The utility of behavioral studies for aquatic toxicology testing: a meta-analysis

The dark side of organic farming: Copper sulphate compromises the life history and behaviour of the walking stick insect, Bacillus rossius

Organic farming is considered the most sustainable form of modern soil cultivation. Yet it often relies on the use of chemical compounds that are not necessarily harmless for the surrounding wildlife. In this study, we tested the effects of realistic concentrations of copper sulphate-largely used in organic farming as a fungicide-on ecologically-relevant traits of the walking stick insect Bacillus rossius, a species commonly found in the proximity of cultivated fields across Europe. By using second-generation progeny of wild-caught parthenogenetic females bred in common gardens, we measured the impact of copper sulphate (CuSO4) on both the life-history (body condition, number of eggs, and hatching success) and behavioural traits (activity and maximum vertical speed) of the individuals. We observed strong negative effects of high, realistic concentrations of copper sulphate on most traits within 12 days of exposure, while effects were less evident at lower concentrations of the pollutant. Our results reveal that realistic concentrations of copper sulphate can compromise important traits that regulate both the survival and reproduction of animals in the wild, with such effects that are, however, dose dependent. We suggest that common practices in organic farming require further consideration on their ecological and evolutionary impact on wildlife.

Neurobehavioral toxicity induced by combined exposure of micro/nanoplastics and triphenyltin in marine medaka (Oryzias melastigma)

Microplastics/nanoplastics (MNPs) inevitably coexist with other pollutants in the natural environment, making it crucial to study the interactions between MNPs and other pollutants as well as their combined toxic effects. In this study, we investigated neurotoxicity in marine medaka (Oryzias melastigma) exposed to polystyrene micro/nanoplastics (PS-MNPs), triphenyltin (TPT), and PS-MNPs + TPT from physiological, behavioral, biochemical, and genetic perspectives. The results showed that marine medaka exposed to 200 ng/L TPT or 200 μg/L PS-NPs alone exhibited some degree of neurodevelopmental deficit, albeit with no significant behavioral abnormalities observed. However, in the PS-MP single exposure group, the average acceleration of short-term behavioral indices was significantly increased by 78.81%, indicating a highly stress-responsive locomotor pattern exhibited by marine medaka. After exposure to PS-MNPs + TPT, the swimming ability of marine medaka significantly decreased. In addition, PS-MNPs + TPT exposure disrupted normal neural excitability as well as activated detoxification processes in marine medaka larvae. Notably, changes in neural-related genes suggested that combined exposure to PS-MNPs and TPT significantly increased the neurotoxic effects observed with exposure to PS-MNPs or TPT alone. Furthermore, compared to the PS-MPs + TPT group, PS-NPs + TPT significantly inhibited swimming behavior and thus exacerbated the neurotoxicity. Interestingly, the neurotoxicity of PS-MPs was more pronounced than that of PS-NPs in the exposure group alone. However, the addition of TPT significantly enhanced the neurotoxicity of PS-NPs compared to PS-MPs + TPT. Overall, the study underscores the combined neurotoxic effects of MNPs and TPT, providing in-depth insights into the ecotoxicological implications of MNPs coexisting with pollutants and furnishing comprehensive data.

Behavioral profile alterations and predation susceptibility of Japanese medaka fish exposed to phenytoin, an antiepileptic drug

Antiepileptic drugs, such as phenytoin, are often leaked into aquatic systems through sewage facilities due to their low metabolic rate. Fish, such as the Japanese medaka (Oryzias latipes), demonstrate abnormal swimming behavior such as equilibrium abnormalities, rotational behavior, and vertical swimming, when exposed to phenytoin. Therefore, it is hypothesized that predator avoidance may be hindered. This study aimed to investigate the effects of phenytoin exposure-induced behavioral abnormalities in predator avoidance in Japanese medaka. The results showed that individuals with behavioral abnormalities had a reduced ability to avoid danger. Furthermore, the fish demonstrated a delayed recognition reaction to approaching predators. Additionally, predatory fish, such as silver pike characin (Ctenolucius hujeta), were more likely to prey upon abnormal individuals. In conclusion, the fish exposed to phenytoin demonstrated behavioral changes that increased its predation risk. This study is the first to determine the effects of behavioral abnormalities in Japanese medaka which was induced after phenytoin exposure on predator risk avoidance.

Alteration of shoaling behavior and dysbiosis in the gut of medaka (Oryzias latipes) exposed to 2-μm polystyrene microplastics

There is global concern that microplastics may harm aquatic life. Here, we examined the effects of fine polystyrene microplastics (PS-MPs, 2-μm diameter, 0.1 mg/L, 2.5 × 107 particles/L) on the behavior and the microbiome (linked to brain-gut interaction) of a fish model using medaka, Oryzias latipes. We found that shoaling behavior was reduced in PS-MP-exposed medaka compared with control fish during the exposure period, but it recovered during a depuration period. There was no difference in swimming speed between the PS-MP-exposed and control groups during the exposure period. Analysis of the dominant bacterial population (those comprising ≥1% of the total bacterial population) in the gut of fish showed that exposure to PS-MPs tended to increase the relative abundance of the phylum Fusobacteria and the genus Vibrio. Furthermore, structural-equation modeling of gut bacteria on the basis of machine-learning data estimated strong relationship involved in the reduction of the functional bacterial species of minority (<1% of the total bacterial population) such as the genera Muribaculum (an undefined role), Aquaspirillum (a candidate for nitrate metabolism and magnetotactics), and Clostridium and Phascolarctobacterium (potential producers of short-chain fatty acids, influencing behavior by affecting levels of neurotransmitters) as a group of gut bacteria in association with PS-MP exposure. Our results suggest that fish exposure to fine microplastics may cause dysbiosis and ultimately cause social behavior disorders linked to brain-gut interactions. This effect could be connected to reduction of fish fitness in the ecosystem and reduced fish survival.

