Effects of bis(tributyltin)oxide on antipredator behavior in threespine stickleback Gasterosteus aculeatus L

Embryonic exposure to environmentally relevant levels of tributyltin affects embryonic tributyltin bioaccumulation and the physiological responses of juveniles in cuttlefish (Sepia pharaonis)

Tributyltin (TBT) is a typical organic pollutant that persists in aquatic sediments due to its wide usage as an antifouling fungicide during the past few decades. Despite increased awareness of the serious negative consequences of TBT on aquatic species, studies on the effects of TBT exposure on cephalopod embryonic development and juvenile physiological performance are scarce. To investigate the lasting effects of TBT toxicity on Sepia pharaonis from embryo to hatchling, embryos (gastrula stage, 3-5 h post fertilization) were exposed to four levels of TBT until hatching: 0 (control), 30 (environmental level), 60, and 120 ng/L. Subsequently, juvenile growth performance endpoints and behavioral alterations were assessed over 15 days post-hatching. Egg hatchability was significantly reduced and embryonic development (i.e., premature hatching) was accelerated in response to 30 ng/L TBT exposure. Meanwhile, TBT-induced alterations in embryonic morphology primarily included yolk-sac lysis, embryonic malformations, and uneven pigment distributions. During the pre-middle stage of embryonic development, the eggshell serves as an effective barrier to safeguard the embryo from exposure to 30-60 ng/L TBT, according to patterns of TBT accumulation and distribution in the egg compartment. However, even environmental relevant levels of TBT (30 ng/L) exposure during embryonic development had a negative impact on juvenile behavior and growth, including slowing growth, shortening eating times, causing more irregular movements, and increasing inking times. These findings indicate that after TBT exposure, negative long-lasting effects on S. pharaonis development from embryo to hatchling persist, suggesting that long-lasting toxic effects endure from S. pharaonis embryos to hatchlings.

Acclimation effect on fish behavioural characteristics: determination of appropriate acclimation period for different species

In the present study, the authors investigated the effect of acclimation duration (up to 4 h) on behavioural characteristics of taxonomically and functionally different fish species, i.e., the migratory rheophilic salmonids rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar), and the non-migratory eurytopic European perch (Perca fluviatilis) and three-spined stickleback (Gasterosteus aculeatus). Specifically, the authors explored fish behavioural patterns based on specific endpoints (average, maximum and angular velocity) during the acclimation period, and determined the acclimation period suitable for the tested fish species. The performed behavioural data analysis showed that the minimum time needed to adjust fish activity to a more stable (baseline) level should be at least 2 h for O. mykiss and S. salar and 1 h for G. aculeatus. Nonetheless, P. fluviatilis behaviour did not show significant changes during the 4 h acclimation. The results of this study revealed that the effect of the acclimation duration on such rheophilic species as O. mykiss and S. salar was greater than that on the eurytopic species P. fluviatilis and G. aculeatus, indicating that acclimation period is important in managing fish stress before behavioural observations. For all species, the highest variability was found in the endpoint of maximum velocity, and the lowest in that of angular velocity. This study showed that before starting actual toxicity testing experiments, it is important to determine an appropriate, species-specific acclimation period.

Mechanisms involved in tributyltin-enhanced aggressive behaviors and fear responses in male zebrafish

