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At least 37 records · Page 2Linked to original sources
USGS2010

Annual sex steroid and other physiological profiles of Pacific lampreys ( Entosphenus tridentatus )

We documented changes in plasma levels of estradiol 17-β (E2), progesterone (P), 15α-hydroxytestosterone (15α-T), thyroxine (T4), triiodothyronine (T3), protein, triglycerides (TGs), and glucose in adult Pacific lampreys ( Entosphenus tridentatus ) held in the laboratory in two different years. Levels of E2 in both sexes ranged from 0.5 to 2 ng/mL from September to March, peaked in late April (2–4 ng/mL), and decreased in May, with levels higher in males than in females. Levels of P were low from September through April, but then increased substantially during May (2–4 ng/mL), with levels again highest in males. Levels of 15α-T in males were around 0.75 ng/mL through the winter before exceeding 1 ng/mL in April and decreasing thereafter, whereas females showed a gradual increase from 0.25 ng/mL in November to 0.5 ng/mL in April before decreasing. Thyroxine concentrations differed between fish in each year, with most having levels ranging from 0.75 to 2.5 ng/mL in the fall and winter, and only fish in 2003 showing distinct peaks (3–4 ng/mL) in early April or May. Plasma T3 was undetectable from November through mid-March before surging dramatically in April (ca. 150 ng/mL) and decreasing thereafter. Levels of protein, TGs, and glucose decreased or were stable during the fall and winter with TGs and glucose surging in late April to early May for some fish. Our study is the first to document long-term physiological changes in Pacific lampreys during overwintering and sexual maturation and increases our understanding of the life history of this unique fish.

Comparative Biochemistry and Physiology, Part A: M↗
USGS2026

Characterizing the annual cycle of steroid hormones in males from an invasive vertebrate (Python bivittatus) of management concern

South Florida's subtropical climate has facilitated the establishment of numerous invasive species, including the Burmese python ( Python bivittatus ). Despite decades of efforts to manage the invasive python population across South Florida, we lack a comprehensive understanding of their reproductive physiology, limiting the development of targeted control strategies. Here, we characterized seasonal patterns of testosterone (T) and corticosterone (CORT) in free-ranging adult male pythons and evaluated environmental correlates of hormone variation. Results indicate that T peaks before the onset of the breeding season and declines through the season to baseline levels in the non-breeding season. CORT did not show a clear seasonal trend but showed greater variability during the breeding season. These findings reveal that photoperiod and ambient temperature are key environmental correlates of male hormone cycles, contributing to our understanding of the endocrine phenology of a tropical ectotherm in a novel environment.

Florida↗
USGS2011

Biodegradation and attenuation of steroidal hormones and alkylphenols by stream biofilms and sediments

Biodegradation of select endocrine-disrupting compounds (17&beta;-estradiol, estrone, 17&alpha;-ethynylestradiol, 4-nonylphenol, 4-nonylphenolmonoexthoylate, and 4-nonylphenoldiethoxylate) was evaluated in stream biofilm, sediment, and water matrices collected from locations upstream and downstream from a wastewater treatment plant effluent discharge. Both biologically mediated transformation to intermediate metabolites and biologically mediated mineralization were evaluated in separate time interval experiments. Initial time intervals (0&ndash;7 d) evaluated biodegradation by the microbial community dominant at the time of sampling. Later time intervals (70 and 185 d) evaluated the biodegradation potential as the microbial community adapted to the absence of outside energy sources. The sediment matrix was more effective than the biofilm and water matrices at biodegrading 4-nonylphenol and 17&beta;-estradiol. Biodegradation by the sediment matrix of 17&alpha;-ethynylestradiol occurred at later time intervals (70 and 185 d) and was not observed in the biofilm or water matrices. Stream biofilms play an important role in the attenuation of endocrine-disrupting compounds in surface waters due to both biodegradation and sorption processes. Because sorption to stream biofilms and bed sediments occurs on a faster temporal scale (<1 h) than the potential to biodegrade the target compounds (50% mineralization at >185 d), these compounds can accumulate in stream biofilms and sediments.