Among-individual behavioural variation in the ornamental red cherry shrimp, Neocaridina heteropoda

Personality variation, defined as among-individual differences in behaviour that are repeatable across time and context, is widely reported across animal taxa. From an evolutionary perspective, characterising the amount and structure of this variation is useful since differences among individuals are the raw material for adaptive behavioural evolution. However, behavioural variation among individuals also has implications for more applied areas of evolution and ecology-from invasion biology to ecotoxicology and selective breeding in captive systems. Here, we investigate the structure of personality variation in the red cherry shrimp, Neocaridina heteropoda, a popular ornamental species that is readily kept and bred under laboratory conditions and is emerging as a decapod crustacean model across these fields, but for which basic biological, ecological and behavioural data are limited. Using two assays and a repeated measures approach, we quantify behaviours putatively indicative of shy-bold variation and test for sexual dimorphism and/or size-dependent behaviours (as predicted by some state-dependent models of personality). We find moderate-to-high behavioural repeatabilities in most traits. Although strong individual-level correlations across behaviours are consistent with a major personality axis underlying these observed traits, the multivariate structure of personality variation does not fully match a priori expectations of a shy-bold axis. This may reflect our ecological naivety with respect to what really constitutes bolder, more risk-prone, behaviour in this species. We find no evidence for sexual dimorphism and only weak support for size-dependent behaviour. Our study contributes to the growing literature describing behavioural variation in aquatic invertebrates. Furthermore, it lays a foundation for further studies harnessing the potential of this emerging model system. In particular, this existing behavioural variation could be functionally linked to life-history traits and invasive success and serve as a target of artificial selection or bioassays. It thus holds significant promise in applied research across ecotoxicology, aquaculture and invasion biology.

Toward Real-Time Animal Tracking with Integrated Stimulus Control for Automated Conditioning in Aquatic Eco-Neurotoxicology

Aquatic eco-neurotoxicology is an emerging field that requires new analytical systems to study the effects of pollutants on animal behaviors. This is especially true if we are to gain insights into one of the least studied aspects: the potential perturbations that neurotoxicants can have on cognitive behaviors. The paucity of experimental data is partly caused by a lack of low-cost technologies for the analysis of higher-level neurological functions (e.g., associative learning) in small aquatic organisms. Here, we present a proof-of-concept prototype that utilizes a new real-time animal tracking software for on-the-fly video analysis and closed-loop, external hardware communications to deliver stimuli based on specific behaviors in aquatic organisms, spanning three animal phyla: chordates (fish, frog), platyhelminthes (flatworm), and arthropods (crustacean). The system's open-source software features an intuitive graphical user interface and advanced adaptive threshold-based image segmentation for precise animal detection. We demonstrate the precision of animal tracking across multiple aquatic species with varying modes of locomotion. The presented technology interfaces easily with low-cost and open-source hardware such as the Arduino microcontroller family for closed-loop stimuli control. The new system has potential future applications in eco-neurotoxicology, where it could enable new opportunities for cognitive research in diverse small aquatic model organisms.

The copepod Eurytemora affinis as a relevant species to assess estuarine sediment toxicity: Effects on gene expression and swimming behavior

Compared to freshwater ecosystems, the health status of estuarine waters remains little studied despite their importance for many species. They represent a zone of interest for Human settlements that make them the final sink of pollution in both the water column and sediment. Once in sediments, pollutants could represent a threat to benthic as well as pelagic estuarine species through resuspension events. In the Seine estuary, the copepod Eurytemora affinis has been previously presented as a relevant species to assess resuspended sediment contamination through fitness-related effects at the individual level. The aim of the present study was to use E. affinis copepods to assess estuarine sediment-derived elutriates toxicity at environmental concentrations of particles using a molecular (i.e. transcriptomics) and a behavioral approach. Two sites along the Seine estuary were sampled. The analysis of sediments reveals that both sites have the same granulometric composition and close contamination profiles with the detection of PCBs, PAHs and pyrethroid insecticides. The transcriptomic analysis reveals that exposure to elutriates from both sites triggers the dysregulation of genes involved in biological function as defense response, immunity, ecdysone pathway or neurotoxicity with 66% and 36% of shared genes at the highest concentration for Tancarville and Fatouville. This analysis also reveals a higher count of dysregulated genes in the Fatouville site compared to the Tancarville (271 vs 148) despite their close contamination profile. These results emphasize the molecular approach sensitivity to assess environmental matrix toxicity with E. affinis. The analysis of the swimming behavior of E. affinis did not highlight significant effects after elutriate exposure. However, our strategy to assess E. affinis swimming behavior allows the discrimination of basal swimming behavior i.e. dark/light velocity changes and strong thigmotaxis behavior. Thus, it represents a promising standardized tool to assess copepods swimming behavior in ecotoxicological studies.

Acute toxicity of tire wear particles and leachate to Daphnia magna

Tire wear particles (TWP) are a new pollutant widely present in the environment, and have been identified as microplastics (MPs), which are receiving increasing attention due to their toxic effects on aquatic organisms. In this study, D. magna was used as test organism, and the leachate from TWP was prepared by hot water extraction for 30 (30-E) and 120 min (120-E). The acute toxic effects of particles and leachate on D. magna were studied under different exposure concentrations. The results showed that zinc and pyrene were the highest detected contaminants in the leachate. The 48 h-LC50 values for particles and leachate were determined to be 56.99, 461.30 (30-E), and 153.00 mg/L (120-E), respectively. Following a 48 h exposure period, the immobilization of D. magna exposed to the particles and their leachate were increased with the concentration increase. The physical damage of the gut was found to be a possible mechanism for particle-induced biotoxicity. The compounds leached from TWP were responsible for the acute toxicity of leachate. Particles usually demonstrated a greater degree of toxicity in comparison to their leachate, especially at environmentally relevant concentrations. Exposure to particles and leachate resulted in the inhibition of swimming speed, swimming acceleration, filtration rate, and ingestion rate in D. magna. Furthermore, thoracic limb activity was observed to be inhibited. The heart rate of D. magna was significantly increased by the presence of particles at a concentration of 200 mg/L and leachate at concentrations of 400 and 800 mg/L (120-E). The observed alterations in behavior and physiological endpoints may be related to oxidative stress and neurotoxicity in the organism. Reduced superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) activities indicated that D. magna may suffer from excessive oxidative stress, whereas the increase of acetylcholinesterase (AChE) activity may serve as a biomarker of susceptibility to evaluate the environmental risks of TWP and corresponding leachates as potential aquatic pollutants.. Therefore, a more comprehensive risk assessment of TWP in the environment is necessary.

