The psychoactive drug Escitalopram affects swimming behaviour and increases boldness in zebrafish (Danio rerio).

Selective serotonin re-uptake inhibitors are pharmaceuticals used to treat a range of psychological disorders. They are frequently found in surface waters in populated areas. In recent years, they have been shown to affect the behaviour of various aquatic organisms in a way that can have ecological effects. In this study, we exposed zebrafish of both sexes to nominally 0.00, 0.15 and 1.50 µg L-1 Escitalopram in flow-through tanks for three weeks. Subsequently, ten swimming behaviour parameters were quantified using high-resolution video tracking. There were noticeable gender differences in the behaviour responses to Escitalopram. Female fish exposed to 1.50 µg L-1 Escitalopram had a lower maximum swimming velocity, stopped less often and exhibited increased boldness (reduced thigmotaxis) compared to controls. Male fish exposed to 1.50 µg L-1 had a lower maximum swimming velocity compared to control fish. At the end of exposures, both length and weight of the females exposed to 1.50 µg L-1 Escitalopram were significantly less than the group of control fish. In addition, males exposed to 1.50 µg L-1 Escitalopram were significantly shorter than control fish. The behaviour, weight and body length of the fish exposed to nominally 0.15 µg L-1 was not significantly different from control fish in either sex. The results of this study demonstrate that Escitalopram can affect subtle but ecologically important aspects of fish behaviour and lends further credibility to the assumption that Escitalopram is an environmentally active pharmaceutical.

Concurrent effects of cold and hyperkalaemia cause insect chilling injury.

Chilling injury and death are the ultimate consequence of low temperature exposure for chill susceptible insects, and low temperature tolerance is considered one of the most important factors determining insect distribution patterns. The physiological mechanisms that cause chilling injury are unknown, but chronic cold exposure that causes injury is consistently associated with elevated extracellular [K(+)], and cold tolerant insects possess a greater capacity to maintain ion balance at low temperatures. Here, we use the muscle tissue of the migratory locust (Locusta migratoria) to examine whether chill injury occurs during cold exposure or following return to benign temperature and we specifically examine if elevated extracellular [K(+)], low temperature, or a combination thereof causes cell death. We find that in vivo chill injury occurs during the cold exposure (when extracellular [K(+)] is high) and that there is limited capacity for repair immediately following the cold stress. Further, we demonstrate that that high extracellular [K(+)] causes cell death in situ, but only when experienced at low temperatures. These findings strongly suggest that that the ability to maintain ion (particularly K(+)) balance is critical to insect low temperature survival, and highlight novel routes of study in the mechanisms regulating cell death in insects in the cold.

Urokinase-type plasminogen activator-like proteases in teleosts lack genuine receptor-binding epidermal growth factor-like domains.

Plasminogen activation catalyzed by urokinase-type plasminogen activator (uPA) plays an important role in normal and pathological tissue remodeling processes. Since its discovery in the mid-1980s, the cell membrane-anchored urokinase-type plasminogen activator receptor (uPAR) has been believed to be central to the functions of uPA, as uPA-catalyzed plasminogen activation activity appeared to be confined to cell surfaces through the binding of uPA to uPAR. However, a functional uPAR has so far only been identified in mammals. We have now cloned, recombinantly produced, and characterized two zebrafish proteases, zfuPA-a and zfuPA-b, which by several criteria are the fish orthologs of mammalian uPA. Thus, both proteases catalyze the activation of fish plasminogen efficiently and both proteases are inhibited rapidly by plasminogen activator inhibitor-1 (PAI-1). But zfuPA-a differs from mammalian uPA by lacking the exon encoding the uPAR-binding epidermal growth factor-like domain; zfuPA-b differs from mammalian uPA by lacking two cysteines of the epidermal growth factor-like domain and a uPAR-binding sequence comparable with that found in mammalian uPA. Accordingly, no zfuPA-b binding activity could be found in fish white blood cells or fish cell lines. We therefore propose that the current consensus of uPA-catalyzed plasminogen activation taking place on cell surfaces, derived from observations with mammals, is too narrow. Fish uPAs appear incapable of receptor binding in the manner known from mammals and uPA-catalyzed plasminogen activation in fish may occur mainly in solution. Studies with nonmammalian vertebrate species are needed to obtain a comprehensive understanding of the mechanism of plasminogen activation.

Superparamagnetic iron oxide polyacrylic acid coated γ-Fe2O3 nanoparticles do not affect kidney function but cause acute effect on the cardiovascular function in healthy mice.