Environmental Science & Technology↗
USGS1977

Reproductive steroids in the white-tailed deer (Odocoileus virginianus borealis). I. Seasonal changes in the female

A total of 161 blood samples collected from 77 white-tailed does ( Odocoileus virginianus borealis ) during the years 1971 through 1974 in Minnesota were utilized to make a preliminary characterization of the estrogen and progesterone levels in pregnant and nonpregnant animals. Progesterone and estrogen were measured by radioimmunoassay. Progesterone levels during the months of December through February were similar for pregnant and nonpregnant animals (3.98 ± 0.57 vs. 5.50 ± 0.82 ng/ml, x̄ ± S.E., N.S., t = 1.51). The pregnant animals had higher progesterone levels during the March through May period (4.61 ± 0.44 vs. 1.94 ± 0.85, P<0.01). Progesterone levels during the months of June to early November, i.e., anestrus, were low and similar for lactating and nonlactating animals. Estrogen levels did not change during the year except for the period just before parturition in the pregnant does when estrogen levels were dramatically elevated (178 ± 29 pg/ml). Two nonpregnant adult does were sampled every 5 days from late January through early March. Progesterone levels exhibited a cyclic pattern of about 28 days duration. Estrogen levels showed no distinct pattern but tended to be inversely related to progesterone. These data suggest that 1) deer exhibit estrous cycles of about 25 to 30 days in length, 2) that estrous cycles recurred in nonpregnant does from November through early March, 3) that progesterone levels are similar for pregnancy and the luteal phase of the estrous cycle and 4) that late pregnancy is characterized by high estrogen levels as compared to early pregnancy and the estrous cycle.

Minnesota↗
USGS2022

Testing whether adrenal steroids mediate phenotypic and physiologic effects of elevated salinity on larval tiger salamanders

Salinity (sodium chloride, NaCl) from anthropogenic sources is a persistent contaminant that negatively affects freshwater taxa. Amphibians can be susceptible to salinity, but some species are innately or adaptively tolerant. Physiological mechanisms mediating tolerance to salinity are still unclear, but changes in osmoregulatory hormones such as corticosterone (CORT) and aldosterone (ALDO) are prime candidates. We exposed larval barred tiger salamanders ( Ambystoma mavortium ) to environmentally relevant NaCl treatments (<32–4000 mg·L −1 ) for 24 days to test effects on growth, survival, and waterborne CORT responses. Of those sampled, we also quantified waterborne ALDO from a subset. Using a glucocorticoid antagonist (RU486), we also experimentally suppressed CORT signaling of some larvae to determine if CORT mediates effects of salinity. There were no strong differences in survival among salinity treatments, but salinity reduced dry mass, snout–vent length, and body condition while increasing water content of larvae. High survival and sublethal effects demonstrated that salamanders were physiologically challenged but could tolerate the experimental concentrations. CORT signaling did not attenuate sublethal effects of salinity. Baseline and stress-induced (after an acute stressor, shaking) CORT were not influenced by salinity. ALDO was correlated with baseline CORT, suggesting it could be difficult to decouple the roles of CORT and ALDO. Future studies comparing ALDO and CORT responses of adaptively tolerant and previously unexposed populations could be beneficial to understand the roles of these hormones in tolerance to salinity. Nevertheless, our study enhances our understanding of the roles of corticosteroid hormones in mediating effects of a prominent anthropogenic stressor.

Integrative Zoology↗
USGS1991

Effects of orally administered steroids on lake trout and Atlantic salmon

Lake trout ( Salvelinus namaycush ) and Atlantic salmon ( Salmo salar ) fed 30 mg β‐estradiol/kg of feed for 100 d from first feeding had liver and kidney pathology similar to but much less severe than that previously reported for rainbow trout ( Oncorhynchus mykiss ). Mortality was not affected. Both lake trout and Atlantic salmon treated with estradiol weighed significantly less than control fish at the end of the treatment period and at 200 d posttreatment. Testosterone‐treated fish of both species weighed less than control fish at the end of the treatment period. By day 200 posttreatment, testosterone‐treated and untreated lake trout weighed the same, but testosterone‐treated Atlantic salmon were heavier than control fish. Estradiol treatment produced an all‐female population of Atlantic salmon but not of lake trout. Testosterone at 5 mg/kg feed increased the ratio of males to females in both species.

