisphenol A (BPA) and 4-nonylphenol (NP) concentrations in both water and sediment samples from Taihu Lake and evaluated the impact of rainfall on their spatiotemporal distribution and partition trends. Results showed that BPA concentration in water was negatively correlated to rainfall while NP concentrations in both phases were positively related to rainfall. The spatial distribution of NP in the lake water was season specific with the lakeshore area higher than the central area during the wet season and a reversed pattern during the dry season. The spatial distributions of sediment-associated NP and BPA in both phases were not significantly different among seasons. Contrary partition tendencies were observed for BPA and NP that BPA tended to desorb from sediment and NP tended to be adsorbed during the wet season while the trends were reversed during the dry season. This study suggests that rainfall could affect the occurrence, distribution and environmental fate of micropollutants and should be considered in the monitoring program and risk assessment.

First observations of intersex development in paddlefish Polyodon spathula

This study reports the first cases of intersex (abnormal development of both male and female reproductive tissues in a gonad) paddlefish Polyodon spathula, an Acipenseriform species of large rivers in the central U.S. and in aquaculture worldwide. Despite a large, multi-decadal data set in Oklahoma, Montana, and North Dakota, intersex development was not observed until 2019, when two individuals were harvested from the Grand Lake/Neosho River stock in Oklahoma. This suggests that intersex development in mid-water, zooplanktivorous paddlefish is rarer than in bottom-dwelling sturgeons for which intersex development is regularly observed. Although contaminants are implicated in causing intersex development in other Acipenseriformes, more investigation is needed.

Applying a mechanistic model to predict interacting effects of chemical exposure and food availability on fish populations

The potential environmental impacts of chemical exposures on wildlife are of growing concern. Freshwater ecosystems are vulnerable to chemical effects and wildlife populations, including fish, can be exposed to concentrations known to cause adverse effects at the individual level. Wild fish populations are also often subjected to numerous other stressors simultaneously which in temperate climates often include sustained periods of food limitation. The potential interactive effects of chemical exposures and food limitation on fish populations are however difficult to establish in the field. Mechanistic modelling approaches can be employed to help predict how the physiological effects of chemicals and food limitation on individuals may translate to population-level effects. Here an energy budget-individual-based model was developed and the control (no chemical) model was validated for the three-spined stickleback. Findings from two endocrine active chemical (EAC) case studies, (ethinyloestradiol and trenbolone) were then used to investigate how effects on individual fecundity translated into predicted population-level effects for environmentally relevant exposures. The cumulative effects of chemical exposure and food limitation were included in these analyses. Results show that effects of each EAC on the population were dependent on energy availability, and effects on population abundance were exacerbated by food limitation. Findings suggest that chemical effects and density dependent food competition interact to determine population responses to chemical exposures. Our study illustrates how mechanistic modelling approaches might usefully be applied to account for specific chemical effects, energy budgets and density-dependent competition, to provide a more integrated evaluation of population outcomes in chemical risk assessments.

Paternal exposure to a common herbicide alters the behavior and serotonergic system of zebrafish offspring

Increasingly, studies are revealing that endocrine disrupting chemicals (EDCs) can alter animal behavior. Early life exposure to EDCs may permanently alter phenotypes through to adulthood. In addition, the effects of EDCs may not be isolated to a single generation − offspring may indirectly be impacted, via non-genetic processes. Here, we analyzed the effects of paternal atrazine exposure on behavioral traits (distance moved, exploration, bottom-dwelling time, latency to enter the top zone, and interaction with a mirror) and whole-brain mRNA of genes involved in the serotonergic system regulation (slc6a4a, slc6a4b, htr1Aa, htr1B, htr2B) of zebrafish (Danio rerio). F0 male zebraFIsh were exposed to atrazine at 0.3, 3 or 30 part per billion (ppb) during early juvenile development, the behavior of F1 progeny was tested at adulthood, and the effect of 0.3 ppb atrazine treatment on mRNA transcription was quantified. Paternal exposure to atrazine significantly reduced interactions with a mirror (a proxy for aggression) and altered the latency to enter the top zone of a tank in unexposed F1 offspring. Bottom-dwelling time (a proxy for anxiety) also appeared to be somewhat affected, and activity (distance moved) was reduced in the context of aggression. slc6a4a and htr1Aa mRNA transcript levels were found to correlate positively with anxiety levels in controls, but we found that this relationship was disrupted in the 0.3 ppb atrazine treatment group. Overall, paternal atrazine exposure resulted in alterations across a variety of behavioral traits and showed signs of serotonergic system dysregulation, demonstrating intergenerational effects. Further research is needed to explore transgenerational effects on behavior and possible mechanisms underpinning behavioral effects.