This study describes the distribution of intravenously injected polyacrylic acid (PAA) coated γ-Fe(2)O(3) NPs (10 mg kg(-1)) at the organ, cellular and subcellular levels in healthy BALB/cJ mice and in parallel addresses the effects of NP injection on kidney function, blood pressure and vascular contractility. Magnetic resonance imaging (MRI) and transmission electron microscopy (TEM) showed accumulation of NPs in the liver within 1h after intravenous infusion, accommodated by intracellular uptake in endothelial and Kupffer cells with subsequent intracellular uptake in renal cells, particularly the cytoplasm of the proximal tubule, in podocytes and mesangial cells. The renofunctional effects of NPs were evaluated by arterial acid-base status and measurements of glomerular filtration rate (GFR) after instrumentation with chronically indwelling catheters. Arterial pH was 7.46±0.02 and 7.41±0.02 in mice 0.5 h after injections of saline or NP, and did not change over the next 12 h. In addition, the injections of NP did not affect arterial PCO(2) or [HCO(3)(-)] either. Twenty-four and 96 h after NP injections, the GFR averaged 0.35±0.04 and 0.35±0.01 ml min(-1) g(-1), respectively, values which were statistically comparable with controls (0.29±0.02 and 0.33±0.1 ml(-1) min(-1) 25 g(-1)). Mean arterial blood pressure (MAP) decreased 12-24 h after NP injections (111.1±11.5 vs 123.0±6.1 min(-1)) associated with a decreased contractility of small mesenteric arteries revealed by myography to characterize endothelial function. In conclusion, our study demonstrates that accumulation of superparamagnetic iron oxide nanoparticles does not affect kidney function in healthy mice but temporarily decreases blood pressure.

Reversibility of estrogenic sex changes in zebrafish (Danio rerio).

Development of male zebrafish (Danio rerio) courtship behavior was studied following estrogenic disruption of sexual differentiation. Sixty zebrafish were exposed at 28 degrees C to 5 ng/L (nominal concentration) of 17alpha-ethinylestradiol (EE2) from the egg stage until adulthood at four months of age, resulting in a female-biased sex ratio. Twenty-five EE2-exposed phenotypic female zebrafish were subsequently held in clean water for eight months. During this period, eight phenotypic males developed. These phenotypic males demonstrated significant behavioral aberrations and a low fertilization rate compared to control males.

The Psychoactive Drug Escitalopram Affects Foraging Behavior in Zebrafish (Danio rerio).

Selective serotonin reuptake inhibitors (SSRIs) are psychoactive pharmaceuticals that have been detected intact in natural waters globally. Laboratory experiments have reported that several SSRIs inhibit fish foraging behavior, but data for the SSRI escitalopram are lacking. The objectives of the present study were to determine whether escitalopram affects feeding behavior in zebrafish and whether possible sex differences exist. We exposed female and male zebrafish (Danio rerio) to 0.00, 0.10, and 1.50 µg/L of escitalopram in flow-through tanks for a 3-wk exposure period. We used a video tracking system with high temporal and spatial resolution to collect data on zebrafish swimming patterns in test tanks containing a food source. The results show a more pronounced effect of escitalopram in males compared with females. At the assumed most environmentally relevant concentration (0.10 µg/L), male average feeding time/visit and maximum feeding duration were significantly reduced by 27 and 42%, respectively. In addition, male total feeding duration was also significantly reduced (by 73%) at the highest concentration (1.50 µg/L). In females, only the maximum feeding duration was significantly reduced (by 41%) in the 0.10 µg/L treatment group. Hence, we reject our initial hypothesis that female feeding behavior is more vulnerable to escitalopram. There was no effect of escitalopram on length or weight among the experimental groups. The present study demonstrates that escitalopram, like other SSRIs, can inhibit fish foraging behavior and therefore potentially disturb natural food chains. Finally, our study suggests that SSRIs can both be sex and behavior specific. Environ Toxicol Chem 2019;38:1902-1910. © 2019 SETAC.

Male zebrafish (Danio rerio) courtship behaviour resists the feminising effects of 17alpha-ethinyloestradiol--morphological sexual characteristics do not.