Progressive Fish-Culturist↗
USGS1983

Feminization of channel catfish by oral administration of steroid sex hormones

Oral administration of 17‐β‐estradiol or 17‐α‐ethynyltestosterone to sexually undifferentiated channel catfish Ictaturus punctatus during the first 21 days after yolk‐sac absorption resulted in the production of 100% females. The androgen was effective at doses of 6 to 600 μg/g of feed, but not at 0.6 μg/g.

Transactions of the American Fisheries Society↗
USGS2008

Apparent tolerance of turkey vultures (Cathartes aura) to the non-steroidal anti-inflammatory drug diclofenac

The nonsteroidal anti‐inflammatory drug diclofenac is extremely toxic to Old World Gyps vultures (median lethal dose ∼0.1–0.2 mg/kg), evoking visceral gout, renal necrosis, and mortality within a few days of exposure. Unintentional secondary poisoning of vultures that fed upon carcasses of diclofenac‐treated livestock decimated populations in the Indian subcontinent. Because of the widespread use of diclofenac and other cyclooxygenase‐2 inhibiting drugs, a toxicological study was undertaken in turkey vultures ( Cathartes aura ) as an initial step in examining sensitivity of New World scavenging birds. Two trials were conducted entailing oral gavage of diclofenac at doses ranging from 0.08 to 25 mg/kg body weight. Birds were observed for 7 d, blood samples were collected for plasma chemistry (predose and 12, 24, and 48 h and 7 d postdose), and select individuals were necropsied. Diclofenac failed to evoke overt signs of toxicity, visceral gout, renal necrosis, or elevate plasma uric acid at concentrations greater than 100 times the estimated median lethal dose reported for Gyps vultures. For turkey vultures receiving 8 or 25 mg/kg, the plasma half‐life of diclofenac was estimated to be 6 h, and it was apparently cleared after several days as no residues were detectable in liver or kidney at necropsy. Differential sensitivity among avian species is a hallmark of cyclooxygenase‐2 inhibitors, and despite the tolerance of turkey vultures to diclofenac, additional studies in related scavenging species seem warranted.

Environmental Toxicology and Chemistry↗
USGS2001

Neuroendocrine and behavioral implications of endocrine disrupting chemicals in quail

Studies in our laboratory have focused on endocrine, neuroendocrine, and behavioral components of reproduction in the Japanese quail. These studies considered various stages in the life cycle, including embryonic development, sexual maturation, adult reproductive function, and aging. A major focus of our research has been the role of neuroendocrine systems that appear to synchronize both endocrine and behavioral responses. These studies provide the basis for our more recent research on the impact of endocrine disrupting chemicals (EDCs) on reproductive function in the Japanese quail. These endocrine active chemicals include pesticides, herbicides, industrial products, and plant phytoestrogens. Many of these chemicals appear to mimic vertebrate steroids, often by interacting with steroid receptors. However, most EDCs have relatively weak biological activity compared to native steroid hormones. Therefore, it becomes important to understand the mode and mechanism of action of classes of these chemicals and sensitive stages in the life history of various species. Precocial birds, such as the Japanese quail, are likely to be sensitive to EDC effects during embryonic development, because sexual differentiation occurs during this period. Accordingly, adult quail may be less impacted by EDC exposure. Because there are a great many data available on normal development and reproductive function in this species, the Japanese quail provides an excellent model for examining the effects of EDCs. Thus, we have begun studies using a Japanese quail model system to study the effects of EDCs on reproductive endocrine and behavioral responses. In this review, we have two goals: first, to provide a summary of reproductive development and sexual differentiation in intact Japanese quail embryos, including ontogenetic patterns in steroid hormones in the embryonic and maturing quail. Second, we discuss some recent data from experiments in our laboratory in which EDCs have been tested in Japanese quail. The Japanese quail provides an excellent avian model for testing EDCs because this species has well-characterized reproductive endocrine and behavioral responses. Considerable research has been conducted in quail in which the effects of embryonic steroid exposure have been studied relative to reproductive behavior. Moreover, developmental processes have been studied extensively and include investigations of the reproductive axis, thyroid system, and stress and immune responses. We have conducted a number of studies, which have considered long-term neuroendocrine consequences as well as behavioral responses to steroids. Some of these studies have specifically tested the effects of embryonic steroid exposure on later reproductive function in a multigenerational context. A multigenerational exposure provides a basis for understanding potential exposure scenarios in the field. In addition, potential routes of exposure to EDCs for avian species are being considered, as well as differential effects due to stage of the life cycle at exposure to an EDC. The studies in our laboratory have used both diet and egg injection as modes of exposure for Japanese quail. In this way, birds were exposed to a specific dose of an EDC at a selected stage in development by injection. Alternatively, dietary exposure appears to be a primary route of exposure; therefore experimental exposure through the diet mimics potential field situations. Thus, experiments should consider a number of aspects of exposure when attempting to replicate field exposures to EDCs.

