Impaired Reproduction in Three-Spined Sticklebacks Exposed to Ethinyl Estradiol as Juveniles1

Anthropogenic stressors and the marine environment: From sources and impacts to solutions and mitigation

Human-released contaminants are often poorly understood wholistically in marine ecosystems. This review examines the sources, pathways, impacts on marine animals, and mitigation strategies of five pollutants (plastics, per- and polyfluoroalkyl substances, bisphenol compounds, ethynylestradiol, and petroleum hydrocarbons). Both abiotic and biotic mechanisms contribute to all five contaminants' movement. These pollutants cause short- and long-term effects on many biological processes genetically, molecularly, neurologically, physiologically, reproductively, and developmentally. We explore the extension of adverse outcome pathways to ecosystem effects by considering known inter-generational and trophic relations resulting in large-scale direct and indirect impacts. In doing so, we develop an understanding of their roles as environmental stressors in marine environments for targeted mitigation and future work. Ecosystems are interconnected and so international collaboration, standards, measures preceding mass production, and citizen involvement are required to protect and conserve marine life.

Early-life phenanthrene exposure inhibits reproductive ability in adult zebrafish and the mechanism of action

Phenanthrene (Phe) is a representative polycyclic aromatic hydrocarbon, and its ubiquity makes the risk assessment of Phe in aquatic ecosystems important. To assess the long-term effects of early-life Phe exposure on fish, the embryos of the model organism, zrbrafish (Danio rerio) were exposed to Phe at 0.05, 0.5, 5 and 50 nmol/L for 96 h and then raised to adulthood in clean water. Gonad development and reproductive functions were investigated in 120 day-old fish. The results showed that the percentage of spermatozoa in males and mature oocytes in females were decreased. The spawned egg numbers and the fertilization rate were reduced when the treated fish were mated with untreated fish. The transcription of genes involved in the brain-pituitary-gonadal axis was downregulated. The levels of both 17β-estradiol and testosterone were significantly decreased in the 5 and 50 nmol/L groups compared with the control group. The methylation levels in the promotor of gnrh3 (encoding gonadotropin releasing hormone) were significantly elevated in the adult fish in the 5 and 50 nmol/L treatments, which might be associated with the downregulation of gnrh3 transcription. These results suggested that embryonic exposure to Phe can inhibit the reproductive ability of adult fish, which should be adequately emphasized in its risk assessment.

Exposure to 17β estradiol causes erosion of sexual dimorphism in Bluegill (Lepomis macrochirus)

Estrogenic compounds including 17β estradiol (or E2) are known to negatively affect the reproductive system of many animals, including fish, leading to feminization, altered sex ratio, reduced fecundity, and decreased gonadosomatic index. The objective of this study was to evaluate the effects of varying concentrations of water-soluble 17β estradiol exposure on the external morphology of Bluegill. An experiment was set up where fish were individually maintained in 10-g tanks and exposed to 17β estradiol concentrations of 40 and 80 ng/L or no 17β estradiol exposure (the control). Fish were exposed for 21 days, with 17β estradiol replenished each week to account for 17β estradiol half-life. Fish were photographed laterally before and after the 21-day exposure to 17β estradiol. Landmark-based geometric morphometrics were conducted in MorphoJ and canonical variate and discriminant function analysis were used to compare the morphological changes in the fish under 17β estradiol exposure. The results showed that 17β estradiol exposure caused male dimorphic characters to change in Bluegill by becoming less prevalent. Specifically, there was a narrowing of the caudal peduncle, smaller nape protrusion, reduced opercular flap and pectoral fin, and a deeper body in the exposed groups compared with control fish under both concentrations. This research highlights the widespread effects of 17β estradiol on fish health beyond the reproductive system, which could have important conservation implications by affecting mate selection and reducing reproductive success.

Altered non-reproductive behavior and feminization caused by developmental exposure to 17α-ethinylestradiol persist to adulthood in three-spined stickleback (Gasterosteus aculeatus)

The synthetic estrogen 17α-ethinylestradiol (EE₂), ubiquitous in the aquatic environment and commonly detected in sewage effluents, interferes with the endocrine system in multiple ways. Exposure during sensitive windows of development causes persistent effects on fertility, reproductive and non-reproductive behavior in mammals and fish. In the present study, three-spined stickleback (Gasterosteus aculeatus) were exposed to nominal 0 and 20 ng/L EE₂ from fertilization to 7 weeks post-hatch. After 8 months of remediation in clean water three non-reproductive behaviors, not previously analyzed in developmentally EE₂-exposed progeny of wild-caught fish, were evaluated. Chemical analysis revealed that the nominal 0 and 20 ng/L exposure contained 5 and 30 ng/L EE_2, respectively. Therefore, the use of control fish from previous experiments was necessary for comparisons. Fish exposed during development showed significant concentration-dependent reduction in anxiety-like behavior in the scototaxis (light/dark preference) test by means of shorter latency to first entrance to the white compartment, more visits in white, and longer total time in white compared to unexposed fish. In the novel tank test, developmental exposure significantly increased the number of transitions to the upper half of the aquaria. Exposure to EE₂ during development did not alter shoal cohesion in the shoaling test compared with unexposed fish but fish exposed to 30 ng/L EE₂ had significantly longer latency to leave the shoal and fewer transitions away from the shoal compared to fish exposed to 5 ng/L EE₂. Skewed sex ratio with more females, sex reversal in genetic males as well as intersex in males was observed after exposure to 30, but not 5 ng/L EE₂. In conclusion, EE₂ exposure during development in three-spined stickleback resulted in persistent effects on anxiety-like behaviors. These long-term effects from developmental exposure are likely to be of higher relevance for natural populations than are short-term effects from adult exposure.

Embryonic exposure to benzo(a)pyrene inhibits reproductive capability in adult female zebrafish and correlation with DNA methylation

This study was conducted to investigate the effects of embryonic short-term exposure to benzo(a)pyrene (BaP), a model polycyclic aromatic hydrocarbon, on ovarian development and reproductive capability in adult female zebrafish. In 1-year-old fish after embryonic exposure to BaP for 96 h, the gonadosomatic indices and the percentage of mature oocytes were significantly decreased in the 0.5, 5 and 50 nmol/L treatments. The spawned egg number, the fertilization rate and the hatching success were significantly reduced, while the malformation rate of the F1 unexposed larvae were increased. The mRNA levels of follicle-stimulating hormone, luteinizing hormone, ovarian cytochrome P450 aromatase cyp19a1a and cyp19b, estrogen receptor esr1 and esr2, and hepatic vitellogenin vtg1 and vtg2 genes, were down-regulated in adult female zebrafish that were exposed to BaP during embryonic stage. Both 17β-estradiol and testosterone levels were reduced in the ovary of adult females. The methylation levels of the gonadotropin releasing hormone (GnRH) gene gnrh3 were significantly increased in the adult zebrafish brain, and those of the GnRH receptor gene gnrhr3 were elevated both in the larvae exposed to BaP and in the adult brain, which might cause the down-regulation of the mRNA levels of gnrh3 and gnrhr3. This epigenetic change caused by embryonic exposure to BaP might be a reason for physiological changes along the brain-pituitary-gonad axis. These results suggest that short-term exposure in early life should be included and evaluated in any risk assessment of pollutant exposure to the reproductive health of fish.