The reproductive success of most fish depends partly on their ability to perform correct courtship behaviour. Alteration of this behaviour due to xenooestrogens can potentially affect the reproductive output and consequently population dynamics. In this lifetime study, zebrafish (Danio rerio) were exposed to environmentally realistic (0.05, 0.50 and 5.00 ng L(-1)) nominal concentrations of 17alpha-ethinyloestradiol (EE2) in a flow-through system for 4 months, from egg until sexual maturity. At 0.05 ng EE2L(-1), the secondary sexual characteristics of the males were significantly feminised with development of urogenital papillae and change in body colour. At 0.50 ng EE2L(-1), the sex ratio was altered from 69% males in the control groups to 59% males. The courtship behaviour of the male zebrafish was not affected by these two lower EE2 concentrations. Only at the highest concentration of 5.00 ng EE2L(-1), where only 5% of the group developed into males, was a change in behaviour recorded, and these few males were unable to induce spawning. Accordingly, the courtship behaviour of zebrafish is more resistant to oestrogenic exposure than secondary sexual characteristics and gonad development. This study provides the first quantitative measure of zebrafish courtship behaviour.

Quantitative studies on the effects of environmental estrogens on the testis of the guppy, Poecilia reticulata.

Estrogens that enter into the water system, such as by sewage effluent, may affect the reproductive capabilities of aquatic animals. The guppy (Poecilia reticulata) was chosen as a model organism to test the level of disturbances in primary and secondary sexual characteristics. Male guppies were exposed to 17beta-estradiol (10 and 50 ng L(-1)), and 17alpha-ethinylestradiol (10, 50 and 200 ng L(-1)) for 3.5 months from birth to adulthood. Specimens were euthanized and the testes removed for histological examination, applied in conjunction with stereological technique. Alterations in the quantity of sperm, decreasing intensity of body coloration, and increased body weight were generally significant only in the group exposed to 200 ng L(-1) of 17alpha-ethinylestradiol. No significant changes were seen in the gonadosomal index (GSI). Quantification of the developmental stages of spermatogenesis indicated a trend of greater representation of later stages in specimens exposed to low doses of estrogens, and greater prevalence of early stages in those exposed to high doses of estrogens. Based on the results of this study, environmental estrogens do not seem to pose a reproductive threat to guppies. It is concluded that stereological histology can be considered a valuable tool in quantifying estrogenic effects upon fish gonads and that the guppy is perhaps not an ideal test organism for estrogenic exposure due to limited sensitivity.

Differences in Reproductive Behavior between Spawning and Non-Spawning Zebrafish Pairs and the Effects of 17α-Ethinylestradiol (EE2).

Reproductive success manifested by spawning and fertilization, in most fish, depends partly on an appropriate courtship behavior by both sexes. The zebrafish reproductive behavior can be resolved in some of its constituent elements by a computerized vision system and described in unbiased quantitative terms. Pairs of adult male and female zebrafish were monitored with automatic video tracking at 16 Hz for 45 min in a tank with a spawning area in one corner. Subsequently, spawning, if any, was registered and the swimming behavior and mutual interactions of the two fish were quantified. Further, temporal and frequency distributions of average velocity and turning rate were produced. It is demonstrated that the courtship behavior in spawning pairs differs markedly from non-spawning pairs with differences in both male and female behavior. EE2 (17α-ethinylestradiol), a contraceptive hormone found in aquatic environments, has only a slight effect on these behavior differences between spawning and non-spawning pairs.

Disrupted reproductive behavior in unexposed female zebrafish (Danio rerio) paired with males exposed to low concentrations of 17α-ethinylestradiol (EE2).

Estrogenic substances, including the contraceptive pharmaceutical 17α-ethinylestradiol (EE2), pose a threat to aquatic wildlife causing endocrine disturbances of physiological processes and reproductive behavior. We have previously demonstrated that the reproductive behavior of male zebrafish, Danio rerio, remain intact after lifelong exposure to low concentrations of EE2 (0.05 and 0.5ngL(-1)), concentrations high enough to cause morphological alterations of the male phenotype. Despite normal courtship behavior, the reproductive output is suppressed when these males were paired with unexposed females. In this study, we include the female courtship behavior in the analyzes of EE2's effects on behavior. Groups of male zebrafish were exposed to nominally 0, 1, 3 and 10ngL(-1) of EE2 from hatching to adulthood and subsequently individually paired with an unexposed female. Eleven distinct elements of the reproductive behavior were then extracted and analyzed using an automated video tracking system. Subsequently, male brains were isolated and the expression of genes encoding estrogenic receptors ERα, ERß1 and ERß2, the androgen receptor AR, and the aromatase cyp19a1b were compared with the expression in brains of unexposed males. (In this article gene expression is taken synonymous to transcription, although it is acknowledged that it can also be regulated by, e.g., mRNA and protein stability, and translation). The results confirmed that the male reproductive behavior was unaffected by the EE2 treatments. Also, the expressions of genes encoding estrogen and androgen receptors were unaffected. Only the gene encoding aromatase was 0.6 fold down-regulated. In contrast, and most surprisingly, nearly all the elements in the female courtship behavior were significantly disturbed, despite the fact that these females had never been exposed to EE2; most likely elicited by differences in male morphology, pheromones or some other unrevealed mechanism.