Toxicological sensitivity of protozoa to pesticides and nanomaterials: A prospect review

Protozoa are sensitive indicators of pollutant toxicity. This review presents and discusses the toxicological studies of protozoa and the toxicological conventional test species (Daphnia magna) by pesticides and nanomaterials, particularly comparing the sensitivity of through relative tolerance analysis, Z-score, and species sensitivity index. The sensitivity of different species of protozoa varies greatly. The protozoa Paramecium sp. and Tetrahymena sp. are not sensitive species; conversely, Urostyla sp. is sensitive to dimethoate and nanomaterials Ag-NPs, respectively ZnO-NPs, and CuO-NPs, fits the use as an indicator species on these substances. The prospects to explore scientific toxicity exposure protocols, expand the protozoan species examined, and screen the sensitive species under the protocols are discussed. This prospect review advances the knowledge for including the sensitive protozoa as an indicator species in comprehensive toxicological analysis for pesticides and nanomaterials.

Locomotion behavior of juveniles of the freshwater pearl mussel Margaritifera margaritifera: A new non-invasive tool for the evaluation of stress effects

The lack of knowledge about the sensitivity of the endangered freshwater pearl mussel (FWPM) Margaritifera margaritifera to environmental pollution and the rapid decline of its populations in Europe, have led to the need of developing non-destructive experimental protocols in order to assess the impact of such pollution. This species has a complex life cycle and the early life stages are considered the most sensitive. This study deals with the development of a methodology for the assessment of juvenile mussels' locomotor behavior using an automated video tracking system. Different parameters were determined such as the duration of the video recording and light exposure as a stimulus during the experiment. Locomotion behavior pattern of juveniles was assessed in control condition and also following exposure to sodium chloride as a positive control in order to validate the experimental protocol developed in this study. Results showed that juveniles locomotion behavior was stimulated under light exposure. Moreover, exposure to sublethal concentrations of sodium chloride (0.8 and 1.2 g/L) for 24 h was found to decrease juveniles' locomotion by almost three-times, thus validating our experimental methodology. This study allowed to provide a new tool for the assessment of stress condition impacts on the juveniles of the endangered FWPM, highlighting the interest of such non-destructive biomarker of health for protected species. Consequently, this will help in the improvement of our knowledge on M. margaritifera sensitivity to environmental pollution.

Factors Affecting the Adsorption of Heavy Metals by Microplastics and Their Toxic Effects on Fish

Fish not only constitute an important trophic level in aquatic ecosystems but also serve as an important source of protein for human beings. The health of fish is related to the sustained and healthy development of their entire aquatic ecosystem. Due to the widespread use, mass production, high disposal frequency, and degradation resistance of plastics, these pollutants are released into aquatic environments on a large scale. They have become one of the fastest growing pollutants and have a substantial toxic effect on fish. Microplastics have intrinsic toxicity and can absorb heavy metals discharged into water. The adsorption of heavy metals onto microplastics in aquatic environments is affected by many factors and serves as a convenient way for heavy metals to migrate from the environment to organisms. Fish are exposed to both microplastics and heavy metals. In this paper, the toxic effects of heavy metal adsorption by microplastics on fish are reviewed, and the focus is on the toxic effects at the individual (survival, feeding activity and swimming, energy reserves and respiration, intestinal microorganisms, development and growth, and reproduction), cellular (cytotoxicity, oxidative damage, inflammatory response, neurotoxicity, and metabolism) and molecular (gene expression) levels. This facilitates an assessment of the pollutants' impact on ecotoxicity and contributes to the regulation of these pollutants in the environment.

Short-term effects of an environmentally relevant concentration of organic UV filters on signal crayfish Pacifastacus leniusculus

Personal care products, including organic UV filters, are considered emerging contaminants, with their toxic effects being a concern in recent decades. UV filters continually enter surface waters via wastewater and human activity. Despite the presence of organic UV filters in the freshwater environment, little is known of their impact on aquatic biota. In this study, we evaluated the cardiac and locomotor responses of signal crayfish Pacifastacus leniusculus exposed to environmentally relevant concentrations of either 2-Phenylbenzimidazole-5-sulfonic acid (PBSA, 3 µg/L) or 5-Benzoyl-4-hydroxy-2-methoxybenzenesulfonic acid (BP4, 2.5 µg/L). Specimens exposed to the tested compounds for 30 min exhibited significantly greater changes in distance moved and time active than did unexposed controls. Significant differences of mean heart rate change compared to control were detected in both PBSA and BP4 experimental groups. Such behavior and physiological alterations demonstrate ecological effects of personal care products with the tested sunscreen compounds even with a short exposure. Evidence of the consequences of organic UV filters on aquatic organisms is scarce and is an important topic for future research.