Molecular characterisation of oestrogen receptor ERα and the effects of bisphenol A on its expression during sexual development in the Chinese giant salamander (Andrias davidianus)

The aim of this study was to characterise the molecular structure of the oestrogen receptor ERα and to evaluate the effect of bisphenol A (BPA) on ERα expression during sexual development of the Chinese giant salamander (Andrias davidianus). The ERα cDNA of A. davidianus includes an open reading frame of 1755bp (encoding 584 amino acids), a 219-bp 5' untranslated region (UTR) and a 611-bp 3'UTR. A polyadenylation signal was not found in the 3'UTR. Amino acid sequence analysis showed high homology between ERα of A. davidianus and that of other amphibians, such as Andrias japonicas (99.66% identity) and Rana rugose (81.06% identity). In 3-year-old A. davidianus, highest ERα expression was observed in the liver and gonads. During different developmental stages in A. davidianus (from 1 to 3 years of age), ERα expression in the testes increased gradually. ERα was localised in the epithelial cells of seminiferous lobules and in interstitial cells. ERα-positive cells were more abundant in the interstitial tissue during testicular development. ERα was located in the nucleus of oocytes during ovary development. We found that the sex of 6-month-old A. davidianus larvae could not be distinguished anatomically. The sex ratio did not change after larvae were treated with 10μM BPA for 1 month. However, BPA treatment reduced bodyweight and ERα expression in the gonads in male larvae.

Testis transcriptome alterations in zebrafish (Danio rerio) with reduced fertility due to developmental exposure to 17α-ethinyl estradiol

17α-Ethinylestradiol (EE₂) is a ubiquitous aquatic contaminant shown to decrease fish fertility at low concentrations, especially in fish exposed during development. The mechanisms of the decreased fertility are not fully understood. In this study, we perform transcriptome analysis by RNA sequencing of testes from zebrafish with previously reported lowered fertility due to exposure to low concentrations of EE₂ during development. Fish were exposed to 1.2 and 1.6 ng/L (measured concentration; nominal concentrations 3 and 10 ng/L) of EE₂ from fertilization to 80 days of age, followed by 82 days of remediation in clean water. RNA sequencing analysis revealed 249 and 16 genes to be differentially expressed after exposure to 1.2 and 1.6 ng/L, respectively; a larger inter-sample variation was noted in the latter. Expression of 11 genes were altered by both exposures and in the same direction. The coding sequences most affected could be categorized to the putative functions cell signalling, proteolysis, protein metabolic transport and lipid metabolic process. Several homeobox transcription factors involved in development and differentiation showed increased expression in response to EE₂ and differential expression of genes related to cell death, differentiation and proliferation was observed. In addition, several genes related to steroid synthesis, testis development and function were differentially expressed. A number of genes associated with spermatogenesis in zebrafish and/or mouse were also found to be differentially expressed. Further, differences in non-coding sequences were observed, among them several differentially expressed miRNA that might contribute to testis gene regulation at post-transcriptional level. This study has generated insights of changes in gene expression that accompany fertility alterations in zebrafish males that persist after developmental exposure to environmental relevant concentrations of EE₂ that persist followed by clean water to adulthood. Hopefully, this will generate hypotheses to test in search for mechanistic explanations.

Biodegradation of 17β-estradiol by Bacterial Co-culture Isolated from Manure

Animal wastes are potential sources of natural and steroidal estrogen hormones into the environment. These hormones can be removed by microorganisms with induced enzymes. Two strains of 17β-estradiol-degrading bacteria (LM1 and LY1) were isolated from animal wastes. Based on biochemical characteristics and 16 S rDNA gene sequences, we identified strains LM1 and LY1 as belonging to the genus of Acinetobacter and Pseudomonas, respectively. Bacterial co-culture containing LM1 and LY1 bacterial strains could rapidly remove approximately 98% of E2 (5 mg L⁻¹) within 7 days. However, strains LM1 and LY1 degraded 77% and 68% of E2 when they were incubated alone, respectively. More than 90% of 17β-estradiol (E2, ≤ 20 mg L⁻¹) could be removed by bacterial co-culture. Low C/N ratio (1:35) was more suitable for bacterial growth and E2 degradation. The optimal pH for bacterial co-culture to degrade E2 ranged from 7.00 to 9.00. Coexisting sodium acetate, glucose and sodium citrate decreased E2 degradation in the first 4 days, but more E2 was removed when they were depleted. The growth of the bacterial co-culture was not significantly decreased by Ni, Pb, Cd or Cu at or below 0.8, 1.2, 1.6 or 0.8 mg L⁻¹, respectively. These data highlight the usefulness of bacterial co-culture in the bioremediation of estrogen-contaminated environments.

The agricultural contaminant 17β-trenbolone disrupts male-male competition in the guppy (Poecilia reticulata)

Despite a growing literature highlighting the potential impact of human-induced environmental change on mechanisms of sexual selection, relatively little is known about the effects of chemical pollutants on male-male competition. One class of environmental pollutant likely to impact male competitive interactions is the endocrine-disrupting chemicals (EDCs), a large and heterogeneous group of chemical contaminants with the potential to influence morphology, physiology and behaviour at minute concentrations. One EDC of increasing concern is the synthetic, androgenic steroid 17β-trenbolone, which is used globally to promote growth in beef cattle. Although 17β-trenbolone has been found to cause severe morphological and behavioural abnormalities in fish, its potential impact on male-male competition has yet to be investigated. To address this, we exposed wild male guppies (Poecilia reticulata) to an environmentally realistic concentration of 17β-trenbolone (average measured concentration: 8 ng/L) for 21 days using a flow-through system. We found that, in the presence of a competitor, 17β-trenbolone-exposed males carried out more frequent aggressive behaviours towards rival males than did unexposed males, as well as performing less courting behaviour and more sneak (i.e., coercive) mating attempts towards females. Considering that, by influencing mating outcomes, male-male competition has important consequences for population dynamics and broader evolutionary processes, this study highlights the need for greater understanding of the potential impact of EDCs on the mechanisms of sexual selection.

