Skeletal morphology and maturation of male Gambusia holbrooki exposed to sewage treatment plant effluent

Physiological and transcriptional effects in the male western mosquitofish (Gambusia affinis) following exposure to dexamethasone

Dexamethasone (DEX) is a synthetic glucocorticoid widely found in a variety of aquatic environments and has potential adverse effects on aquatic organisms. This study was to assess the toxic effects of exposure to different concentrations (0, 5 and 50 μg/L) of DEX for 60 days on adult male mosquitofish (Gambusia affinis). Morphological analyses of skeleton and anal fin, histological effects of testes and livers, and transcriptional expression levels of genes related to reproductive and immune system were determined. The results showed that exposure to DEX significantly increased 14L and 14D values of hemal spines, which suggested DEX could affect skeleton development and result in more masculine characteristics in male fish. In addition, the damage to testis and liver tissue was observed after DEX treatment. It also enhanced mRNA expression of Erβ gene in the brain and Hsd11b1 gene in the testis. The findings of this study reveal physiological and transcriptional effects of DEX on male mosquitofish.

Endocrine disrupting effects in western mosquitofish Gambusia affinis in two rivers impacted by untreated rural domestic wastewaters

Domestic wastewaters are an important source of endocrine disrupting chemicals in the receiving aquatic environment. Most rural domestic wastewaters (RDWs) in China have been directly discharged into the aquatic environment without any treatment. Here we studied the effects of RDWs on the western mosquitofish (Gambusia affinis) from two rural rivers receiving untreated RDWs. Mosquitofish samples were collected at 5 sampling sites along two rivers during dry and wet seasons. Sex ratios, secondary sex characteristics and transcriptional levels of target genes related to the endocrine system in adult females and males were determined. In parallel, various pollutants including steroid hormones, phenolic compounds, pesticides, polycyclic aromatic hydrocarbons (PAHs) and heavy metals were measured in the water samples at all sites. The results showed that the androgenic effects in the fish were evidenced by significant increase in male to female ratio in fish populations at two sampling sites and by the presence of modified hemal spines in females at four sampling sites when compared to the reference site. The males from the two rivers had increased Vtg mRNA expressions with a maximal 6.2-fold increase relative to the reference site and a delayed development of hemal spines. The redundancy analysis (RDA) showed that some physiological parameters were related to steroid hormones, phenolic compounds and PAHs. The findings from this study suggest that RDWs can lead to masculinization in females and feminization in males.

Histopathology, vitellogenin and chemical body burden in mosquitofish (Gambusia holbrooki) sampled from six river sites receiving a gradient of stressors

There are over 40,000 chemical compounds registered for use in Australia, and only a handful are monitored in the aquatic receiving environments. Their effects on fish species in Australia are largely unknown. Mosquitofish (Gambusia holbrooki) were sampled from six river sites in Southeast Queensland identified as at risk from a range of pollutants. The sites selected were downstream of a wastewater treatment plant discharge, a landfill, two agricultural areas, and two sites in undeveloped reaches within or downstream of protected lands (national parks). Vitellogenin analysis, histopathology of liver, kidney and gonads, morphology of the gonopodium, and chemical body burden were measured to characterize fish health. Concentrations of trace organic contaminants (TrOCs) in water were analyzed by in vitro bioassays and chemical analysis. Estrogenic, anti-estrogenic, anti-androgenic, progestagenic and anti-progestagenic activities and TrOCs were detected in multiple water samples. Several active pharmaceutical ingredients (APIs), industrial compounds, pesticides and other endocrine active compounds were detected in fish carcasses at all sites, ranging from <4-4700ng/g wet weight, including the two undeveloped sites. While vitellogenin protein was slightly increased in fish from two of the six sites, the presence of micropollutants did not cause overt sexual endocrine disruption in mosquitofish (i.e., no abnormal gonads or gonopodia). A correlation between lipid accumulation in the liver with total body burden warrants further investigation to determine if exposure to low concentrations of TrOCs can affect fish health and increase stress on organs such as the liver and kidneys via other mechanisms, including disruption of non-sexual endocrine axes involved in lipid regulation and metabolism.