Effects of the antidepressant fluoxetine on the swimming behaviour of the amphipod Gammarus pulex: Comparison of short-term and long-term toxicity in the laboratory and the semi-field

Fluoxetine is one of the worlds most prescribed antidepressant, and frequently detected in surface waters. Once present in the aquatic environment, fluoxetine has been shown to disrupt the swimming behaviour of fish and invertebrates. However, swimming behaviour is also known to be highly variable according to experimental conditions, potentially concealing relevant effects. Therefore, the aims of this study were two-fold: i) investigate the swimming and feeding behaviour of Gammarus pulex after exposure to the antidepressant fluoxetine (0.2, 2, 20, and 200 μg/L), and ii) assess to what degree the experimental test duration (short-term and long-term) and test location (laboratory and semi-field conditions) affect gammarid's swimming behaviour. We used automated video tracking and analysis to asses a range of swimming behaviours of G. pulex, including swimming speed, startle responses after light transition, acceleration, curvature and thigmotaxis. We found larger effects on the swimming behaviour of G. pulex due to experimental conditions than due to tested antidepressant concentrations. Gammarids swam faster, more straight and showed a stronger startle response during light transition when kept under semi-field conditions compared to the laboratory. Effects found for different test durations were opposite in the laboratory and semi-field. In the laboratory gammarids swam slower and spent more time at the inner zone of the arena after 2 days compared to 21 days while for the semi-field the reverse was observed. Fluoxetine had only minor impacts on the swimming behaviour of G. pulex, but experimental conditions influenced behavioural outcomes in response to fluoxetine exposure. Overall, our results highlight the importance of standardizing and optimizing experimental protocols that assess behaviour to achieve reproducible results in ecotoxicology.

Combined methods elucidate the multi-organ toxicity of cylindrospermopsin (CYN) on Daphnia magna

Global water bodies are now at risk from inevitable cyanobacterial blooms and their production of multiple cyanotoxins, in particular cylindrospermopsin (CYN). However, research on the CYN toxicity and its molecular mechanisms is still limited, whilst the responses of aquatic species against CYN are uncovered. By integrating behavioral observations, chemical detections and transcriptome analysis, this study demonstrated that CYN exerted multi-organ toxicity to model species, Daphnia magna. The present study confirmed that CYN could cause protein inhibition by undermining total protein contents, and altered the gene expression related to proteolysis. Meantime, CYN induced oxidative stress by increasing reactive oxygen species (ROS) level, decreasing the glutathione (GSH) concentration, and interfered with protoheme formation process molecularly. Neurotoxicity led by CYN was solidly determined by abnormal swimming patterns, reduced acetylcholinesterase (AChE), and downward expression of muscarinic acetylcholine receptor (CHRM). Importantly, for the first time, this research determined CYN directly interfered with energy metabolism in cladocerans. CYN distinctively reduced filtration and ingestion rate by targeting on heart and thoracic limbs, which declined the energy intake, and could be further displayed by the reduction of motional strength and the trypsin concentration. These phenotypic alterations were supported by transcriptomic profile, including the down-regulation of oxidative phosphorylation and ATP synthesis. Moreover, CYN was speculated to trigger the self-defense responses of D. magna, known as "abandon-ship" by moderating lipid metabolism and distribution. This study, overall, comprehensively demonstrated the CYN toxicity and the responses of D. magna against it, which is of great significance to the advancements of CYN toxicity knowledge.

Response of Parasite Community Composition to Aquatic Pollution in Common Carp (Cyprinus carpio L.): A Semi-Experimental Study

The response of parasite communities to aquatic contamination has been shown to vary with both type of pollutant and parasite lifestyle. In this semi-experimental study, we examined uptake of pharmaceutical compounds in common carp (Cyprinus carpio L.) restocked from a control pond to a treatment pond fed with organic pollution from a sewage treatment plant and assessed changes in parasite community composition and fish biometric parameters. The parasite community of restocked fish changed over the six-month exposure period, and the composition of pharmaceutical compounds in the liver and brain was almost the same as that in fish living in the treatment pond their whole life. While fish size and weight were significantly higher in both treatment groups compared to the control, condition indices, including condition factor, hepatosomatic index, and splenosomatic index, were significantly higher in control fish. Parasite diversity and species richness decreased at the polluted site, alongside a significant increase in the abundance of a single parasite species, Gyrodactylus sprostonae. Oviparous monogeneans of the Dactylogyridae and Diplozoidae families and parasitic crustaceans responded to pollution with a significant decrease in abundance, the reduction in numbers most likely related to the sensitivity of their free-living stages to pollution.

Swimming behaviour as an alternative endpoint to assess differences in abiotic stress sensitivities between strains of Brachionus koreanus (Rotifera: Monogononta)

Brachionus plicatilis is a cosmopolitan rotifer used as a model organism in several research areas and as live food in aquaculture. Being a species complex, responses to stressors vary even among strains of the same species and, thus, the responses of one species are not representative of the whole complex. This study aimed to address the effects of extreme salinity ranges, and different concentrations of hydrogen peroxide, copper, cadmium, and chloramphenicol, in two strains of B. koreanus (MRS10 and IBA3) from B. plicatilis species complex, by assessing effects on their survival and swimming capacity. Neonates (0-4 h old) were exposed to the stressors in 48 well-microplates, for 24 and 6 h, to evaluate lethal and behavioural effects, respectively. Tested conditions of chloramphenicol did not show any effects on rotifers. The behavioural endpoint showed to be particularly sensitive to assess the effects of high salinity, hydrogen peroxide, and copper sulfate, as swimming capacity impairment was observed for both strains in the lowest concentrations used in lethal tests. Overall, results showed that IBA3 was more tolerant to the majority of stressors, comparing to MRS10, which may be due to differences in physiological characteristics, highlighting the importance of performing multiclonal experiments. Also, swimming capacity inhibition proved to be a good alternative to the classical lethality tests, being sensitive to lower concentrations and with shorter exposure periods.