Delayed impacts of developmental exposure to 17-α-ethinylestradiol in the self-fertilizing fish Kryptolebias marmoratus

17-α-ethinylestradiol (EE2) is one of the most potent endocrine disrupting compounds found in the aquatic environments, and is known to strongly alter fish reproduction and fitness. While the effects of direct exposure to EE2 are well studied in adults, there is an increasing need to assess the impacts of exposure during early life stages. Sensitivity to pollutants during this critical window can potentially affect the phenotype later in life or in subsequent generations. This study investigated phenotypic outcome of early-life exposure to 17-α-ethinylestradiol during development and in adults of the mangrove rivulus, Kryptolebias marmoratus. Being one of the only two known self-fertilizing hermaphroditic vertebrates, this fish makes it possible to work with genetically identical individuals. Therefore, using rivulus makes it possible to examine, explicitly, the phenotypic effects of environmental variance while eliminating the effects of genetic variance. Genetically identical rivulus were exposed for the first 28days post hatching (dph) to 0, 4 or 120ng/L of EE2, and then were reared in uncontaminated water until 168dph. Growth, egg laying and steroid hormone levels (estradiol, cortisol, 11-ketotestosterone, testosterone) were measured throughout development. Exposed fish showed a reduction in standard length directly after exposure (28dph), which was more pronounced in the 120ng/L group. This was followed by compensatory growth when reared in clean water: all fish recovered a similar size as controls by 91dph. There was no difference in the age at maturity and the proportions of mature, non-mature and male individuals at 168dph. At 4ng/L, fish layed significantly fewer eggs than controls, while, surprisingly, reproduction was not affected at 120ng/L. Despite a decrease in fecundity at 4ng/L, there were no changes in hormones levels at the lower concentration. In addition, there were no significant differences among treatments immediately after exposure. However, 120ng/L exposed fish exhibited significantly higher levels of testosterone at 91 and 168dph and 11-ketotestosterone at 168dph, up to 140days after exposure. These results indicate that early-life exposure to EE2 had both immediate and delayed impacts on the adult's phenotype. While fish growth was impaired during exposure, compensatory growth, reduced fecundity and modification of the endocrine status were observed after exposure ceased.

Changes in reproductive physiology of mangrove rivulus Kryptolebias marmoratus following exposure to environmentally relevant doses of ethinyl oestradiol

Kryptolebias marmoratus exposed to 4 ng l(-1) of ethinyl oestradiol (EE2) for 30 days experienced significant changes in endogenous 17β-oestradiol (E2) and 11-ketotestosterone (KT) and qualitative changes in gonad morphology. Both hermaphrodites and males showed a significant decrease in E2, whereas only males exhibited a significant decrease in KT. Exposure to EE2 resulted in a decrease in spermatid and spermatocyte density in males and an increase in the number of early stage oocytes in hermaphrodites.

Biomarker responses to estrogen and androgen exposure in the brook stickleback (Culaea inconstans): A new bioindicator species for endocrine disrupting compounds

Small-bodied freshwater fish are commonly used in regulatory testing for endocrine disrupting compounds (EDCs) but most lack a sensitive and quantifiable androgen-specific biomarker. Brook stickleback (Culaea inconstans) are a North American freshwater fish whose males produce an androgen-regulated glycoprotein in the kidney called spiggin. Although spiggin induction in females has been used as an androgen-specific biomarker of exposure in other stickleback species it has not been characterized in brook stickleback. Therefore, our objective was to develop a bioassay using brook stickleback to measure estrogenic and androgenic responses and establish the sensitivity of traditional and novel biomarkers of exposure. We first developed and optimized a qPCR assay to measure spiggin and vitellogenin transcript levels in kidney and liver tissue, respectively. Basal levels were differentially expressed in mature wild-caught male and female brook stickleback. To determine their sensitivity to EDCs, fish were exposed to nominal concentrations of 1, 10 and 100ng/L of 17α-methyltestosterone (MT) or 17α-ethinylestradiol (EE2) for 21days (sampled at 7 and 21days) under semi-static renewal conditions. MT and EE2 exposure induced spiggin and vitellogenin transcripts in female kidneys and male livers, respectively. Exposure to EE2 also increased hepatosomatic index in both sexes and decreased gonadosomatic index in females. Histopathological alterations were observed in the kidney of EE2-exposed fish and an increase in kidney epithelium cell height occurred in MT-exposed females. Given the sensitivity of these endpoints, the brook stickleback is a promising new freshwater fish model for EDC evaluation and a potential bioindicator for EDCs in North American freshwater environments.

Exposure to an agricultural contaminant, 17β-trenbolone, impairs female mate choice in a freshwater fish

Despite the pivotal role sexual selection plays in population dynamics and broader evolutionary processes, the impact of chemical pollution on female mate choice is poorly understood. One group of chemical contaminants with the potential to disrupt the mechanisms of female mate choice is endocrine disrupting chemicals (EDCs); a broad class of environmental pollutants that can interfere with the endocrinology of organisms at extremely low concentrations. Recent research has revealed that estrogenic EDCs can affect female mate choice in fish, but the impact of androgenic EDC exposure is yet to be studied. To address this, we investigated the effects of an environmentally relevant concentration of trenbolone - an androgenic steroid used as a growth promoter in the cattle industry - on female mate choice in wild-caught guppies (Poecilia reticulata). We exposed male and female guppies to 17β-trenbolone for 21 days (measured concentration 4ng/L) via a flow-through system, and found that trenbolone-exposed female guppies spent less time associating with males, and were less choosy, compared to unexposed females. In contrast, trenbolone had no impact on male reproductive behavior or morphology. This is the first study to show that androgenic EDC exposure can disrupt female mate choice, highlighting the need for studies to investigate the behavioral impacts of environmental contaminants on both sexes.

Risk of endocrine disruption to fish in the Yellow River catchment in China assessed using a spatially explicit model

The global water availability assessment (GWAVA) model, incorporating regional water abstractions and reservoir information, was used to model the human-sourced steroid estrogens estrone (E1) and estradiol (E2) in the Yellow River catchment (China). The river flows in the main stem were calibrated using gauged flows. Following a review of Chinese data on estrogen discharge from a range of sewage treatment plants, low, median, and high discharge rates were identified and used as best, expected, and worst-case scenarios, respectively. For any given location, the temporal variation of modeled estrogen levels was summarized using the mean and upper 90th percentile, which is where the model predicts 90% of values would be below this concentration. The predicted means and 90th percentiles for E1 were comparable to previous E1 measurements reported in the river. For the whole catchment, only 19% (mean value) of the river system by length was predicted to exceed 1 ng/L E2 equivalents (EEQs) using expected estrogen sewage discharge. Only 3% of the network by length was predicted to exceed the dangerously high 10 ng/L EEQ when considering 90th percentile concentrations. The highest exposures were in the Fen and Wei tributaries. Endocrine disruption risk from estrogens was predicted to be minimal in the main stem. Only in the worst-case discharge scenario and 90th percentile predicted concentrations were the most downstream river reaches of the main stem predicted to be at risk. Reservoirs appeared to be helpful in reducing estrogen concentrations thanks to longer water residence facilitating biodegradation.

Pharmaceuticals and personal care products: A critical review of the impacts on fish reproduction

Research in environmental toxicology involving pharmaceuticals and personal care products (PPCPs) has increased greatly over the last 10-15 years. Much research has been focused on the endocrine-disrupting potential of PPCPs, as they relate to negative population impacts of aquatic organisms. This review assesses the current data on the reported effects of PPCPs on fish reproduction with an emphasis on fecundity, a predictor of population effects. Studies of both individual PPCPs and PPCP mixtures are presented. As the majority of individual PPCP studies reviewed demonstrate negative effects on fish fecundity, we relate these findings to detected surface water concentrations of these compounds. Very few studies involving PPCP mixtures have been conducted; however, the need for these types of studies is warranted as fish are most likely exposed to mixtures of PPCPs in the wild. In addition, laboratory and field assessments of wastewater treatment plant (WWTP) effluents, a major source of PPCPs, are reviewed. Much of the data provided from these assessments are variable and do not generally demonstrate negative impacts on reproduction, or the studies are unable to directly associate observed effects with WWTP effluents. Finally, future research considerations are outlined to provide an avenue into understanding how wild populations of fish are affected by PPCPs. These considerations are aimed at determining the adaptation potential of fish exposed to mixtures of PPCPs over multiple generations. As global use of PPCPs continually rises, the need to discern the effects of chronic exposure to PPCPs is greatly increased.