Physiological responses and gene expression changes in the western mosquitofish (Gambusia affinis) exposed to progesterone at environmentally relevant concentrations

Progesterone (P4) is a natural and synthetic steroid, widely distributed in the aquatic environments. It can lead to adverse effects on the endocrine system in aquatic organisms. This study investigated the toxicological effects of exposure to environmentally relevant concentrations (4, 44, and 410ng/L) of progesterone for 42 d on adult female mosquitofish, Gambusia affinis. We performed morphological and histological analyses on gonads, anal fins, liver, and gills after the exposure of mosquito fish to P4. The expression levels of genes (vtg, er, and ar isoforms) related to fish reproduction and detoxification (cyp1a) in the liver were quantified by quantitative real-time polymerase chain reaction. The results showed that the progesterone exposure induced slight masculinization in female mosquitofish, influenced the oocyte maturation as revealed by histology of the ovaries, and caused severe damages to the liver and gills of adult female mosquitofish. It also suppressed the mRNAs expression of vtg, er, cyp1a, and significantly enhanced the expression of ar mRNA in the liver. This study reveals the molecular and physiological effects of progesterone at environmentally relevant concentrations, which might further be translated to alterations in the reproduction of mosquitofish.

No evidence of exposure to environmental estrogens in two feral fish species sampled from the Yarra River, Australia: A comparison with Northern Hemisphere studies

Environmental estrogens originate from a variety of sources including sewage treatment plant (STP) effluents and adverse physiological effects (endocrine disruption) have been observed in several fish species sampled downstream of STP discharges. In this study we examined common carp (Cyprinus carpio) and roach (Rutilis rutilis) for signs of exposure to environmental estrogens in the iconic Yarra River, Melbourne, Australia. The Yarra River flows through the city of Melbourne and more than 2 million people live within the catchment. Two STPs discharge water into the Yarra River within the middle reaches, and the areas immediately downstream of these discharge locations were the focus of this study. Carp and roach were chosen as test species since both have been utilised extensively for endocrine disruption research throughout Europe, North America and Asia, and data from various international studies was used for comparison with the results of the present study. Neither species showed evidence of exposure to environmental estrogens, with no elevation of plasma vitellogenin levels in males and no incidence of intersex gonads. Most physiological endpoints in both species from this study were within ranges reported in carp and roach from reference sites in other studies, however some degenerative histological changes in both male and female gonads were observed. Surface water samples showed no estrogenic activity (measured by the yeast-estrogen screen, YES), but did display strong anti-estrogenic and weak androgenic activity (measured by the yeast-androgen screen, YAS). Whilst the results show no evidence of impacts from environmental estrogens in the Yarra River, the presence of both anti-estrogenic and androgenic activity in water samples, as well as some gonadal changes in carp is concerning and indicates that our focus needs to broaden, in order to look for biological impacts in resident fauna that might be due to environmental pollutants other than environmental estrogens.

Integrated assessment of wastewater treatment plant effluent estrogenicity in the Upper Murray River, Australia, using the native Murray rainbowfish (Melanotaenia fluviatilis)

The contamination of major continental river systems by endocrine-active chemicals (EACs) derived from the discharge of wastewater treatment plant (WWTP) effluents can affect human and ecosystem health. As part of a long-term effort to develop a native fish model organism for assessment of endocrine disruption in Australia's largest watershed, the Murray-Darling River Basin, the present study evaluated endocrine disruption in adult males of the native Australian Murray rainbowfish (Melanotaenia fluviatilis) exposed to effluent from an activated sludge WWTP and water from the Murray River during a 28-d, continuous-flow, on-site experiment. Analysis of the WWTP effluent and river water detected estrone and 17β-estradiol at concentrations up to approximately 25 ng L(-1) . Anti-estrogenicity of effluent samples was detected in vitro using yeast-based bioassays (yeast estrogen screen) throughout the experiment, but estrogenicity was limited to the first week of the experiment. Histological evaluation of the testes indicated significant suppression of spermatogenesis by WWTP effluent after 28 d of exposure. Plasma vitellogenin concentrations and expression of vitellogenin messenger RNA in liver were not significantly affected by exposure to WWTP effluent. The combination of low contaminant concentrations in the WWTP effluent, limited endocrine disrupting effects in the Murray rainbowfish, and high in-stream dilution factors (>99%) suggest minimal endocrine disruption impacts on native Australian fish in the Murray River downstream from the WWTP outfall.

Effects of estrogens and estrogenic disrupting compounds on fish mineralized tissues

Estrogens play well-recognized roles in reproduction across vertebrates, but also intervene in a wide range of other physiological processes, including mineral homeostasis. Classical actions are triggered when estrogens bind and activate intracellular estrogen receptors (ERs), regulating the transcription of responsive genes, but rapid non-genomic actions initiated by binding to plasma membrane receptors were recently described. A wide range of structurally diverse compounds from natural and anthropogenic sources have been shown to interact with and disrupt the normal functions of the estrogen system, and fish are particularly vulnerable to endocrine disruption, as these compounds are frequently discharged or run-off into waterways. The effect of estrogen disruptors in fish has mainly been assessed in relation to reproductive endpoints, and relatively little attention has been given to other disruptive actions. This review will overview the actions of estrogens in fish, including ER isoforms, their expression, structure and mechanisms of action. The estrogen functions will be considered in relation to mineral homeostasis and actions on mineralized tissues. The impact of estrogenic endocrine disrupting compounds on fish mineralized tissues will be reviewed, and the potential adverse outcomes of exposure to such compounds will be discussed. Current lacunae in knowledge are highlighted along with future research priorities.