Effects of 17α-ethinylestradiol on the neuroendocrine gonadotropic system and behavior of European sea bass larvae (Dicentrarchus labrax)

The widespread use of 17α-ethinylestradiol (EE2), and other estrogenic endocrine disruptors, results in a continuous release of estrogenic compounds into aquatic environments. Xenoestrogens may interfere with the neuroendocrine system of aquatic organisms and may produce various adverse effects. The aim of the present study was to expose European sea bass larvae (Dicentrarchus labrax) to EE2 (0.5 and 50 nM) for 8 d and determine the expression levels of brain aromatase (cyp19a1b), gonadotropin-releasing hormones (gnrh1, gnrh2, gnrh3), kisspeptins (kiss1, kiss2) and estrogen receptors (esr1, esr2a, esr2b, gpera, gperb). Growth and behavior of larvae as evidenced by locomotor activity and anxiety-like behaviors were measured 8 d after EE2 treatment and a depuration period of 20 d. Exposure to 0.5 nM EE2 induced a significant increase in cyp19a1b expression levels, while upregulation of gnrh2, kiss1, and cyp19a1b expression was noted after 8 d at 50 nM EE2. Standard length at the end of the exposure phase was significantly lower in larvae exposed to 50 nM EE2 than in control; however, this effect was no longer observed after the depuration phase. The upregulation of gnrh2, kiss1, and cyp19a1b expression levels was found in conjunction with elevation in locomotor activity and anxiety-like behaviors in larvae. Behavioral alterations were still detected at the end of the depuration phase. Evidence indicates that the long-lasting effects of EE2 on behavior might impact normal development and subsequent fitness of exposed fish.

Exposure to the persistent organic pollutant 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD, dioxin) disrupts development of the zebrafish inner ear

Dioxins are a class of highly toxic and persistent environmental pollutants that have been shown through epidemiological and laboratory-based studies to act as developmental teratogens. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most potent dioxin congener, has a high affinity for the aryl hydrocarbon receptor (AHR), a ligand activated transcription factor. TCDD-induced AHR activation during development impairs nervous system, cardiac, and craniofacial development. Despite the robust phenotypes previously reported, the characterization of developmental malformations and our understanding of the molecular targets mediating TCDD-induced developmental toxicity remains limited. In zebrafish, TCDD-induced craniofacial malformations are produced, in part, by the downregulation of SRY-box transcription factor 9b ( sox9b ), a member of the SoxE gene family. sox9b , along with fellow SoxE gene family members sox9a and sox10 , have important functions in the development of the otic placode, the otic vesicle, and, ultimately, the inner ear. Given that sox9b in a known target of TCDD and that transcriptional interactions exist among SoxE genes, we asked whether TCDD exposure impaired the development of the zebrafish auditory system, specifically the otic vesicle, which gives rise to the sensory components of the inner ear. Using immunohistochemistry, in vivo confocal imaging, and time-lapse microscopy, we assessed the impact of TCDD exposure on zebrafish otic vesicle development. We found exposure resulted in structural deficits, including incomplete pillar fusion and altered pillar topography, leading to defective semicircular canal development. The observed structural deficits were accompanied by reduced collagen type II expression in the ear. Together, our findings reveal the otic vesicle as a novel target of TCDD-induced toxicity, suggest that the function of multiple SoxE genes may be affected by TCDD exposure, and provide insight into how environmental contaminants contribute to congenital malformations.

Highlights

The zebrafish ear is necessary to detect changes in motion, sound, and gravity.Embryos exposed to TCDD lack structural components of the developing ear.TCDD exposure impairs formation of the fusion plate and alters pillar topography.The semicircular canals of the ear are required to detect changes in movement.Following TCDD exposure embryos fail to establish semicircular canals.

Swimming Behavior of Daphnia magna Is Altered by Pesticides of Concern, as Components of Agricultural Surface Water and in Acute Exposures

Pesticides with novel modes of action including neonicotinoids and anthranilic diamides are increasingly detected in global surface waters. Little is known about how these pesticides of concern interact in mixtures at environmentally relevant concentrations, a common exposure scenario in waterways impacted by pesticide pollution. We examined effects of chlorantraniliprole (CHL) and imidacloprid (IMI) on the sensitive invertebrate, Daphnia magna. Exposures were first performed using surface waters known to be contaminated by agricultural runoff. To evaluate the seasonal variation in chemical concentration and composition of surface waters, we tested surface water samples taken at two time points: during an extended dry period and after a first flush storm event. In surface waters, the concentrations of CHL, IMI, and other pesticides of concern increased after first flush, resulting in hypoactivity and dose-dependent photomotor responses. We then examined mortality and behavior following single and binary chemical mixtures of CHL and IMI. We detected inverse photomotor responses and some evidence of synergistic effects in binary mixture exposures. Taken together, this research demonstrates that CHL, IMI, and contaminated surface waters all cause abnormal swimming behavior in D. magna. Invertebrate swimming behavior is a sensitive endpoint for measuring the biological effects of environmental pesticides of concern.

Previous stress causes a contrasting response to cadmium toxicity in the aquatic snail Potamopyrgus antipodarum: lethal and behavioral endpoints

In aquatic ecosystems, animals are often exposed to a combination of stressors, including both natural and anthropogenic factors. Combined stressors may have additive or interactive effects on animals, either magnifying or reducing the effects caused by each stressor alone. Therefore, standardized bioassays can lead to overestimations or underestimations of the risk of toxicants if natural stressors are not bear in mind. The inclusion of natural stress in laboratory bioassays may help to extrapolate the laboratory results to ecosystems. This study assesses the effects of successive exposure to two sources of stress (high water conductivity and cadmium toxicity) on the behavior and survival of the aquatic snail Potamopyrgus antipodarum (Tateidae, Mollusca). I conducted a bioassay consisting on exposure to high conductivity (5000 mg NaCl/L, 7 days), followed by exposure to cadmium (0.03, 0.125, and 0.25 mg Cd/L for 7 days) and by a post-exposure period (7 days). Mortality, inactivity, and the time to start activity of active animals were monitored in each animal. In general, cadmium lethality was higher in animals previously undergoing high conductivity than in non-stressed ones. Previously stressed animals showed longer time to start activity, with a noticeable effect at the two highest cadmium concentrations. Animals submitted to the two highest cadmium concentration both, stressed and non-stressed, showed a moderate recovery during the post-exposure period. It is concluded that previous stress caused a worsening of the cadmium toxicity on the aquatic snail Potamopyrgus antipodarum, which is especially noticeable for mortality. However, there was no interactive effect between cadmium and conductivity on snail activity, which may be indicative of recovery after cadmium exposure regardless the previous stress suffered by the snails.