Tributyltin (TBT), an aromatase inhibitor, has been found to disrupt gametogenesis and reproductive behavior in several fish species. However, whether TBT is capable of affecting other behaviors such as aggressive behavior and fear response in fish and the underlying mode(s) of action remain unclear. To study aggressive behavior, adult zebrafish (Danio rerio) males were continuously exposed to two nominal concentrations of TBT (TBT-low, 100 ng/L and TBT-high, 500 ng/L) for 28 days. To study the fear response, the fish were divided into four groups (Blank and Control, 0 ng/L TBT; TBT-low, 100 ng/L; and TBT-high, 500 ng/L). The fish were then treated with DW (Blank) or with alarm substance (AS) (Control, TBT-low and TBT-high). After exposure, the aggressive behavior of the fish was tested using the mirror test (mirror-biting frequency, approaches to the mirror and duration in approach zone).and fighting test (fish-biting frequency) The mirror-biting frequency, approaches to the mirror, duration in approach zone and fish-biting frequency of the TBT-exposed fish increased significantly compared to those of the control fish, indicating enhanced aggressive behavior. The fear response parameters tested using the novel tank dive test (onset time to the higher half, total duration in the lower half and the frequency of turning) of the TBT-exposed fish were also significantly increased after AS administration, suggesting an enhanced fear response. Further investigation revealed that TBT treatment elevated the plasma level of 11-ketotestosterone (11-KT) and decreased the plasma level of estradiol (E2) in a concentration-dependent manner. Moreover, TBT up-regulated the mRNA levels of ar, c-fos and bdnf1, and suppressed the expression of btg-2 in fish. In addition, exposure to AS increased the plasma level of cortisol and down-regulated the mRNA expression levels of genes involved in 5-HT synthesis (such as tph1b and pet1) in both control and TBT-treated fish. AS significantly suppressed the mRNA level of tph1b, tph2, pet1 and npy in the TBT-high group compared to the control fish. The present study demonstrates that TBT enhances aggressive behavior and fear responses in male zebrafish probably through altering plasma levels of 11-KT, E2 and cortisol and altering the expression of genes involved in the regulation of aggressive behavior (ar, c-fos, bdnf1 and btg-2) and fear responses (tph1b, tph2, pet1 and npy). The present study greatly extends our understanding of the behavioral toxicity of TBT to fish.

Neurotoxicity of organophosphate pesticides could reduce the ability of fish to escape predation under low doses of exposure

Biomarkers are frequently used in ecotoxicology as they allow to study toxicant effects happening at low concentrations of exposure. However, most sublethal studies only evaluate cellular biomarkers which lack evident ecological relevance. We used a multibiomarker approach to estimate the toxic effects of ethoprophos, an organophosphate insecticide commonly used in banana plantations, on the tropical fish Astyanax aeneus (Characidae). We measured biomarkers at sub-individual (cellular) and individual (metabolism, behavior) levels and examined relationships among these responses. A sublethal exposure to ethoprophos caused a significant (54%) reduction of brain Cholinesterase (ChE) activity, reflecting the pesticide's high neurotoxicity. However, other biomarkers like oxidative stress, biotransformation reactions, and resting metabolic rate were not affected. Exposure to ethoprophos modified antipredator behaviors such as escape response and detection avoidance (light/dark preference): exposed fish escaped slower from a simulated attack and preferred brighter areas in a novel tank. The relationship between ChE activity and reaction time suggests that pesticide-induced ChE inhibition reduces escape ability in fish. Our results provide evidence that impacts of organophosphate pesticides on fish ecological fitness can occur even with short exposures at very low concentrations.

The role of intraspecies variation in fish neurobehavioral and neuropharmacological phenotypes in aquatic models

Intraspecies variation is common in both clinical and animal research of various brain disorders. Relatively well-studied in mammals, intraspecies variation in aquatic fish models and its role in their behavioral and pharmacological responses remain poorly understood. Like humans and mammals, fishes show high variance of behavioral and drug-evoked responses, modulated both genetically and environmentally. The zebrafish (Danio rerio) has emerged as a particularly useful model organism tool to access neurobehavioral and drug-evoked responses. Here, we discuss recent findings and the role of the intraspecies variance in neurobehavioral, pharmacological and toxicological studies utilizing zebrafish and other fish models. We also critically evaluate common sources of intraspecies variation and outline potential strategies to improve data reproducibility and translatability.