Disturbed sexual characteristics in male mosquitofish (Gambusia holbrooki) from a lake contaminated with endocrine disruptors.

Previous laboratory studies have demonstrated that estrogenic and antiandrogenic chemicals can alter several sexual characteristics in male poeciliid fishes. Whether similar disturbances occur under field conditions remains to be confirmed. Lake Apopka, Florida, is contaminated with numerous chemicals, some of which possess endocrine-disrupting activity. Male mosquitofish (Gambusia holbrooki) were collected monthly from December 2000 through May 2001 from Lake Apopka and two nearby reference lakes, Orange Lake and Lake Woodruff National Wildlife Refuge. Selected sexual characteristics were compared temporally and among lakes during the collection period. Male fish from Lake Apopka had slightly shorter gonopodia and on average 32 and 47% fewer sperm cells per milligram testis, when compared with the fish collected from Orange Lake and Lake Woodruff, respectively. The testes weights increased markedly during spring, with significantly smaller testes in fish from Lake Apopka than from Orange Lake, but surprisingly, the smallest testes occurred in males obtained from the Lake Woodruff population. The highest liver weights were found in the Lake Apopka population. Whole-body concentrations of testosterone and estradiol varied among months; the peak testosterone concentration occurred in January and was significantly lower in male fish from Lake Apopka compared with Orange Lake. The intensity of male courtship behavior was highly correlated to body testosterone concentration, but no statistically significant differences in sexual behavior among the lakes were found. We conclude that sexual characteristics of relevance to male reproductive capacity are altered in the Lake Apopka mosquitofish population, and we discuss the presence of chemicals with antiandrogenic effects in Lake Apopka as a possible cause of the observed alterations.

Exposure of juvenile guppies to three antiandrogens causes demasculinization and a reduced sperm count in adult males.

It has been thoroughly established that the fungicide vinclozolin and the persistent DDT metabolite p,p'-DDE, can function as antiandrogens in mammals in a manner similar to the therapeutic antiandrogen flutamide. In mammals, these chemicals bind the androgen receptor and prevent the transcription of the associated genes causing abnormal sexual development and demasculinization. There are few similar studies in fish and so far it has not been demonstrated that these chemicals have any antiandrogenic effects in this group. In the present study, juvenile guppies (Poecilia reticulata) were fed sublethal doses of vinclozolin, p,p'-DDE or flutamide from birth to adulthood. At sexual maturity, we measured a suite of male sexual characteristics that are known to be under androgen control. All three chemicals caused a reduction in the orange display coloration, inhibited gonopodium development, reduced the sperm count and suppressed courtship behaviour, in a manner consistent with antiandrogen action. Only the gonodosomatic index was unaffected by the treatments. In addition, the three chemicals skewed the sex ratio at adulthood and caused delayed maturation. The altered characters are all considered to be important for male mating success and their impairment indicates that antiandrogens may seriously compromise male reproductive fitness.

Altered social behavior and sexual characteristics in mosquitofish (Gambusia holbrooki) living downstream of a paper mill.

Several environmental contaminants have been found in paper mill effluent including substances with androgenic properties. The presence of androgenic substances in paper mill effluent was also indicated in the present study which demonstrated masculinized anal fins of female mosquitofish from the paper mill effluent contaminated Fenholloway River. In addition, when compared to the nearby Econfina River, which does not receive paper mill effluent, fewer females from the contaminated river were pregnant, they were smaller and their estradiol concentration exhibited greater variation. Males from the Fenholloway River and the Econfina River had similar sperm counts, but the testes were larger and greater variation in testosterone concentration was observed in male fish from the Fenholloway River. In males and females from the Fenholloway River, liver weights were increased and computer-aided behavior analysis demonstrated a reduction in their social behavior when compared to reference fish. We conclude that a number of sexual characteristics were affected in mosquitofish living in the paper mill contaminated Fenholloway River, with possible adverse effects on the reproduction of this population.

Towards a comprehensive catalog of zebrafish behavior 1.0 and beyond.