Hormones and Behavior↗
USGS2013

Regulation of a putative corticosteroid, 17, 21-dihydroxypregn-4-ene, 3, 20-one, in sea lamprey, Petromyzon marinus

In higher vertebrates, in response to stress, the hypothalamus produces corticotropin-releasing hormone (CRH), which stimulates cells in the anterior pituitary to produce adrenocorticotropic hormone (ACTH), which in turn stimulates production of either cortisol (F) or corticosterone (B) by the adrenal tissues. In lampreys, however, neither of these steroids is present. Instead, it has been proposed that the stress steroid is actually 17,21-dihydroxypregn-4-ene-3,20-dione (11-deoxycortisol; S). However, there have been no studies yet to determine its mechanism of regulation or site of production. Here we demonstrate that (1) intraperitoneal injections of lamprey-CRH increase plasma S in a dose dependent manner, (2) intraperitoneal injections of four lamprey-specific ACTH peptides at 100 lg/kg, did not induce changes in plasma S concentrations in either males or females; (3) two lamprey-specific gonadotropin-releasing hormones (GnRH I and III) and arginine-vasotocin (AVT), all at single doses, stimulated S production as well as, or to an even greater extent than CRH; (4) sea lamprey mesonephric kidneys, in vitro, converted tritiated 17a-hydroxyprogesterone (17a-P) into a steroid that had the same chromatographic properties (on HPLC and TLC) as S; (5) kidney tissues released significantly more immunoassayable S into the incubation medium than gill, liver or gonad tissues. One interpretation of these results is that the corticosteroid production of the sea lamprey, one of the oldest extant vertebrates, is regulated through multiple pathways rather than the classical HPI-axis. However, the responsiveness of this steroid to the GnRH peptides means that a reproductive rather than a stress role for this steroid cannot yet be ruled out.

General and Comparative Endocrinology↗
USGS2013

Detections, concentrations, and distributional patterns of compounds of emerging concern in the San Antonio River Basin, Texas, 2011-12