Mixture effects of levonorgestrel and ethinylestradiol: estrogenic biomarkers and hormone receptor mRNA expression during sexual programming

Synthetic progesterone (progestins) and estrogens are widely used pharmaceuticals. Given that their simultaneous unintentional exposure occurs in wildlife and also in human infants, data on mixture effects of combined exposures to these hormones during development is needed. Using the Xenopus (Silurana) tropicalis test system we investigated mixture effects of levonorgestrel (LNG) and ethinylestradiol (EE2) on hormone sensitive endpoints. After larval exposure to LNG (0.1nM), or EE2 (0.1nM) singly, or in combination with LNG (0.01, 0.1, 1.0nM), the gonadal sex ratio was determined histologically and hepatic mRNA levels of genes encoding vitellogenin (vtg beta1) and the estrogen (esr1, esr2), progesterone (ipgr) and androgen (ar) receptors were quantified using quantitative PCR. All EE2-exposed groups showed female-biased sex ratios and increased vtg beta1 mRNA levels compared with the controls. Compared with the EE2-alone group (positive control) there were no significant alterations in vtg beta1 levels or in sex ratios in the co-exposure groups. Exposure to LNG-alone caused an increase in ar mRNA levels in females, but not in males, compared to the controls and the co-exposed groups, indicating that co-exposure to EE2 counteracted the LNG-induced ar levels. No treatment related impacts on the mRNA expression of esr1, esr2, and ipgr in female tadpoles were found, suggesting that these endpoints are insensitive to long-term exposure to estrogen or progestin. Due to the EE2-induced female-biased sex ratios, the mRNA expression data for the low number of males in the EE2-exposed groups were not statistically analyzed. In conclusion, our results suggest that induced vtg expression is a robust biomarker for estrogenic activity in exposure scenarios involving both estrogens and progestins. Developmental exposure to LNG caused an induction of hepatic ar mRNA expression that was antagonized by combined exposure to EE2 and LNG. To our knowledge this is the first study to report effects of combined exposures to EE2 and LNG during the period of sexual programming.

Recovery of a wild fish population from whole-lake additions of a synthetic estrogen

Despite widespread recognition that municipal wastewaters contain natural and synthetic estrogens, which interfere with development and reproduction of fishes in freshwaters worldwide, there are limited data on the extent to which natural populations of fish can recover from exposure to these compounds. We conducted whole-lake additions of an active component of the birth control pill (17α-ethynylestradiol; EE2) that resulted in the collapse of the fathead minnow (Pimephales promelas) population. Here we quantify physiological, population, and genetic characteristics of this population over the 7 years after EE2 additions stopped to determine if complete recovery was possible. By 3 years post-treatment, whole-body vitellogenin concentrations in male fathead minnow had returned to baseline, and testicular abnormalities were absent. In the spring of the fourth year, adult size-frequency distribution and abundance had returned to pretreatment levels. Microsatellite analyses clearly showed that postrecovery fish were descendants of the original EE2-treated population. Results from this whole-lake experiment demonstrate that fish can recover from EE2 exposure at the biochemical through population levels, although the timelines to do so are long for multigenerational exposures. These results suggest that wastewater treatment facilities that reduce discharges of estrogens and their mimics can improve the health of resident fish populations in their receiving environments.

Exposure to 17α-ethinylestradiol decreases motility and ATP in sperm of male fighting fish Betta splendens

The synthetic estrogen 17α-ethinylestradiol (EE2) is an endocrine-disrupting chemical released into aquatic environments from sewage treatment facilities. We tested the effects of two environmentally relevant concentrations of waterborne EE2, 10 and 100 ng L(-1) , on reproductive endpoints in the teleost fish Betta splendens. In the first experiment, testes were removed from males and sperm were exposed to EE2 directly through the activation water. Direct exposure to EE2 had no effect on any measure of sperm swimming performance. In the second experiment, we exposed sexually mature male B. splendens to EE2 using a semi-static exposure protocol for 4 weeks. There were no significant treatment effects in the 10 ng L(-1) treatment group, but at the 100 ng L(-1) dose we found that fish had smaller gonads and reduced sperm swimming velocity. When allowed to interact freely with female conspecifics, males exposed to 100 ng L(-1) EE2 built smaller nests and showed a nonsignificant decrease in fertilization success. To investigate further the potential mechanism underlying the decrease in sperm quality, we repeated the chronic exposure experiment and analyzed the ATP content of sperm from fish in each treatment group. We found that males exposed to 100 ng L(-1) of EE2 had fewer moles of ATP per sperm than did fish in the other two treatment groups, suggesting that a decrease in intracellular ATP caused a reduction in sperm swimming velocity. The current study adds to the growing body of literature that indicates the risks to aquatic organisms of exposure to environmentally relevant concentrations of EE2.

Intersex in teleost fish: are we distinguishing endocrine disruption from natural phenomena?

Intersex is defined as the simultaneous presence of male and female gonadal tissue in a gonochoristic (fixed-sex) species. The intersex condition has been documented in both wild and laboratory animals, including fish, amphibians, and reptiles. In aquatic animals, intersex is often viewed as a signature effect of exposure to endocrine disrupting compounds. At least 37 fish species from 17 families have been identified with intersex gonads in 54 field survey studies. However, reports of the occurrence of intersex at reference sites have led to speculation that a baseline level of intersex is "normal". The objective of this critical review was to assess factors potentially associated with baseline levels of intersex in fish and to examine the mechanisms involved in the intersex condition in order to identify priority research areas. Based on current literature, the relationship between intersex and physiological parameters such as plasma sex steroids and vitellogenin is not well characterized or conclusive. Moreover, the literature is not definitive on whether field studies are distinguishing between natural intersex and intersex due to stressors. High throughput transcriptomics will improve understanding of how intersex condition manifests after exposure to aquatic pollution and it is recommended that studies consider both males with and without intersex that inhabit the same polluted site in order to differentiate pathways associated with xenobiotic responses versus molecular pathways associated with intersex. Other experimental design considerations for field studies examining intersex include data collection on life history (e.g. migratory patterns) and improved reference site characterization.