Post-exposure Period as a key Factor to Assess Cadmium Toxicity: Lethal vs. Behavioral Responses

The exposure of animals to pollution in ecosystems is not always chronic. Toxicants can remain in aquatic ecosystems for a short-term. To improve the extrapolation of laboratory results to natural scenarios the inclusion of post-exposure periods is a relevant issue. The present study focuses on the assessment of cadmium toxicity on survival and behavior of the aquatic snail Potamopyrgus antipodarum (Tateidae, Mollusca) during exposure and post-exposure. Animals were exposed for 48 h to cadmium (0.05, 0.14, 0.44 and 1.34 mg Cd/L) and 168 h of post-exposure. During the post-exposure period an increase in mortality in all concentrations was observed. The effects observed during the post-exposure period on the LC50 and EC50 were significant. During the post-exposure, behavior showed a clear recovery in surviving animals exposed to 0.44 mg Cd/L. Animals exposed to 0.05 mg Cd/L did not show differences with control. Therefore, mortality after exposure should be included in the ecotoxicological bioassays for a more realistic estimation of the cadmium effects. To assess the degree of animal recovery after cadmium exposure, behaviour has been shown as an adequate parameter.

Neuroactive pharmaceuticals in estuaries: Occurrence and tissue-specific bioaccumulation in multiple fish species

Contamination of surface waters by pharmaceuticals is an emerging problem globally. This is because the increased access and use of pharmaceuticals by a growing world population lead to environmental contamination, threatening non-target species in their natural environment. Of particular concern are neuroactive pharmaceuticals, which are known to bioaccumulate in fish and impact a variety of individual processes such as fish reproduction or behaviour, which can have ecological impacts and compromise fish populations. In this work, we investigate the occurrence and bioaccumulation of 33 neuroactive pharmaceuticals in brain, muscle and liver tissues of multiple fish species collected in four different estuaries (Douro, Tejo, Sado and Mira). In total, 28 neuroactive pharmaceuticals were detected in water and 13 in fish tissues, with individual pharmaceuticals reaching maximum concentrations of 1590 ng/L and 207 ng/g ww, respectively. The neuroactive pharmaceuticals with the highest levels and highest frequency of detection in the water samples were psychostimulants, antidepressants, opioids and anxiolytics, whereas in fish tissues, antiepileptics, psychostimulants, anxiolytics and antidepressants showed highest concentrations. Bioaccumulation was ubiquitous, occurring in all seven estuarine and marine fish species. Notably, neuroactive compounds were detected in every water and fish brain samples, and in 95% of fish liver and muscle tissues. Despite variations in pharmaceutical occurrence among estuaries, bioaccumulation patterns were consistent among estuarine systems, with generally higher bioaccumulation in fish brain followed by liver and muscle. Moreover, no link between bioaccumulation and compounds' lipophilicity, species habitat use patterns or trophic levels was observed. Overall, this work highlights the occurrence of a highly diverse suite of neuroactive pharmaceuticals and their pervasiveness in waters and fish from estuarine systems with contrasting hydromorphology and urban development and emphasizes the urgent need for toxicity assessment of these compounds in natural ecosystems, linked to internalized body concentration in non-target species.

Cuttlefish color change as an emerging proxy for ecotoxicology

Lately, behavioral ecotoxicology has flourished because of increasing standardization of analyses of endpoints like movement. However, research tends to focus on a few model species, which limits possibilities of extrapolating and predicting toxicological effects and adverse outcomes at the population and ecosystem level. In this regard, it is recommended to assess critical species-specific behavioral responses in taxa playing key roles in trophic food webs, such as cephalopods. These latter, known as masters of camouflage, display rapid physiological color changes to conceal themselves and adapt to their surrounding environments. The efficiency of this process depends on visual abilities and acuity, information processing, and control of chromatophores dynamics through nervous and hormonal regulation with which many contaminants can interfere. Therefore, the quantitative measurement of color change in cephalopod species could be developed as a powerful endpoint for toxicological risk assessment. Based on a wide body of research having assessed the effect of various environmental stressors (pharmaceutical residues, metals, carbon dioxide, anti-fouling agents) on the camouflage abilities of juvenile common cuttlefish, we discuss the relevance of this species as a toxicological model and address the challenge of color change quantification and standardization through a comparative review of the available measurement techniques.

Daphnia as a model organism to probe biological responses to nanomaterials-from individual to population effects via adverse outcome pathways

The importance of the cladoceran Daphnia as a model organism for ecotoxicity testing has been well-established since the 1980s. Daphnia have been increasingly used in standardised testing of chemicals as they are well characterised and show sensitivity to pollutants, making them an essential indicator species for environmental stress. The mapping of the genomes of D. pulex in 2012 and D. magna in 2017 further consolidated their utility for ecotoxicity testing, including demonstrating the responsiveness of the Daphnia genome to environmental stressors. The short lifecycle and parthenogenetic reproduction make Daphnia useful for assessment of developmental toxicity and adaption to stress. The emergence of nanomaterials (NMs) and their safety assessment has introduced some challenges to the use of standard toxicity tests which were developed for soluble chemicals. NMs have enormous reactive surface areas resulting in dynamic interactions with dissolved organic carbon, proteins and other biomolecules in their surroundings leading to a myriad of physical, chemical, biological, and macromolecular transformations of the NMs and thus changes in their bioavailability to, and impacts on, daphnids. However, NM safety assessments are also driving innovations in our approaches to toxicity testing, for both chemicals and other emerging contaminants such as microplastics (MPs). These advances include establishing more realistic environmental exposures via medium composition tuning including pre-conditioning by the organisms to provide relevant biomolecules as background, development of microfluidics approaches to mimic environmental flow conditions typical in streams, utilisation of field daphnids cultured in the lab to assess adaption and impacts of pre-exposure to pollution gradients, and of course development of mechanistic insights to connect the first encounter with NMs or MPs to an adverse outcome, via the key events in an adverse outcome pathway. Insights into these developments are presented below to inspire further advances and utilisation of these important organisms as part of an overall environmental risk assessment of NMs and MPs impacts, including in mixture exposure scenarios.