Zebrafish (Danio rerio) are rapidly gaining popularity in translational neuroscience and behavioral research. Physiological similarity to mammals, ease of genetic manipulations, sensitivity to pharmacological and genetic factors, robust behavior, low cost, and potential for high-throughput screening contribute to the growing utility of zebrafish models in this field. Understanding zebrafish behavioral phenotypes provides important insights into neural pathways, physiological biomarkers, and genetic underpinnings of normal and pathological brain function. Novel zebrafish paradigms continue to appear with an encouraging pace, thus necessitating a consistent terminology and improved understanding of the behavioral repertoire. What can zebrafish 'do', and how does their altered brain function translate into behavioral actions? To help address these questions, we have developed a detailed catalog of zebrafish behaviors (Zebrafish Behavior Catalog, ZBC) that covers both larval and adult models. Representing a beginning of creating a more comprehensive ethogram of zebrafish behavior, this effort will improve interpretation of published findings, foster cross-species behavioral modeling, and encourage new groups to apply zebrafish neurobehavioral paradigms in their research. In addition, this glossary creates a framework for developing a zebrafish neurobehavioral ontology, ultimately to become part of a unified animal neurobehavioral ontology, which collectively will contribute to better integration of biological data within and across species.

The normal acid-base status of mice.

Rodent models are commonly used for various physiological studies including acid-base regulation. Despite the widespread use of especially genetic modified mice, little attention have been made to characterise the normal acid-base status in these animals in order to reveal proper control values. Furthermore, several studies report blood gas values obtained in anaesthetised animals. We, therefore, decided to characterise blood CO(2) binding characteristic of mouse blood in vitro and to characterise normal acid-base status in conscious BALBc mice. In vitro CO(2) dissociation curves, performed on whole blood equilibrated to various PCO2 levels in rotating tonometers, revealed a typical mammalian pK' (pK'=7.816-0.234 × pH (r=0.34)) and a non-bicarbonate buffer capacity (16.1 ± 2.6 slyke). To measure arterial acid-base status, small blood samples were taken from undisturbed mice with indwelling catheters in the carotid artery. In these animals, pH was 7.391 ± 0.026, plasma [HCO(3)(-)] 18.4 ± 0.83 mM, PCO2 30.3 ± 2.1 mm Hg and lactate concentration 4.6 ± 0.7 mM. Our study, therefore, shows that mice have an arterial pH that resembles other mammals, although arterial PCO2 tends to be lower than in larger mammals. However, pH from arterial blood sampled from mice anaesthetised with isoflurane was significantly lower (pH 7.239 ± 0.021), while plasma [HCO(3)(-)] was 18.5 ± 1.4 mM, PCO2 41.9 ± 2.9 mm Hg and lactate concentration 4.48 ± 0.67 mM. Furthermore, we measured metabolism and ventilation (V(E)) in order to determine the ventilation requirements (VE/VO2) to answer whether small mammals tend to hyperventilate. We recommend, therefore, that studies on acid-base regulation in mice should be based on samples taken for indwelling catheters rather than cardiac puncture of terminally anaesthetised mice.

In Vivo Toxicity of Silver Nanoparticles and Silver Ions in Zebrafish (Danio rerio).

The influence of water chemistry on characterised polyvinyl pyrrolidone- (PVP-) coated silver nanoparticles (81 nm) was investigated. NaCl solution series of 100-800 mg L(-1) lead to initial and temporal increase in nanoparticles size, but agglomeration was limited. pH variation (5-8) had only minor influence on the hydrodynamic particle size. Acute toxicity of nanosivler to zebrafish (Danio rerio) was investigated in a 48-hour static renewal study and compared with the toxicity of silver ions (AgNO(3)). The nanosilver and silver ion 48-hour median lethal concentration (LC(50)) values were 84 µg L(-1) and 25 µg L(-1), respectively. To investigate exposure-related stress, the fish behaviour was observed visually after 0, 3, 6, 12, 24, 27, 30, and 48 hours of both nanosilver and ionic silver treatments. These observations revealed increased rate of operculum movement and surface respiration after nanosilver exposure, suggesting respiratory toxicity. The present study demonstrates that silver nanoparticles are lethal to zebrafish.

Silver nanoparticles disrupt olfaction in Crucian carp (Carassius carassius) and Eurasian perch (Perca fluviatilis).