During 2011&ndash;12, the U.S. Geological Survey, in cooperation with the San Antonio River Authority, evaluated detections, concentrations, and distributional patterns of selected compounds of emerging concern (hereinafter referred to as &ldquo;CECs&rdquo;) from water-quality samples (hereinafter referred to as &ldquo;samples&rdquo;) collected at a total of 20 sampling sites distributed throughout the San Antonio River Basin, Texas. Of the 54 wastewater compounds analyzed, 32 were detected in at least one sample collected from the San Antonio River Basin, and 22 of those compounds were not detected in any samples. The flame retardants tris (2-chloroethyl) phosphate and tris (dichloroisopropyl) phosphate, both possible endocrine disruptors, were the most frequently detected wastewater compounds with 28 of the 33 samples analyzed for wastewater compounds having measureable concentrations of those compounds. Of the 13 analyzed pharmaceuticals, 4 compounds were detected in a least one sample. Carbamazepine, an anticonvulsant, was the most frequently detected prescription pharmaceutical with 24 detections in 34 samples analyzed for pharmaceuticals. Of the 17 steroidal hormones, 4 were detected in at least one sample from the San Antonio River Basin. Estrone was detected in 9 of 34 samples analyzed for steroidal hormones, making it the most frequently detected steroidal hormone. Of the 4 sterols, all 4 were detected in at least one sample from the San Antonio River Basin. Cholesterol, detected in 19 of 34 samples analyzed for sterols, was the most frequently detected sterol. Three synoptic sampling events were completed as part of this study. The first and second synoptic sampling events included samples collected at the same 12 sampling sites. During the first and second synoptic sampling events, the lowest number of detections (2 and 0, respectively) and the lowest total concentrations of all measured compounds (0.62 and not measureable, respectively) occurred in samples collected at the Macdona site (Medina River near Macdona, Tex.). The highest number of detections (21 and 23, respectively) and highest total concentrations of all measured compounds (7.75 and 3.97 micrograms per liter [&micro;g/L], respectively) occurred in samples collected at the SAR Elmendorf site (San Antonio River near Elmendorf, Tex.). The third synoptic sampling event included samples collected at seven sites that were added to the study after the first two synoptic sampling events were completed. During the third synoptic sampling event, the lowest number of detections (two) and the lowest total concentration (0.14 &micro;g/L) of compounds were measured in samples collected at the North Prong site (North Prong Medina River above confluence Wallace Creek near Medina, Tex.). The highest number of detections (21) occurred at the SAR Mitchell site (San Antonio River at Mitchell Street, San Antonio, Tex.). The Dos Rios site (the Dos Rios wastewater treatment plant outfall at San Antonio, Tex.) had the highest total concentration of all measured compounds (4.37 &micro;g/L) in the third synoptic sampling event. Because Ecleto Creek flows only intermittently at the Ecleto site (Ecleto Creek near Runge, Tex.), samples from the Ecleto site were collected at different times than were samples from the other sites and were not included in a synoptic sampling event. The presence of wastewater compounds at the Ecleto site indicates that at least some wastewater compounds can be introduced into surface waters in rural parts of the San Antonio River Basin during runoff or because of onsite wastewater system seepage. The steroidal hormone and sterols detected at the Ecleto site, including estrone, cholesterol, beta -sitosterol, and beta -stigmastanol, likely were derived from cattle waste rather than from wastewater effluent. The distributional patterns of detections and concentrations of individual compounds and compound classes show the influence of wastewater-treatment plant (WWTP) outfalls on the quality of water in the San Antonio River Basin. In the Medina River Subbasin, the minimal influence of wastewater is evident as far downstream as the Macdona site. Downstream from the Macdona site, the Medina River receives treated municipal wastewater from both the Medio Creek Water Recycling Center site from an unnamed tributary at the plant and the Leon Creek Water Recycling Center site from Comanche Creek at the plant, and corresponding increases in both the number of detections and the total concentrations of all measured compounds at all downstream sampling sites were evident. Similarly, the San Antonio River receives treated municipal wastewater as far upstream as the SAR Witte site (San Antonio River at Witte Museum, San Antonio, Tex.) and additional WWTP outfalls along the Medina River upstream from the confluence of the Medina and San Antonio Rivers. Consequently, all samples collected along the main stem of the San Antonio River had higher concentrations of CECs in comparison to sites without upstream WWTPs. Sites in urbanized areas without upstream WWTPs include the Leon 35 site (Leon Creek at Interstate Highway 35, San Antonio, Tex.), the Alazan site (Alazan Creek at Tampico Street, San Antonio, Tex.), and the San Pedro site (San Pedro Creek at Probandt Street, at San Antonio, Tex.). The large number of detections at sites with no upstream wastewater source demonstrated that CECs can be detected in streams flowing through urbanized areas without a large upstream source of treated municipal wastewater. A general lack of detection of pharmaceuticals in streams without upstream outfalls of treated wastewater appears to be typical for streams throughout the San Antonio River Basin and may be a useful indicator of point-source versus nonpoint-source contributions of these compounds in urban streams. Observations of lower concentrations of compounds at the furthest downstream sampling sites in the basin indicate some natural attenuation of these compounds during transport; however, a more focused assessment is needed to make this determination.