Modeling of steroid estrogen contamination in UK and South Australian rivers predicts modest increases in concentrations in the future

The prediction of risks posed by pharmaceuticals and personal care products in the aquatic environment now and in the future is one of the top 20 research questions regarding these contaminants following growing concern for their biological effects on fish and other animals. To this end it is important that areas experiencing the greatest risk are identified, particularly in countries experiencing water stress, where dilution of pollutants entering river networks is more limited. This study is the first to use hydrological models to estimate concentrations of pharmaceutical and natural steroid estrogens in a water stressed catchment in South Australia alongside a UK catchment and to forecast their concentrations in 2050 based on demographic and climate change predictions. The results show that despite their differing climates and demographics, modeled concentrations of steroid estrogens in effluents from Australian sewage treatment works and a receiving river were predicted (simulated) to be similar to those observed in the UK and Europe, exceeding the combined estradiol equivalent's predicted no effect concentration for feminization in wild fish. Furthermore, by 2050 a moderate increase in estrogenic contamination and the potential risk to wildlife was predicted with up to a 2-fold rise in concentrations.

Estrogenic and androgenic effects in mosquitofish (Gambusia affinis) from streams contaminated by municipal effluent in Guangzhou, China

The study reported in this paper used mosquitofish to investigate the estrogenic and androgenic effects of municipal wastewater contamination on the stream system in Guangzhou, China. Western mosquitofish collected from a reference site and five study sites in streams forming part of the Pearl River network were dissected and analyzed for their morphological characteristics (anal fin and hemal spine characteristics) and target mRNA expression of genes (VTGα and ERα mRNA expression). Increased VTGα mRNA expression in males and decreased VTGα mRNA expression in females were observed in samples taken from four of the five study sites, with no such observations being made at the reference site. Correlation analysis indicated a significant correlation between the hemal spine morphology index and the gene transcription relative to the reference site. The multiple index also indicated that both male and female mosquitofish in contaminated streams were altered by discharged wastewater, as reflected in their morphological changes and relative induction of mRNA expression of genes in comparison to fish collected from the reference site.

Vitellogenin induction by 17β-estradiol and 17α-ethynylestradiol in male Murray rainbowfish (Melanotaenia fluviatilis)

Hepatic vitellogenin (VTG) mRNA and plasma protein assays were developed for the Murray rainbowfish (Melanotaenia fluviatilis), a native freshwater fish species in Australia. Adult male Murray rainbowfish were exposed to 17β-estradiol (E2) or 17α-ethynylestradiol (EE2) at 0, 1, 5, 10, 50, or 100 ng/L in a semistatic system for 7 d. Vitellogenin mRNA was quantified by quantitative polymerase chain reaction, and VTG protein was semiquantified in plasma using an enzyme-linked immunosorbent assay. Water concentrations were quantified by liquid chromatography coupled with tandem mass spectrometry and were on average 110% and 85% nominal concentrations for E2 and EE2, respectively. Vitellogenin transcripts and protein were upregulated in male Murray rainbowfish exposed to either E2 or EE2 in a dose-responsive manner, with calculated 10% effective concentration (EC10) values for E2 of 3.71 ng/L and 11.6 ng/L for VTG mRNA and protein, respectively, and for EE2 of 2.77 ng/L and 8.47 ng/L for VTG mRNA and protein, respectively. Comparisons of these responses with responses of commonly used test species, including zebrafish (Danio rerio), fathead minnow (Pimephales promelas), and Japanese medaka (Oryzias latipes), revealed the Murray rainbowfish to be a sensitive test species for estrogenic effects via the estrogen receptor pathway. The present study suggests that the Murray rainbowfish would be a suitable candidate for future field studies designed for assessing estrogenic effects of effluent discharges in the Australian freshwater environment.