Parental exposure to methyl methane sulfonate of three-spined stickleback: contribution of DNA damage in male and female germ cells to further development impairment in progeny

Data regarding the link between DNA integrity of germ cells and the quality of progeny in fish exposed to genotoxicant are scarce although such information is of value to understand genotoxic effects of contaminants in aquatic fauna. This work aimed at studying the consequences of a parental exposure during the breeding season on offspring quality in three-spined stickleback. After in vivo exposure of adult fish to methyl methane sulfonate, a model alkylating compound, a clear increase in DNA damage was observed in erythrocytes of both genders, here used as a biomarker of exposure. MMS exposure significantly affected sperm DNA integrity but neither female fecundity nor fertilization success. In order to understand the contribution of each sex to potential deleterious effects in progeny due to parental exposure, mating of males and females exposed or not to MMS, was carried out. Exposure of both males and females or of males alone led to a significant increase in both mortality during embryo-larval stages and abnormality rate at hatching that appeared to be sensitive stages. Thus, in accordance with recent studies carried out in other freshwater fish species, such development defects in progeny were clearly driven by male genome, known to be devoid of DNA repair capacity in spermatozoa. The next step will be to investigate the link between DNA damage in stickleback sperm and reproductive impairment in natural populations exposed to complex mixture of genotoxicants.

Reproductive impairment and endocrine disruption in goldfish by feeding diets containing soybean meal

A long-term feeding experiment was conducted to investigate the inclusion of soybean meal in diets for goldfish (Carassius auratus) on fish reproduction. In the present study, 20 weeks after hatching, goldfish with an initial average weight of 2±0.03g (mean±SD) were divided into 12 groups (three tanks per dietary treatment) and fed 400gkg(-1) crude protein diets. The four experimental diets were as follows: diet 1, fish meal (FM); diet 2, 35% soybean meal (SBM35%); diet 3, 65% soybean meal (SBM65%); diet 4, 100% soybean meal (SBM100%). After feeding with experimental diets, the impact on reproduction was investigated. In both males and females, the plasma testosterone (T) was significantly decreased, while 17β-estradiol (E2) levels were significantly increased. Levels of 17α, hydroxyprogesterone. (17-OH-P) did not differ as a result of soybean meal feeding in either males or females. The average number of eggs spawned and sperm quality were reduced on feeding with soybean inclusion. Histological examination showed impact on oocyte maturation progress and spermatogenesis process in female and male fish, respectively. In addition, feeding goldfish with soybean meal until maturation caused reduction in fertilization and hatching rates in parallel to increasing soybean meal inclusion. The results demonstrated that inclusion of soybean meal might cause sex hormone biosynthesis disruption and reproductive impairments in fish, ultimately decreased fertilization as well as hatching rates in the offspring.

An androgenic agricultural contaminant impairs female reproductive behaviour in a freshwater fish

Endocrine disrupting chemicals (EDCs) are a large group of environmental pollutants that can interfere with the endocrine system function of organisms at very low levels. One compound of great concern is trenbolone, which is widely used as a growth promoter in the cattle industry in many parts of the world. The aim of this study was to test how short-term (21-day) exposure to an environmentally relevant concentration of 17β-trenbolone (measured concentration 6 ng/L) affects reproductive behaviour and fin morphology in the eastern mosquitofish (Gambusia holbrooki). The mosquitofish is a sexually dimorphic livebearer with males inseminating females using their modified anal fin, the gonopodium, as an intromittent organ. Although the species has a coercive mating system, females are able to exert some control over the success of male mating attempts by selectively associating with, or avoiding, certain males over others. We found that females exposed to trenbolone approached males less and spent more time swimming away from males than non-exposed (control) females. By contrast, we found no difference in the behaviour of exposed and non-exposed males. Furthermore, exposure did not affect the anal fin morphology of males or females. This is the first study to demonstrate that exposure to an androgenic EDC can impair female (but not male) behaviour. Our study illustrates how anthropogenic contaminants can have sex-specific effects, and highlights the need to examine the behavioural responses of environmental contaminants in both sexes.

Effects of chronic exposures to the herbicides atrazine and glyphosate to larvae of the threespine stickleback (Gasterosteus aculeatus)

Atrazine (ATR) and glyphosate (GLY) are among the most widely used herbicides in Canada, yet there is relatively little information concerning their toxicity to early life stages of marine fish. The threespine stickleback (Gasterosteus aculeatus) reproduces in coastal habitats which receive runoff of pesticides during the summer, the peak season of herbicide use. Sticklebacks have biomarkers for effects of both estrogenic and androgenic contaminants. Stickleback adults from a clean reference site were allowed to reproduce in the laboratory and the fertilized eggs were incubated until hatching. Larval sticklebacks (<24h old) were exposed for 42 d to four concentrations (0.1, 1, 10 and 100 μg/l) of either ATR or GLY, a seawater control, a carrier (acetone) control and positive controls for estrogenic (0.05 μg/l ethinylestradiol, EE2) and androgenic (3 μg/l dihydrotestosterone, DHT) effects. The survivors were measured (length, wet weight) then conserved for biochemical (vitellogenin, VTG, and the male nest-protein spiggin, SPG) and histological (phenotypic sex determination) analyses. There were no significant effects of ATR and GLY exposures on larval survival or growth. Exposure to 3 μg DHT/l resulted in a significant effect on growth (body lengths) but did not induce SPG, possibly because of DHT degradation after the 24h solution renewal. VTG was induced after the EE2 exposure, yet neither ATR nor GLY induced production of VTG and SPG. The proportion of mixed sex individuals was higher in the positive controls compared to the negative controls. A single mixed sex individual was found in the group exposed to the lowest dose of atrazine and none in glyphosate expositions. We conclude that these herbicides do not show estrogenic or androgenic effects to early life stages of sticklebacks at environmentally realistic concentrations.

The effects of short-term exposure to an endocrine disrupter on behavioral consistency in male juvenile and adult Siamese fighting fish

17α-Ethinyloestradiol (EE2) is known to impact courtship and aggression but how exposure affects the consistency with which individuals express these behaviors over time is not commonly addressed. In addition, how juvenile and adult male fish differ in levels of behavioral consistency, both before and after EE2 exposure, is unknown. To examine these questions, juvenile and adult male Siamese fighting fish were presented with a dummy male and dummy female simultaneously both before and after acute exposure to a nominal (15 ng/L) dose of EE2. Multiple trials were conducted to measure how consistent individual differences are affected by age and EE2 exposure. Both female- and male-directed behaviors decreased after short-term exposure to EE2. Juvenile and adult fish differed in the number of female-directed tail beats and bites they performed, with adult fish performing more tail beats and juvenile fish performing more bites. EE2 exposure had a greater effect on consistent individual differences in female-directed than in male-directed behaviors, which may be a byproduct of intense artificial selection for aggression in this species. Repeatability values were lower both before and after exposure in juvenile than in adult fish, suggesting that individuals become more consistent with age. This study suggests that male Siamese fighting fish vary in their sensitivity to short-term EE2 exposure and stresses the importance of examining behavior over multiple time points both within and across age classes to gain a more thorough understanding of the effects of endocrine disruptors on behavior.