Morphological and behavioral alterations in zebrafish larvae after exposure to contaminated river sediments collected in different weather conditions

Wastewater treatment plants (WWTPs) are the primary source of micropollutants in aquatic ecosystems. Many micropollutants tend to bind to sediments and persist until remobilizion by bioturbation or flood events. Advanced effluent treatment by ozonation has been proven to eliminate most micropollutants. The present study characterizes sediments' toxic potential regarding zebrafish embryo development, which highly complex nervous system is vulnerable to exposure to neurotoxic substances. Furthermore, behavioral changes can be induced even at low pollutant concentrations and do not cause acute toxicity. The study area includes stretches of the main waterbody, the Wurm River (sampling sites W1-W5), and its tributary the Haarbach River (sampling sites H1, and H2) in North-Rhine Westphalia, Germany. Both waterbodies serve as recipients of WWTPs' effluents. The effluent entering the Haarbach River is conventionally treated, while the Wurm River receives ozonated effluent from the Aachen-Soers WWTP. Seven sampling sites up- and downstream of the WWTPs were investigated in June of two subsequent years. The first sampling campaign in 2017 was characterized by prolonged dry weather. The second sampling campaign in 2018 occurred after prolonged rain events and the release of the rainwater overflow basin. Direct exposure of zebrafish embryos to native sediments using the sediment contact test represented an ecologically realistic scenario and showed no acute sublethal effects. Exposure of the zebrafish embryo to freeze-dried sediments representing the ecotoxicological status of sediments during flood events unfolded acute sublethal toxicity. Behavioral studies with zebrafish larvae were an essential part of environmental neurotoxicity testing. Zebrafish larvae exposed to sediments' concentrations causing no acute effects led to behavioral changes signalizing neurotoxic substances in sediments. Polyaromatic hydrocarbons, polychlorinated biphenyls, and nitroaromatic compounds were identified as potential toxicity drivers, whereby the rainwater overflow basin served as a possible source of pollution. Mixture toxicity, effect-directed analysis, and further sediment monitoring are needed.

Assessment of the exposure of two pesticides on common carp (Cyprinus carpio Linnaeus, 1758): Are the prolonged biomarker responses adaptive or destructive?

Chlorpyrifos (CPF) and cypermethrin (CYP) are two insecticides that have a proven negative effect on non-target aquatic organisms when they enter the surface waters. However, literature on the comparative effects of these pesticides on important aquaculture fish species, such as common carp (Cyprinus carpio Linnaeus, 1758) is not yet scientifically detailed, especially over the long-term. The idea of conducting a long-term exposure is to find out how the observed biomarkers would change compared to the short-term exposure. In the natural environment, toxicants are not present alone, but in combination. By monitoring the long-term impact of individual substances, the state of aquatic ecosystems exposed to various toxicants could be predicted. Thus, this study aimed to evaluate the toxicity of different concentrations of CYP (0.0002, 0.0003, and 0.0006 μg/L) and CPF (0.03, 0.05, and 0.10 μg/L) in 50-L glass tanks on C. carpio, exposed for 30 days under laboratory conditions. A set of histological and biochemical biomarkers in the gills and liver were applied with the chemical analyses of water and fish organs. Furthermore, the condition and hepatosomatic index were calculated to assess the physiological status of the treated carps. The behavioral responses were also monitored, and the respiration rate was analyzed. The results suggest that CYP had a more prominent effect on the histological structure of fish organs, biochemical responses of anti-oxidant enzymes, behavior, and respiration rate compared to the effect of CPF. In addition, the results also indicate that the liver is more susceptible to chronic and chemically induced cellular stress compared to the gills, with overall destructive changes in the histological biomarkers rather than adaptive. Regardless of the scenario, our results provide novel insights into pesticide exposure and the possible biological impacts on economically important freshwater fish, exposed to lower CYP and CPF concentrations, based on the EU legislation (maximum allowable concentrations, MAC-EQS).

Differential biochemical and behavioral responses induced by cocaine and benzoylecgonine exposure to the red swamp crayfish Procambarus clarkii

Cocaine (COC) and its main metabolite, the benzoylecgonine (BE), are the main illicit drugs measured in aquatic system worldwide, with concentrations up to hundreds of ng/L. Although their current environmental concentrations are low these molecules can induce adverse effects at sub-individual level in non-target organisms. In contrast, the information at individual and behavioral level are still scant. The present study aimed at investigating biochemical and behavioral effects induced by 14-days exposure to environmentally relevant concentrations (50 ng/L and 500 ng/L) of COC and BE towards Procambarus clarkii. At sub-individual level, the activity of antioxidant and detoxifying (superoxide dismutase - SOD, catalase - CAT, glutathione peroxidase - GPx and glutathione S-transferases - GST) enzymes, as well as the levels of lipid peroxidation (LPO), were measured as oxidative stress-related endpoints. We also measured the acetylcholinesterase (AChE) activity to check for neurotoxic effect of COC and BE. At individual level, the modulation of some behavioral tasks (i.e., response to external stimuli, changes in feeding activity and exploration of a new environment) were assessed. Although both COC and BE exposure did not induce an oxidative stress situation, a significant inhibition of AChE activity was noted, resulting in behavioral changes in crayfish exposed to COC only. Crayfish exposed to the higher COC concentration showed an increase in the boldness and a decrease in the feeding activity, suggesting that COC may act according to its psychotropic mode of action.