Developmental and reproductive characteristics of western mosquitofish (Gambusia affinis) exposed to paper mill effluent in the Dengcun River, Sihui, South China

The study reported in this paper tested the hypothesis that the developmental and reproductive health of mosquitofish (Gambusia affinis) exposed to pulp and paper effluent in the Dengcun River would differ from that of mosquitofish living in a reference site. We also studied whether morphological characteristics such as the anal fin and hemal spines of mosquitofish could serve as indicators for evaluating the androgenic effect and mosquitofish population security in the Dengcun River. Male and female mosquitofish were captured at three sites contaminated by pulp and paper effluent in the Dengcun River in Sihui, South China, and at a nearby uncontaminated reference site. Samples were collected from the sampling sites on the same day in August 2009. We compared the populations by total length, wet body and liver mass, gonad mass, and population composition. We also compared the populations according to number of anal fin segments, oocyte and embryo count, anal fin and hemal spine morphology among females, and by sperm count and viability among males, and observed the gonadal and liver histology of both males and females. Female mosquitofish exposed to pulp and paper effluent in the Dengcun River were generally smaller in length and mass, had a greater number of anal fin segments and more embryos, but had significantly fewer oocytes in comparison with those living at the reference site. The higher number of anal fin ray 3 segments and the increased ray 4:6 length ratio observed among fish taken from the Dengcun River sites indicated that they might be subject to the androgenic effect. Furthermore, the significantly different hemal spine morphology of the effluent-affected females also indicated the pulp and paper mills effluents in Dengcun River might contain androgenic substance(s). Male mosquitofish at the sites exposed to effluent had a higher number of anal fin segments and greater testis mass in comparison with those living at the reference site. No evidence of intersex was found in either males or females, although histopathological tests on females revealed histologic abnormalities in the liver and gonads. It can be concluded that pulp and paper effluent contamination in the Dengcun River has affected a number of developmental parameters and reproductive characteristics in mosquitofish, with possible adverse effects on reproduction in this population.

Altered development and reproduction in western mosquitofish (Gambusia affinis) found in the Hanxi River, southern China

The current study investigated the development and reproductive health of western mosquitofish (Gambusia affinis) in the Hanxi River, which has been heavily contaminated by municipal wastewaters from towns in Dongguan of southern China. Western mosquitofish collected from four study sites, Songmu (SM), Yangwu (YW), Hengli (HL), and Zhangcun (ZC) of the Hanxi River, as well as a reference site (LX) of the Liuxi River, were dissected and analyzed for development parameters (total length, wet body mass, liver mass, gonad index, and population composition), reproductive parameters (oocyte count and weight of females, and sperm count and viability of males), and morphology (anal fin in males and females, and hemal spines in males). With the exception of the origin site (SM), mosquitofish from the Hanxi River exhibited significantly decreasing development and reproduction levels. Significant correlations were found for the collected mosquitofish between the morphological and reproductive indexes (ratio of perpendicular distance to tip to vertical distance from the tip on the 16th hemal spine) versus the sperm count of males; ratio 16P:16D versus sperm viability of males; segments of anal fin ray 3 versus oocyte count of females; and segments of anal fin ray 3 versus average oocyte mass of females. The results demonstrated that both male and female mosquitofish in the Hanxi River were affected by the discharged wastewaters, as reflected in their morphological changes in comparison with those of mosquitofish from the reference site.

Bioactivity of POPs and their effects in mosquitofish in Sydney Olympic Park, Australia

The site of the 2000 Olympic Games (Sydney Olympic Park (SOP), Sydney, Australia) was contaminated by persistent organic pollutants (POPs) prior to remediation in the 1990s. This study investigates the bioactivity of POPs in the sediment and water of wetlands across SOP by in vitro 2,3,7,8-TCDD equivalence (TCDDeq) measurement (H4IIE cell line bioassay). Further, it examines whether disturbance of these sediments is likely to mobilise ligands for this receptor into the water column. Exposure to aryl hydrocarbon receptor (AhR) ligands was measured in vivo using hepatic cytochrome P4501A (CYP1A) induction (EROD) in the mosquitofish (Gambusia holbrooki). Aqueous TCDDeq ranged from 0.013 to 0.057 pM in SOP wetlands which was significantly (p<0.05) less that in urban reference sites. These concentrations were not correlated to physical or chemical characteristics of the wetlands. In the sediments, TCDDeq ranged from 0.0016 to 7.06 microg/kg and these were not significantly (p>or=0.05) different to that measured in urban reference sites. Simulated disturbance of small quantities of sediment in water samples significantly (p<0.05) increased the levels of TCDDeq measured in the water. Sediment TCDDeq was correlated to sediment SigmaPAH concentration in 2006 and sediment SigmaPCB, SigmaDDT concentrations and fine sediment grain size in 2005. While fish at one SOP wetland had hepatic EROD activity elevated above the estimated basal level for this species, these were at the lower end of the range measured in urban impacted, non-remediated wetlands. EROD activity was positively correlated with both the sediment SigmaPCB load and aqueous TCDDeq. Increased catchment size was correlated with increased EROD activity suggesting an even spread of POPs throughout the residential areas of the Sydney metropolitan area. The concentration of bioactive POPs in the wetlands of SOP is therefore low relative to urban reference sites demonstrating the ongoing success of the remediation program.