Texas↗
USGS1996

Immune and endocrine responses of adult spring Chinook salmon during freshwater migration and sexual maturation

The immune –endocrine responses in spring chinook salmon ( Oncorhynchus tshawytscha ) were examined during their freshwater migration and final maturation. In 1990, migrating fish had high plasma cortisol titres (means 200 ng ml −1 ) and generated relatively few antibody-producing cells (APC) from peripheral blood leukocytes (PBL) (100 –200 per culture). After three weeks acclimation in constant environmental conditions, plasma cortisol was reduced and APC increased. There were no changes in number or affinity of glucocorticoid receptors. Concentrations of several sex steroids correlated with APC in females, but there were no such correlations in males. In 1993, fish in a hatchery had significantly greater cortisol concentrations in primary circulation than in secondary circulation, but sex steroid concentrations did not differ between circulations. Mean lysozyme activity in the primary and secondary circulation did not differ in June. In August, activity in the primary circulation was significantly less than that of the secondary, perhaps the result of acute stress associated with sampling. While some sex steroids correlated with lysozyme activity, the fact that in both years all endocrine and immune variables that correlated with each other also correlated with the date of sample, raises the question as to whether or not these are cause-and-effect relations.

Fish and Shellfish Immunology↗
USGS2014

Experimental West Nile virus infection in Eastern Screech Owls (Megascops asio)

This study evaluated the potential effects of different concentrations of bleached/unbleached kraft mill effluent (B/UKME) on several reproductive endpoints in adult largemouth bass ( Micropterus salmoides ). The kraft mill studied produces a 50/50 mix of bleached/unbleached market pulp with an estimated release of 36 million gal of effluent/day. Bleaching sequences were C 90 d 10 EopHDp and CEHD for softwood (pines) and hardwoods (mainly tupelo, gums, magnolia, and water oaks), respectively. Bass were exposed to different effluent concentrations (0 [controls, exposed to well water], 10, 20, 40, or 80%) for either 28 or 56 days. At the end of each exposure period, fish were euthanized, gonads collected for histological evaluation and determination of gonadosomatic index (GSI), and plasma was analyzed for 17β-estradiol, 11-ketotestosterone, and vitellogenin (VTG). Largemouth bass exposed to B/UKME responded with changes at the biochemical level (decline in sex steroids in both sexes and VTG in females) that were usually translated into tissue/organ-level responses (declines in GSI in both sexes and in ovarian development in females). Although most of these responses occurred after exposing fish to 40% B/UKME concentrations or greater, some were observed after exposures to 20% B/UKME. These threshold concentrations fall within the 60% average yearly concentration of effluent that exists in the stream near the point of discharge (Rice Creek), but are above the <10% effluent concentration present in the St. Johns River. The chemical(s) responsible for such changes as well as their mode(s) of action remain unknown at this time.

Florida↗
USGS1992

Hydrous pyrolysis of crude oil in gold-plated reactors

Crude oils from Iraq and California have been pyrolyzed under hydrous conditions at 200 and 300°C for time periods up to 210 days, in gold-plated reactors. Elemental (vanadium, nickel), stable isotopic (carbon), and molecular ( n -alkanes, acyclic isoprenoids, steranes, terpanes and aromatic steroid hydrocarbons) analyses were made on the original and pyrolyzed oils. Various conventional crude oil maturity parameters, including 20 S /(20 S + 20 R )-24-ethylcholestane ratios and the side-chain-length distribution of aliphatic and aromatic steroidal hydrocarbons, were measured in an effort to assess the modification of molecular maturity parameters in clay-free settings, similar to those encountered in “clean” reservoirs. Concentrations of vanadium and nickel in the Iraq oil decrease significantly and the V/(V + Ni) ratio decreases slightly, with increasing pyrolysis time/temperature. Whole oil carbon isotope ratios remain fairly constant during pyrolysis, as do hopane/sterane ratios and carbon number distribution of 5 α (H),14 α (H),17 α (H),20 R steranes. These latter three parameters are considered maturity-invariant. The ratios of short side-chain components to long side-chain components of the regular steranes [C 21 /(C 21 + C 29 R )] and the triaromatic steroid hydrocarbons [C 21 /(C 21 + C 28 )] vary systematically with increasing pyrolysis time, indicating that these parameters may be useful as molecular maturity parameters for crude oils in clay-free reservoir rocks. In addition, decreases in bisnorhopane/hopane ratio with increasing pyrolysis time, in a clay-free and kerogen-free environment, suggest that the distribution of these compounds is controlled by either differential thermal stabilities or preferential release from a higher-molecular weight portion of the oil.