The present study investigates the effect of silver nanoparticles on olfaction in Crucian carp (Carassius carassius) and Eurasian perch (Perca fluviatilis). The electro-olfactogram (EOG) signal was recorded by stimulating the olfactory epithelium with pulses of the odorant L-alanine during the pre-exposure, silver exposure and recovery periods, respectively. The nanosilver suspension concentrations applied were 0.00, 0.45 and 45 µg L⁻¹, respectively. Secondly, to compare the toxicity of silver nanoparticles with silver ions, perch were exposed to ionic silver. During exposure to nanosilver suspension, the olfactory epithelium rapidly hyperpolarized, which was not found after exposure to silver ion solution. Exposure to 0.45 µg L⁻¹ nanosilver suspension led to enhanced EOG responses, whereas exposure to 45 µg L⁻¹ silver nanoparticle suspension and silver ion solution resulted in suppressed EOG signals. The EOG signals partly recovered in silver-free water. The silver nanoparticle olfactory toxicity is believed to be a combination of silver particles and released silver ions.

Functional behavior and reproduction in androgenic sex reversed zebrafish (Danio rerio).

Endocrine-disrupting chemicals released into natural watercourses may cause biased sex ratios by sex reversal in fish populations. The present study investigated the androgenic sex reversal of zebrafish (Danio rerio) exposed to the androgenic compound 17beta-trenbolone (TB) and whether sex-changed females would revert to the female phenotype after cessation of TB exposure. 17beta-Trenbolone is a metabolite of trenbolone acetate, an anabolic steroid used as a growth promoter in beef cattle. 17beta-Trenbolone in runoff from cattle feedlots may reach concentrations that affect fish sexual development. Zebrafish were exposed to a concentration of 20 ng/L TB in a flow-through system for five months from egg until sexual maturity. This resulted in an all-male population. It was further found that all these phenotypic males displayed normal male courtship behavior and were able to reproduce successfully, implying that the sex reversal was complete and functional. None of the phenotypic males developed into females after six months in clean water, demonstrating that androgenic sex reversal of zebrafish is irreversible.

Silver nanoparticles and silver nitrate cause respiratory stress in Eurasian perch (Perca fluviatilis).

Silver nanoparticles are utilised in an increasing amount of products, and discharge to the aquatic environment is inevitable. Fish gills are in direct contact with the ambient water, making them potential exposed and vulnerable to suspended silver nanoparticles. The present study investigates the effect of silver nanoparticles (average 81 nm) on the oxygen consumption (M(O2)) in Eurasian perch (Perca fluviatilis), expressed by the basal metabolic rate (BMR) and the critical oxygen tension (P(crit)) below which the fish can no longer maintain aerobic metabolism. For comparison, the impact of silver nitrate (AgNO(3)), was examined as well. Perch were exposed to nominal concentrations of 63, 129 and 300 microg L(-1) silver nanoparticles and 39 and 386 microg L(-1) AgNO(3), respectively, plus controls which were not exposed to silver. M(O2) measured by automated intermittent closed respirometry. After one day acclimatization in the respirometer, the pre-exposure BMR was determined together with P(crit). Hereafter, nanoparticles or silver nitrate were added to the test tank and BMR and P(crit) were measured again the following day. The results demonstrate that nanosilver had no impact on the BMR, whereas exposure to 386 microg L(-1) AgNO(3) resulted in a significant raise in BMR. P(crit) was increased approximately 50% after exposure to 300 microg L(-1) nanosilver plus 31% and 48% by 39 microg L(-1)and 386 microg L(-1) silver nitrate, respectively. These findings reveal that exposure to nanosilver results in impairment of the tolerance to hypoxia. Possibly, nanosilver affects the gills externally, reducing the diffusion conductance which then leads to internal hypoxia during low water oxygen tensions (P(O2)).

p,p'-DDE fails to reduce the competitive reproductive fitness in Nigerian male guppies.

The ecologically highly important effect of intermale competition is assessed here in a new approach to evaluating endocrine disruption at the population level. A guppy (Poecilia reticulata) male exposed to the antiandrogenic DDT metabolite p,p'-DDE competed against an unexposed male for the opportunity to fertilize a female. Offspring were then assigned to sires using microsatellites in genetic paternity analysis. In addition, a suite of male sexual characteristics including sperm count, coloration, and sexual behavior were also measured. p,p'-DDE produced no significant harmful effect on either the male sexual characteristics or the success in siring young, although the highest sublethal dose tested was only a factor 10 below the dose producing 100% mortality. At present, data on the antiandrogenic potency of p,p'-DDE are highly ambiguous. This study supports the increasing amount of evidence that the demasculinizing action of this chemical is often weak and highly variable across populations, even within the same species.