Brain circuit imprints of developmental 17α-Ethinylestradiol exposure in guppies (Poecilia reticulata): persistent effects on anxiety but not on reproductive behaviour

The effects of endocrine disruptors may vary with the timing of exposure. The physiological implications of adult exposure are present during and shortly after exposure while embryonic exposure can imprint changes manifested in adulthood. In this study, guppy (Poecilia reticulata) embryos were exposed to 2 and 20 ng/L of 17α-ethinylestradiol during development via the mother and reared in clean water from gestation until 6 months of age. As adults, fish exposed to 20 ng/L during development showed significantly altered behaviour in the Novel Tank test, where anxiety is determined as the tendency to remain at the bottom upon introduction into an unfamiliar tank. 17α-ethinylestradiol treatment increased the latency time before swimming to the upper half of the tank and decreased the number of transitions to the upper half. In control females the basal stress behaviour responses were significantly higher than in males, as indicated by longer latency period and fewer and shorter visits to the upper half, supporting the importance of gonadal hormones for the behaviour. The anxiety increased, however, with treatment in both sexes, suggesting that the observed response is not entirely due to feminisation of the males. Shoaling behaviour, analysed as tendency to leave a shoal of littermates, was neither sex-differentiated nor changed by treatment. Also male reproductive behaviour, brain aromatase activity and testes histology, previously shown to respond to oestrogen exposure in adult guppy, were unaffected by the developmental treatment. This suggests that the stress system in the guppy is very sensitive to 17α-ethinylestradiol, which possibly causes an early organisational imprint on the brain circuit that regulates stress reactions.

Creating females? Developmental effects of 17α-ethynylestradiol on the mangrove rivulus' ovotestis

Interest in the occurrence and fate of trace organic contaminants in the aquatic environment and their potential effects on all organisms has increased over the past two decades. Researches on contaminants have included both natural and synthetic estrogenic contaminants, neuroactive pharmaceuticals, and other endocrine disrupting chemicals that are mediated by the androgen and progesterone receptors. Exposure to very low concentrations (ng/L or parts per trillion) of compounds such as 17α-ethynylestradiol (EE(2)), a synthetic estrogen, can affect gonadal development, viability and production of eggs, fertilization rate, and sexual differentiation in fishes. Researchers and aquaculturists have used exposures to relatively higher concentrations of androgens and estrogens, for example 17α-methyltestosterone and EE(2), respectively, to direct sexual differentiation in a number of fishes. Rivulus is an androdioecious teleost that in nature exists mostly as selfing, simultaneous hermaphrodites as well as a small number of males that outcross with hermaphrodites. No one has either collected females in the wild or created functional females in the laboratory. This study had two goals: (1) to develop a reliable protocol to produce female rivulus to enable downstream technologies such as embryo injections and (2) to investigate developmental effects of EE(2) on the sexual outcome, reproductive health, and relevant gene expression in rivulus. With these goals in mind, we exposed newly hatched rivulus to nominal concentrations of 0.1, 0.5, or 1.0 parts per million (ppm) EE(2) for 4 weeks, grew them to maturity in control water, and then compared egg production; production and viability of embryos; age of reproductive maturity; and gene expression in the brain, gonad, and liver. Expression levels of seven genes with known relevance to gonadal development and function (cyp19a1b, cyp19a1a, dmrt1, figα, ERα, ERβ, and vtg) were measured using quantitative polymerase chain reaction (PCR). There was a significant decrease in cyp19a1a gene expression in the brain, corresponding to increased exposure to EE(2). Gonadal gene expression for cyp19a1a, ERα, and dmrt1 also decreased in response to EE(2). Vtg expression in the liver was unaffected. Our hypothesis that exposure to EE(2) during gonadal differentiation would direct female development was not supported by the data. However, treated fish exhibited impaired reproductive health that included reduced expression of relevant genes and, importantly, decreased fertility, increased sterility, and delay of age of reproductive maturity. The results of this study suggest that the development and maintenance of a simultaneous hermphrodite ovotestis may be particularly sensitive to its hormonal milieu.

Development of a molecular biomarker for detecting intersex after exposure of male medaka fish to synthetic estrogen

Although intersex of fish species has been widely reported in aquatic environments, there is no appropriate biomarker of the effects to assess the occurrence of intersex. In the present study, mRNA expression profiles of 14 genes, which are either involved in ovary development and maintenance or have relatively high mRNA transcription levels in ovarian gene expression profiles in fish species, were comprehensively evaluated in male Japanese medaka (Oryzias latipes) exposed to 17α-ethynylestradiol (EE2) to investigate their utility as indicators of the severity index of intersex. Of these 14 genes, mRNA expression of a novel gene, termed ovary structure protein 1 (OSP1) in the present study, showed female-like expression pattern with the highest transcription levels, and displayed the most significantly positive correlation with the severity index of intersex (r(2) =0.8215, p<0.0001). The full-length mRNA sequence of OSP1 is 802 bp, with an open reading frame (ORF) of 642 bp that encodes a 214-amino acid peptide. Reverse transcription polymerase chain reaction and in situ hybridization revealed that OSP1 was expressed exclusively in the ovaries, specifically in the oogonia and primary oocytes in ovaries and in testis with intersex. These results suggest that the analysis of mRNA expression of OSP1 can be used to indicate intersex in male medaka.

Comparative responsiveness to natural and synthetic estrogens of fish species commonly used in the laboratory and field monitoring

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.

Divergence in sex steroid hormone signaling between sympatric species of Japanese threespine stickleback

Sex steroids mediate the expression of sexually dimorphic or sex-specific traits that are important both for mate choice within species and for behavioral isolation between species. We investigated divergence in sex steroid signaling between two sympatric species of threespine stickleback (Gasterosteus aculeatus): the Japan Sea form and the Pacific Ocean form. These sympatric forms diverge in both male display traits and female mate choice behaviors, which together contribute to asymmetric behavioral isolation in sympatry. Here, we found that plasma levels of testosterone and 17β-estradiol differed between spawning females of the two sympatric forms. Transcript levels of follicle-stimulating hormone-β (FSHβ) gene were also higher in the pituitary gland of spawning Japan Sea females than in the pituitary gland of spawning Pacific Ocean females. By contrast, none of the sex steroids examined were significantly different between nesting males of the two forms. However, combining the plasma sex steroid data with testis transcriptome data suggested that the efficiency of the conversion of testosterone into 11-ketotestosterone has likely diverged between forms. Within forms, plasma testosterone levels in males were significantly correlated with male body size, a trait important for female mate choice in the two sympatric species. These results demonstrate that substantial divergence in sex steroid signaling can occur between incipient sympatric species. We suggest that investigation of the genetic and ecological mechanisms underlying divergence in hormonal signaling between incipient sympatric species will provide a better understanding of the mechanisms of speciation in animals.

The interruption of thyroid and interrenal and the inter-hormonal interference in fish: does it promote physiologic adaptation or maladaptation?