Tributyltin induces premature hatching and reduces locomotor activity in zebrafish (Danio rerio) embryos/larvae at environmentally relevant levels

Tributyltin (TBT) is an organotin compound that is the active ingredient of many biocides and antifouling agents. In addition to its well established role as an endocrine disruptor, TBT is also associated with adverse effects on the nervous system and behavior. In this study, zebrafish (Danio rerio) embryos were exposed to environmentally relevant concentrations of TBT (0.01, 0.1, 1 nM) to determine how low levels affected development and behavior. Fish exposed to 1 nM TBT hatched earlier when compared to controls. Following a 96-h exposure, total swimming distance, velocity, and activity of zebrafish larvae were reduced compared to controls. To identify putative mechanisms for these altered endpoints, we assessed embryo bioenergetics and gene expression. We reasoned that the accelerated hatch time could be related to ATP production and energy, thus embryos were exposed to TBT for 24 and 48-h exposure prior to hatch. There were no differences among groups for endpoints related to bioenergetics (i.e. basal, ATP-dependent, and maximal respiration). To address mechanisms related to changes in behavioral activity, we measured transcripts associated with muscle function (myf6, myoD, and myoG) and dopamine signaling (th, dat, dopamine receptors) as dopamine regulates behavior. No transcript was altered in expression by TBT in larvae, suggesting that other mechanisms exist that may explain changes in higher level endpoints. These results suggest that endpoints related to the whole animal (i.e. timing of hatch and locomotor behavior) are more sensitive to environmentally-relevant concentrations of TBT compared to the molecular and metabolic endpoints examined here.

Tributyltin affects shoaling and anxiety behavior in female rare minnow (Gobiocypris rarus)

Effects of tributyltin (TBT) on reproduction are well established in many fish species. However, few studies report the effects of TBT on non-reproductive behaviors, which is a novel aspect of endocrine disruption in fish. Thus, the present study used rare minnow (Gobiocypris rarus) to investigate the effects of TBT, at environmental concentrations of 1, 10 and 100ng/L, on shoaling and anxiety behaviors. The results showed that fish exposed to TBT had less group cohesion during the course of the 10-min observation period as compared with the control fish. Further, TBT altered the shoaling in the Novel tank test, where shoaling is determined as the tendency to leave a shoal of littermates trapped behind a Plexiglas barrier at one end of the test tank. Fish exposed to TBT had shorter latency before leaving shoal mates and spent more time away from shoal than control fish. In addition, we also used Novel tanks to study the anxiety behavior as the tendency to stay at the bottom when introduced into an unfamiliar environment. The fish exposed to TBT showed increased anxiety, manifested as increased latency to enter the upper half and decreased time in upper half when compared with the control fish. TBT exposure increased the levels of dopamine and its metabolite 3,4-dihydroxyphenylacetic acid, and decreased the levels of 5-hydroxytryptamine and its metabolite 5-hydroxy indole acetic acid in the brain. Thus, the hypofunction of the dopaminergic system or of the serotoninergic system or the combination of the two may underlie the observed behavioral change, which might affect the fitness of fish in their natural environment.

Disruptions in aromatase expression in the brain, reproductive behavior, and secondary sexual characteristics in male guppies (Poecilia reticulata) induced by tributyltin

Although bioaccumulation of tributyltin (TBT) in fish has been confirmed, information on possible effects of TBT on reproductive system of fish is still relatively scarce, particularly at environmentally relevant levels. To evaluate the adverse effects and intrinsic toxicological properties of TBT in male fish, we studied aromatase gene expression in the brain, sex steroid contents, primary and secondary sexual characteristics, and reproductive behavior in male guppies (Poecilia reticulata) exposed to tributyltin chloride at the nominal concentrations of 5, 50, and 500 ng/L for 28 days in a semi-static exposure system. Radioimmunoassay demonstrated that treatment with 50 ng/L TBT caused an increase in systemic levels of testosterone of male guppies. Gonopodial index, which showed a positive correlation with testosterone levels, was elevated in the 5 ng/L and 50 ng/L TBT treated groups. Real-time PCR revealed that TBT exposure had inhibiting effects on expression of two isoforms of guppy aromatase in the brain, and these changes at the molecular levels were associated with a disturbance of reproductive behavior of the individuals, as measured by decreases in frequencies of posturing, sigmoid display, and chase activities when males were paired with females. This study provides the first evidence that TBT can cause abnormalities of secondary sexual characteristics in teleosts and that suppression of reproductive behavior in teleosts by TBT is due to its endocrine-disrupting action as an aromatase inhibitor targeting the nervous system.