Organic Geochemistry↗
USGS2015

Novel associations between contaminant body burdens and biomarkers of reproductive condition in male Common Carp along multiple gradients of contaminant exposure in Lake Mead National Recreation Area, USA

Adult male Common Carp were sampled in 2007/08 over a full reproductive cycle at Lake Mead National Recreation Area. Sites sampled included a stream dominated by treated wastewater effluent, a lake basin receiving the streamflow, an upstream lake basin (reference), and a site below Hoover Dam. Individual body burdens for 252 contaminants were measured, and biological variables assessed included physiological [plasma vitellogenin (VTG), estradiol-17&beta; (E2), 11-ketotestosterone (11KT)] and organ [gonadosomatic index (GSI)] endpoints. Patterns in contaminant composition and biological condition were determined by Principal Component Analysis, and their associations modeled by Principal Component Regression. Three spatially distinct but temporally stable gradients of contaminant distribution were recognized: a contaminant mixture typical of wastewaters (PBDEs, methyl triclosan, galaxolide), PCBs, and DDTs. Two spatiotemporally variable patterns of biological condition were recognized: a primary pattern consisting of reproductive condition variables (11KT, E2, GSI), and a secondary pattern including general condition traits (condition factor, hematocrit, fork length). VTG was low in all fish, indicating low estrogenic activity of water at all sites. Wastewater contaminants associated negatively with GSI, 11KT and E2; PCBs associated negatively with GSI and 11KT; and DDTs associated positively with GSI and 11KT. Regression of GSI on sex steroids revealed a novel, nonlinear association between these variables. Inclusion of sex steroids in the GSI regression on contaminants rendered wastewater contaminants nonsignificant in the model and reduced the influence of PCBs and DDTs. Thus, the influence of contaminants on GSI may have been partially driven by organismal modes-of-action that include changes in sex steroid production. The positive association of DDTs with 11KT and GSI suggests that lifetime, sub-lethal exposures to DDTs have effects on male carp opposite of those reported by studies where exposure concentrations were relatively high. Lastly, this study highlighted advantages of multivariate/multiple regression approaches for exploring associations between complex contaminant mixtures and gradients and reproductive condition in wild fishes.

General and Comparative Endocrinology↗
USGS1999

Masculinization of Nile tilapia ( Oreochromis niloticus ) by immersion in androgens

The use of all-male populations increases the efficiency and feasibility of tilapia aquaculture. The objective of this study was to determine the efficacy of a short-term immersion procedure for masculinizing Nile tilapia ( Oreochromis niloticus ). Two synthetic androgens were evaluated: 17α-methyldihydrotestosterone (MDHT) and 17α-methyltestosterone (MT). Exposure (3 h) on 10 and again on 13 days post-fertilization to MDHT at 500 μg/1 successfully masculinized fry in all experiments, resulting in 100, 94 and 83 ± 2% males in Experiments 1, 2 and 3, respectively. Immersions in MDHT or MT at 100 μg/1 resulted in significantly skewed sex ratios in Experiments 1 and 3 (MT resulted in 73 and 83 ± 3% males; and MDHT resulted in 72 and 91 ± 1% males) but not in Experiment 2. Immersion in MT at 500 μg/1 only caused masculinization in Experiment 3. Although further research and refinement is needed, immersion of Nile tilapia in MDHT may provide a practical alternative to the use of steroid-treated feed. Furthermore, when compared with current techniques for steroid-induced sex inversion of tilapia, short-term immersion reduces the period of time that workers are exposed to anabolic steroids.

Aquaculture↗