Endocrines, the chief components of chemical centers which produce hormones in tune with intrinsic and extrinsic clues, create a chemical bridge between the organism and the environment. In fishes also hormones integrate and modulate many physiologic functions and its synthesis, release, biological actions and metabolic clearance are well regulated. Consequently, thyroid hormones (THs) and cortisol, the products of thyroid and interrenal axes, have been identified for their common integrative actions on metabolic and osmotic functions in fish. On the other hand, many anthropogenic chemical substances, popularly known as endocrine disrupting chemicals, have been shown to disrupt the hormone-receptor signaling pathways in a number fish species. These chemicals which are known for their ability to induce endocrine disruption particularly on thyroid and interrenals can cause malfunction or maladaptation of many vital processes which are involved in the development, growth and reproduction in fish. On the contrary, evidence is presented that the endocrine interrupting agents (EIAs) can cause interruption of thyroid and interrenals, resulting in physiologic compensatory mechanisms which can be adaptive, though such hormonal interactions are less recognized in fishes. The EIAs of physical, chemical and biological origins can specifically interrupt and modify the hormonal interactions between THs and cortisol, resulting in specific patterns of inter-hormonal interference. The physiologic analysis of these inter-hormonal interruptions during acclimation and post-acclimation to intrinsic or extrinsic EIAs reveals that combinations of anti-hormonal, pro-hormonal or stati-hormonal interference may help the fish to fine-tune their metabolic and osmotic performances as part of physiologic adaptation. This novel hypothesis on the phenomenon of inter-hormonal interference and its consequent physiologic interference during thyroid and interrenal interruption thus forms the basis of physiologic acclimation. This interfering action of TH and cortisol during hormonal interruption may subsequently promote ecological adaptation in fish as these physiologic processes ultimately favor them to survive in their hostile environment.

Characterization of vitellogenin gene expression in round goby (Neogobius melanostomus) using a quantitative polymerase chain reaction assay

A growing concern over endocrine disruption in aquatic species has prompted the development of molecular assays to monitor environmental impacts. This study describes the development of quantitative polymerase chain reaction (qPCR) assays to characterize the expression of two vitellogenin (Vtg) genes in the invasive round goby (Neogobius melanostomus). Fragments from the 18SrRNA (housekeeping gene), Vtg II, and Vtg III genes were cloned and sequenced. The qPCR assays were developed to detect hepatic Vtg expression in goby. The assays detected induction of both Vtg genes in nonreproductive males following a two-week laboratory exposure to 17β-estradiol (≥1 mg/kg i.p. injection). The assays were applied to goby from Hamilton Harbour, Lake Ontario (Canada), including those from sites where feminization and intersex of goby has been documented. Both Vtg genes had significantly higher expression in females compared to males. Male reproductive goby adopt either parental or sneaker tactics; Vtg II expression was higher in sneaker than in parental males but parental and nonreproductive males did not differ from each other. The Vtg III expression was significantly higher in sneaker males followed by parental males and nonreproductive males, respectively. The Vtg II and III expression in nonreproductive males was elevated in the contaminated site with documented intersex. This assay provides an important tool for the use of an invasive species in monitoring endocrine disruption in the Great Lakes region.

Short-term exposure to a synthetic estrogen disrupts mating dynamics in a pipefish

Sexual selection is responsible for the evolution of some of the most elaborate traits occurring in nature, many of which play a vital role in competition over access to mates and individual reproductive fitness. Because expression of these traits is typically regulated by sex-steroids there is a significant potential for their expression to be affected by the presence of certain pollutants, such as endocrine disrupting compounds. Endocrine disruptors have been shown to alter primary sexual traits and impact reproduction, but few studies have investigated how these compounds affect secondary sexual trait expression and how that may, in turn, impact mating dynamics. In this study we examine how short-term exposure to a synthetic estrogen impacts secondary sexual trait expression and mating dynamics in the Gulf pipefish, a species displaying sex-role reversal. Our results show that only 10days of exposure to 17α-ethinylestradiol results in adult male pipefish developing female-like secondary sexual traits. While these males are capable of reproduction, females discriminate against exposed males in mate choice trials. In natural populations, this type of discrimination would reduce male mating opportunities, thus potentially reducing their long-term reproductive success. Importantly, the effects of these compounds on mating dynamics and mating opportunity would not be observed using the current standard methods of assessing environmental contamination. However, disrupting these processes could have profound effects on the viability of exposed populations.

Multi-criteria decision analysis of test endpoints for detecting the effects of endocrine active substances in fish full life cycle tests

Fish full life cycle (FFLC) tests are increasingly required in the ecotoxicological assessment of endocrine active substances. However, FFLC tests have not been internationally standardized or validated, and it is currently unclear how such tests should best be designed to provide statistically sound and ecologically relevant results. This study describes how the technique of multi-criteria decision analysis (MCDA) was used to elicit the views of fish ecologists, aquatic ecotoxicologists and statisticians on optimal experimental designs for assessing the effects of endocrine active chemicals on fish. In MCDA qualitative criteria (that can be valued, but not quantified) and quantitative criteria can be used in a structured decision-making process. The aim of the present application of MCDA is to present a logical means of collating both data and expert opinions on the best way to focus FFLC tests on endocrine active substances. The analyses are presented to demonstrate how MCDA can be used in this context. Each of 3 workgroups focused on 1 of 3 species: fathead minnow (Pimephales promelas), Japanese medaka (Oryzias latipes), and zebrafish (Danio rerio). Test endpoints (e.g., fecundity, growth, gonadal histopathology) were scored for each species for various desirable features such as statistical power and ecological relevance, with the importance of these features determined by assigning weights to them, using a swing weighting procedure. The endpoint F1 fertilization success consistently emerged as a preferred option for all species. In addition, some endpoints scored highly in particular species, such as development of secondary sexual characteristics (fathead minnow) and sex ratio (zebrafish). Other endpoints such as hatching success ranked relatively highly and should be considered as useful endpoints to measure in tests with any of the fish species. MCDA also indicated relatively less preferred endpoints in fish life cycle tests. For example, intensive histopathology consistently ranked low, as did measurement of diagnostic biomarkers, such as vitellogenin, most likely due to the high costs of these methods or their limited ecological relevance. Life cycle tests typically do not focus on identifying toxic modes and/or mechanisms of action, but rather, single chemical concentration-response relationships for endpoints (e.g., survival, growth, reproduction) that can be translated into evaluation of risk. It is, therefore, likely to be an inefficient use of limited resources to measure these mechanism-specific endpoints in life cycle tests, unless the value of such endpoints for answering particular questions justifies their integration in specific case studies.

Measuring multiple hormones from a single water sample using enzyme immunoassays

Many aquatic species, such as teleosts, release into the water and detect multiple bioactive substances to assist in schooling, migration, alarm reactions, and to stimulate behavioral and physiological responses during reproduction and in parent-offspring interactions. Understanding the complex relationship between hormones, behavior and their function in communication requires the simultaneous examination of multiple circulating hormones. However, repeated blood sampling within a short time period is not possible in smaller animals without impacting the very behaviors under investigation. The non-invasive technique of collecting and measuring hormone values in holding water using either radioimmunoassay (RIA) or enzyme immunoassay (EIA) is becoming widely used in teleost research. Commercial assay kits in particular enable rapid and reliable data generation, yet their assay buffers are often specific and potentially incompatible with each other, which can hinder measuring multiple hormones from the same sample. We present here the validation and application of a "nested" elution technique we developed that allows for repeated sampling of multiple reproductive hormones - testosterone (T), 17beta-estradiol (E2), progesterone (P), prostaglandin F(2 alpha) (PGF) and 11-ketotestosterone (11KT) - from individual samples of animal holding water by using commercial EIA systems. Our results show that when using appropriate controls to account for possible technical and biological confounds, this technique provides a powerful new tool for research in aquatic endocrinology and physiology.