Temperature and Estrogen Alter Predator-Prey Interactions between Fish Species

A variety of environmental estrogens are commonly detected in human-impacted waterways. Although much is known about the effects of these environmental estrogens on the reproductive physiology and behavior of individuals within species, comparatively less is known about how these compounds alter the outcomes of interactions between species. Furthermore, few studies have considered how the effects of contaminants are modulated by natural variation in abiotic factors, such as temperature. To help fill this knowledge gap, we conducted a factorial experiment to examine the independent and combined effects of estrone (E1) and temperature on the outcome of predator-prey interactions between two common North American freshwater fishes, fathead minnows (Pimephales promelas) and bluegill sunfish (Lepomis macrochirus). Larval fathead minnows and adult sunfish were exposed to either a low (mean±standard deviation, 90.1 ± 18 ng/L; n = 16) or high (414 ± 147 ng/L; n = 15) concentration of E1 or to a solvent control for 30 days at one of four natural seasonal temperatures (15°C, 18°C, 21°C, and 24°C) before predation trials were performed. Exposure to E1 was associated with a significant increase in larval predation mortality that was independent of temperature. Across all temperature treatments, approximately 74% of control minnows survived; this survivorship significantly exceeded that of minnows exposed to either concentration of E1 (49% and 53% for minnows exposed to the low and high concentrations, respectively). However, exposure to E1 also impaired the prey-capture success of sunfish, partially mitigating predation pressure on exposed minnows. Overall prey-capture success by sunfish showed an inverted U-shaped distribution with temperature, with maximal prey consumption occurring at 21°C. This study illustrates the vulnerability of organismal interactions to estrogenic pollutants and highlights the need to include food web interactions in assessments of risk.

Mummichog (Fundulus heteroclitus) are less sensitive to 17α-ethinylestradiol (EE2) than other common model teleosts: A comparative review of reproductive effects

The environmental estrogen 17α-ethinylestradiol (EE₂) will depress or completely inhibit egg production in many common model teleosts at low concentrations (≤0.5 ng/L; Runnalls et al., 2015). This inhibition is not seen in the estuarine killifish, or mummichog (Fundulus heteroclitus), even when exposed to 100 ng/L EE₂. This relative insensitivity to EE₂ exposure indicates species-specific mechanisms for compensating for exogenous estrogenic exposure. This review compares various reproductive responses elicited by EE₂ in mummichog to other common model teleosts, such as zebrafish (Danio rerio) and fathead minnow (Pimephales promelas), identifying key endpoints where mummichog differ from other studied fish. For example, EE₂ accumulates primarily in the liver/gall bladder of mummichog, which is different than zebrafish and fathead minnow in which accumulation is predominantly in the carcass. Despite causing species-specific differences in fecundity, EE₂ has been shown to consistently induce hepatic vitellogenin in males and cause feminization/sex reversal during gonadal differentiation in larval mummichog, similar to other species. In addition, while gonadal steroidogenesis and plasma steroid levels respond to exogenous EE_2, it is generally at higher concentrations than observed in other species. In mummichog, production of 17β-estradiol (E₂) by full grown ovarian follicles remains high; unlike other teleost models where E₂ synthesis decreases as 17α,20β-dihydroxy-4-prenen-3-on levels increase to induce oocyte maturation. New evidence in mummichog indicates some dissimilarity in gonadal steroidogenic gene expression responses compared to gene expression responses in zebrafish and fathead minnow exposed to EE₂. The role of ovarian physiology continues to warrant investigation regarding the tolerance of mummichog to exogenous EE₂ exposure. Here we present a comprehensive review, highlighting key biological differences in response to EE₂ exposure between mummichog and other commonly used model teleosts.