Ecotoxicological effects of waterborne PFOS exposure on swimming performance and energy expenditure in juvenile goldfish (Carassius auratus)

The potential risks of perfluorooctane sulfonate (PFOS) are of increasing ecological concern. Swimming performance is linked to the fitness and health of fish. However, the impacts of PFOS on swimming performance remain largely unknown. We investigated the ecotoxicological effects of acute exposure to PFOS on the swimming performance and energy expenditure of juvenile goldfish (Carassius auratus). The fish were exposed to a range of PFOS concentrations (0, 0.5, 2, 8 and 32 mg/L) for 48 hr. The spontaneous swimming activity, fast-start swimming performance, critical swimming speed (U(crit)) and active metabolic rate (AMR) of the goldfish were examined after exposure to PFOS. PFOS exposure resulted in remarkable effects on spontaneous activity. Motion distance was reduced, and the proportion of motionless time increased with increasing concentrations of PFOS. However, no significant alterations in the fast-start performance-related kinematic parameters, such as latency time, maximum linear velocity, maximum linear acceleration or escape distance during the first 120 msec after stimulus, were observed after PFOS exposure. Unexpectedly, although PFOS exposure had marked influences on the swimming oxygen consumption rates and AMR of goldfish, the U(crit) of the goldfish was not significantly affected by PFOS. This may result in a noteworthy increase in the energetic cost of transport. The overall results indicate that, in contrast to spontaneous activity, underlying swimming capabilities are maintained in goldfish after short-term exposure to PFOS, but energy expenditure during the process of swimming is dramatically aggravated.

iPhone® applications as versatile video tracking tools to analyze behavior in zebrafish (Danio rerio)

Zebrafish (Danio rerio) are emerging as a promising model organism for experimental studies relevant to biological psychiatry. The objective of this study was to develop a novel video-based movement tracking and analysis system to quantify behavioral changes following psychoactive drug exposure in zebrafish. We assessed the effects of withdrawal from chronic ethanol exposure, and subsequent administration of fluoxetine (Prozac®), buspirone (Buspar®), and diazepam (Valium) using two behavioral paradigms; the Novel Tank Diving Test and the Light/Dark Choice Assay. A video tracking system was developed using two Apple® applications (Apps) to quantify these behaviors. Data from zebrafish exposed to the above treatments are presented in this paper not only to exemplify behavioral alterations associated with chronic exposure, but also more importantly, to validate the video tracking system. Following withdrawal from chronic ethanol exposure, zebrafish exhibited dose/time-dependent anxiogenic effects; including reduced exploration and freezing behavior in the Novel Tank Diving Test, and preference for the dark area for the Light/Dark Choice Assay. In contrast, the above drug treatments had significant anxiolytic effects. We have developed a simple and cost-effective method of measuring zebrafish behavioral responses. The iPhone® Apps outlined in this study offer numerous flexible methods of data acquisition; namely, ease of identification and tracking of multiple animals, tools for visualization of the tracks, and calculation of a range of analysis parameters. Furthermore, the limited amount of time required for interpretation of the video data makes this a powerful high-throughput tool with potential applications for pre-clinical drug development.

Tributyltin exposure influences predatory behavior, neurotransmitter content and receptor expression in Sebastiscus marmoratus

Tributyltin (TBT) is a ubiquitous marine contaminant due to its extensive use as a biocide, fungicide and antifouling agent. However, the neurotoxic effect of TBT has not been extensively studied, especially in marine fish. This study was conducted to investigate the effects of TBT (10, 100 and 1000 ng/L) on the predatory behavior of Sebastiscus marmoratus and to look into the mechanism involved. The results showed that TBT exposure depressed predatory activity after 50 days exposure. Dopamine levels in the fish brains increased in a dose-dependent manner, while 5-hydroxytryptamine and norepinephrine levels decreased significantly in the TBT exposure group compared to the control. The mRNA levels of dopamine receptors, which have functions such as cognition, motor activity, motivation and reward, mood, attention and learning, were significantly down-regulated by TBT exposure. Although the levels of amino acid neurotransmitters, including glutamate, did not show marked alteration, the expression of the glutamatergic signaling pathway such as N-methyl-D-aspartate receptors, a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor, calmodulin, Ca(2+)/calmodulin-dependent protein kinases-II and cyclic adenosine monophosphate responsive element binding protein, was significantly reduced by TBT exposure, which indicated that central nerve activities were in a state of depression, thus affecting the predatory activities of the fish.