Endocrine disruption in aquatic vertebrates

Environmental compounds can interfere with endocrine systems of wildlife and humans. The main sink of such substances, called endocrine disrupters (ED), are surface waters. Thus, aquatic vertebrates, such as fish and amphibians, are most endangered. ED can adversely affect reproductive biology and the thyroid system. ED act by (anti)estrogenic and (anti)androgenic modes of action, resulting in abnormal sexual differentiation and impaired reproduction. These effects are mainly driven by direct interferences of ED with sex steroid receptors rather than indirectly by impacting synthesis and bioavailability of sex steroids, which in turn might affect the hypothalamic-pituitary-gonadal axis. Recent findings reveal that, in addition to the human-produced waste of ED, natural sources, such as parasites and decomposition of leaves, also might act as ED, markedly affecting sexual differentiation and reproduction in fish and amphibians. Although the thyroid system has essential functions in both fish and amphibians, amphibian metamorphosis has been introduced as the most sensitive model to detect thyroidal ED; no suitable fish model exists. Whereas ED may act primarily on only one specific endocrine target, all endocrine systems will eventually be deregulated as they are intimately connected to each other. The recent ecotoxicological issue of pharmaceutically active compounds (PhACs) present in the aquatic environment indicates a high potential for further endocrine modes of action on aquatic vertebrates by ED derived from PhACs, such as glucocorticoids, progestins, and beta-agonists.

Sexual reprogramming and estrogenic sensitization in wild fish exposed to ethinylestradiol

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.

Reproductive toxicity in Xenopus tropicalis after developmental exposure to environmental concentrations of ethynylestradiol

Reproductive disorders in wildlife and humans have been linked to developmental exposure to endocrine disrupting chemicals. In frog tadpoles, environmental concentrations of ethynylestradiol (EE(2)) disrupt gonadal differentiation which results in female-biased sex ratios at metamorphosis indicating sex-reversal of genotypic males. It is not known if developmental exposure to estrogens results in reduced reproductive success in amphibians. The objective of this work was to investigate if exposure to environmentally relevant concentrations of EE(2) during sex differentiation impairs reproductive organ development, fertility, and sexual behavior in adult frogs. A specific aim was to evaluate if testicular structure and function was affected in males that were not sex-reversed. Xenopus tropicalis tadpoles were exposed until metamorphosis to 6, 60, and 600 pM EE(2). Eight months after metamorphosis, reproductive organ morphology and fertility were evaluated. Larval EE(2)-exposure caused an increased proportion of phenotypic females indicating that sex-reversal of genotypic males is persistent. Sex-reversal was implied at concentrations as low as 6 pM (1.8 ng/l), which is comparable to levels observed in the environment. EE(2)-exposed males that were not sex-reversed had a significantly reduced fertilization rate compared with control males. Histological evaluation revealed that EE(2)-exposed males had a reduced amount of spermatozoa in the testis. Among frogs with ovaries there was a significantly higher percentage that lacked oviducts in the group exposed to 600 pM EE(2) compared with control females. No effect of EE(2) on sexual behavior was noted. The results indicate that reproduction in wild frogs might be impaired by estrogenic environmental pollutants. Similarities between the present effects and those reported in fish, birds and mammals after developmental exposure to estrogens suggest that X. tropicalis is a promising animal model for research on developmental reproductive toxicity.

Lack of a heritable reproductive defect in the offspring of male rainbow trout exposed to the environmental estrogen 17alpha-ethynylestradiol

Endocrine disruptors, including environmental estrogens, have been shown to induce heritable effects through both genetic and epigenetic mechanisms in mammals. Despite this information and the wealth of knowledge regarding the significant reproductive impacts endocrine disruptors impose on fishes, no studies have reported whether the observed effects are heritable. Without this information it is difficult to establish the long-term consequences for exposed populations. To determine potential consequences of long-term effects we must consider the possibility that induced reproductive defects in fishes may be heritable. Using rainbow trout (Oncorhynchus mykiss) as a model this study aims to determine whether a specific reproductive defect observed in 17alpha-ethynylestradiol exposed male parents, diminished progeny survival, is heritable in the unexposed surviving F1 males. Semen was collected from anesthetized males of the F1 generation upon sexual maturation at two time-points, one year old precocious males and two years old males. In vitro fertilization was used to produce an F2 generation. F2 embryos were then analyzed for survival at 19 days post-fertilization (eye pigmentation) and the different treatment groups statistically compared to the controls. Analysis indicated that F2 offspring survival from F1 males propagated from both exposed and unexposed parents survive normally and no heritable effect was observed in males from the F1 generation for this specific reproductive defect. These results provide scope for the recovery of fish populations exposed to environmental estrogens should the contaminant be removed.

Aneuploid sperm formation in rainbow trout exposed to the environmental estrogen 17{alpha}-ethynylestradiol

Environmental contaminants that mimic native estrogens (i.e., environmental estrogens) are known to significantly impact a wide range of vertebrate species and have been implicated as a source for increasing human male reproductive deficiencies and diseases. Despite the widespread occurrence of environmental estrogens and recognized detrimental effects on male vertebrate reproduction, no specific mechanism has been determined indicating how reduced fertility and/or fecundity is achieved. Previous studies show that male rainbow trout, Oncorhynchus mykiss, exposed to the environmental estrogen 17alpha-ethynylestradiol (EE2) before gamete formation and fertilization produce progeny with significantly reduced embryonic survival. To determine whether this observed decrease results from sperm chromosome alterations during spermatogenesis, male rainbow trout were exposed to 10 ng of EE2/l for 50 days. After exposure, semen was collected and sperm aneuploidy levels analyzed with two chromosome markers by fluorescent in situ hybridization. In vitro fertilizations were also conducted by using control and exposed sperm crossed to eggs from an unexposed female for offspring analysis. Evaluations for nucleolar organizer region number and karyotype were performed on developing embryos to determine whether sperm aneuploidy translated into embryonic aneuploidy. Results conclusively show increased aneuploid sperm formation due to EE2 exposure. Additionally, embryonic cells from propagated progeny of individuals possessing elevated sperm aneuploidy display high levels of embryonic aneuploidy. This study concludes that EE2 exposure in sexually developing male rainbow trout increases levels of aneuploid sperm, providing a mechanism for decreased embryonic survival and ultimately diminished reproductive success in EE2 exposed males.

Molecular biomarkers of endocrine disruption in small model fish

A wide range of environmental contaminants can interfere with hormonal regulation in vertebrates. These endocrine disrupting chemicals (EDCs) are of high relevance for human and wildlife health, since endocrine signalling controls many essential physiological processes which impact on the individual's health, such as growth and development, stress response, and ultimately reproduction and population development. Small fish represent a cost-effective model for testing potential EDCs allowing the possibility to integrate from molecular to phenotypic and functional effects. We have comprehensively reviewed exposure-effect data from four different small model fish: zebrafish, medaka, fathead minnow, and the three-spined stickleback. The majority of available data refer to EDCs interfering with reproductive hormones. However, we have also included interactions with other hormone systems, particularly the thyroid hormones. We demonstrate that the available data clearly indicates the predictive potential of molecular biomarkers, supporting the development and regulatory application of simple molecular-based screening assays using small model fish for EDC testing.