A video-based movement analysis system to quantify behavioral stress responses of fish

Behavioral alterations can be measured as endpoints for sublethal toxicity, and serve as a tool for environmental risk assessment and analysis of toxicological impact. Numerous technical and biological factors have made sublethal effects on fish behavior difficult to quantify. In order to investigate stress- and contaminant-induced behavioral alterations, a video analysis system was designed by our laboratory. With this system up to 12 fish may be individually housed in 20 L exposure arenas and automatically videotaped at multiple and discrete intervals during an experimental period. Analog video data can then digitized, converted into x,y coordinates, and finally transformed into relevant behavioral endpoints using software designed for tracking fish movement combined with specific algorithms. These endpoints include velocity, total distance traveled, angular change, percent movement, space utilization, and fractal dimension (path complexity). Data from fish exposed to a reference toxicant, MS222, and simulation experiments, are presented to exemplify alterations in fish behavior associated with exposure, and accuracy and precision, respectively. The system provides flexibility to analyze any observed movement behavior, is remotely controlled, and can be transportable. These movement analyses can be used to identify characteristic behavioral responses to a variety of environmentally-relevant stressors, and assist in risk assessment and the development of more sensitive lowest observable effect level and no observable effect level for sentinel species.

The effects of environmental pollutants on complex fish behaviour: integrating behavioural and physiological indicators of toxicity

Environmental pollutants such as metals, pesticides, and other organics pose serious risks to many aquatic organisms. Accordingly, a great deal of previous research has characterized physiological mechanisms of toxicity in animals exposed to contaminants. In contrast, effects of contaminants on fish behaviour are less frequently studied. Because behaviour links physiological function with ecological processes, behavioural indicators of toxicity appear ideal for assessing the effects of aquatic pollutants on fish populations. Here we consider the many toxicants that disrupt complex fish behaviours, such as predator avoidance, reproductive, and social behaviours. Toxicant exposure often completely eliminates the performance of behaviours that are essential to fitness and survival in natural ecosystems, frequently after exposures of lesser magnitude than those causing significant mortality. Unfortunately, the behavioural toxicity of many xenobiotics is still unknown, warranting their future study. Physiological effects of toxicants in the literature include disruption of sensory, hormonal, neurological, and metabolic systems, which are likely to have profound implications for many fish behaviours. However, little toxicological research has sought to integrate the behavioural effects of toxicants with physiological processes. Those studies that take this multidisciplinary approach add important insight into possible mechanisms of behavioural alteration. The most commonly observed links with behavioural disruption include cholinesterase (ChE) inhibition, altered brain neurotransmitter levels, sensory deprivation, and impaired gonadal or thyroid hormone levels. Even less frequently studied are the implications of interrelated changes in behaviour and physiology caused by aquatic pollutants for fish populations. We conclude that future integrative, multidisciplinary research is clearly needed to increase the significance and usefulness of behavioural indicators for aquatic toxicology, and aim to highlight specific areas for consideration.

Butyl benzyl phthalate affects shoaling behavior and bottom-dwelling behavior in threespine stickleback

In this laboratory experiment, the effects on fish behavior caused by butyl benzyl phthalate (BBP) were of interest. We showed that shoaling behavior and bottom-dwelling behavior in threespine stickleback, Gasterosteus aculeatus, were altered as a result of exposure to 0.1 mg/L BBP. Threespine sticklebacks, collected from a freshwater population in central Norway, were exposed to BBP for 26 days. BBP was administered daily through the water. We found that exposed fish aggregated more into one single shoal than control fish. Further, the exposed fish spent more time at the bottom of the test aquarium than the control fish. From these results we conclude that the behavior traits aggregation and bottom-dwelling activity may be suitable and sensitive in detecting effects of BBP in threespine stickleback.