Same sensitivity with shorter exposure: behavior as an appropriate parameter to assess metal toxicity

The exposure of animals to toxicants may cause a depletion in the energy uptake, which compromises reproduction and growth. Although both parameters are ecologically relevant, they usually need long-term bioassays. This is a handicap for the availability of toxicological data for environmental risk assessment. Short-term bioassays conducted with environmental concentrations, and using relevant ecological parameters sensitive to short-term exposures, such as behavior, could be a good alternative. Therefore, to include this parameter in the risk assessment procedures, it is relevant the comparison of its sensitivity with that of growth and reproduction bioassays. The study aim was the assessment of differences between endpoints based on mortality, behaviour, reproduction, and growth for the toxicity of metals on aquatic animals. We used the ECOTOX database to gather data to construct chemical toxicity distribution (CTD) curves. The mean concentrations, the mean exposure time, and the ratio between the mean concentration and the exposure time were compared among endpoints. Our results showed that behavioral, growth, and reproduction bioassays presented similar sensitivity. The shortest exposure was found in behavioral and reproduction bioassays. In general, the amount of toxicant used per time was lower in growth and reproduction bioassays than in behavioral and mortality bioassays. We can conclude that, for metal toxicity, behavioral bioassays are less time-consuming than growth bioassays. As the sensitivity of behavior was similar to that of growth and reproduction, this endpoint could be a better alternative to longer bioassays.

Digital Video Acquisition and Optimization Techniques for Effective Animal Tracking in Behavioral Ecotoxicology

Behavioral phenotypic analysis is an emerging and increasingly important toolbox in aquatic ecotoxicology. In this regard digital video recording has recently become a standard in obtaining behavioral data. Subsequent analysis requires applications of specialized software for detecting and reconstructing animal locomotory trajectories as well as extracting quantitative biometric endpoints associated with specific behavioral traits. Despite some profound advantages for behavioral ecotoxicology, there is a notable lack of standardization of procedures and guidelines that would aid in consistently acquiring high-quality digital videos. The latter are fundamental for using animal tracking software successfully and to avoid issues such as identification switching, incorrect interpolation, and low tracking visibility. Achieving an optimized tracking not only saves user time and effort to analyze the results but also provides high-fidelity data with minimal artifacts. In the present study we, for the first time, provide an easily accessible guide on how to set up and optimize digital video acquisition while minimizing pitfalls in obtaining the highest-quality data for subsequent animal tracking. We also discuss straightforward digital video postprocessing techniques that can be employed to further enhance tracking consistency or improve the videos that were acquired in otherwise suboptimal settings. The present study provides an essential guidebook for any aquatic ecotoxicology studies that utilize digital video acquisition systems for evaluation of behavioral endpoints. Environ Toxicol Chem 2022;41:2342-2352. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Effects of the agricultural pollutant 17β-trenbolone on morphology and behaviour of tadpoles (Limnodynastes tasmaniensis)

Pollutants, such as endocrine disrupting chemicals (EDCs), are increasingly being detected in organisms and ecosystems globally. Agricultural activities, including the use of hormonal growth promotants (HGPs), are a major source of EDC contamination. One potent EDC that enters into the environment through the use of HGPs is 17β-trenbolone. Despite EDCs being repeatedly shown to affect reproduction and development, comparatively little is known regarding their effects on behaviour. Amphibians, one of the most imperilled vertebrate taxa globally, are at particular risk of exposure to such pollutants as they often live and breed near agricultural operations. Yet, no previous research on amphibians has explored the effects of 17β-trenbolone exposure on foraging or antipredator behaviour, both of which are key fitness-related behavioural traits. Accordingly, we investigated the impacts of 28-day exposure to two environmentally realistic concentrations of 17β-trenbolone (average measured concentrations: 10 and 66 ng/L) on the behaviour and growth of spotted marsh frog tadpoles (Limnodynastes tasmaniensis). Contrary to our predictions, there was no significant effect of 17β-trenbolone exposure on tadpole growth, antipredator response, anxiety-like behaviour, or foraging. We hypothesise that the differences in effects found between this study and those conducted on fish may be due to taxonomic differences and/or the life stage of the animals used, and suggest further research is needed to investigate the potential for delayed manifestation of the effects of 17β-trenbolone exposure.

Cyclophosphamide alters the behaviors of adult Zebrafish via neurotransmitters and gut microbiota

Cyclophosphamide, one of the earliest prescribed alkylating anticancer drugs, has been frequently detected in aquatic environments. However, its effects on fish behavior and associated mechanisms remain largely unknown. In this study, the behaviors, neurochemicals, and gut microbiota of adult zebrafish were investigated after 2 months of exposure to CP at 0.05, 0.5, 5, and 50 µg/L. Behavioral assays revealed that CP increased locomotion and anxiety, and decreased the cognition of zebrafish. The alteration of neurotransmitters and related gene expressions in the dopamine and gamma-aminobutyric acid pathways induced by CP may be responsible for the observed changes in locomotion and cognition of adult zebrafish. Meanwhile, CP increased the anxiety of adult zebrafish through the serotonin, acetylcholine, and histamine pathways in the brain. In addition, increased abundances of Fusobacteriales, Reyanellales, Staphylococcales, Rhodobacterals, and Patescibateria in the intestine at the CP-50 treatment were observed. The study has demonstrated that CP affects the locomotion, anxiety, and cognition in zebrafish, which might be linked with the dysfunction of neurochemicals in the brain. This study further suggests that the gut-brain axis might interact to modulate fish behaviors upon exposure to CP (maybe other organic pollutants). Further research is warranted to test this hypothesis.

Toxic effects of glyphosate on the intestine, liver, brain of carp and on epithelioma papulosum cyprinid cells: Evidence from in vivo and in vitro research

Glyphosate (GLY) is the most widely used organophosphorus herbicide in agriculture. The present study aimed to analyze the comprehensive toxicological effects of GLY on juvenile common carp and an epithelioma papulosum cyprinid (EPC) cell line. In the in vivo experiments, exposure to GLY (5 and 15 mg/L) for 30 days induced liver inflammation and oxidative damage in common carp and changed the physical barrier of the intestine. Histopathological analysis of the intestine, liver, brain, and changes in oxidative stress biomarkers provided evidence of damage and immune system responses to GLY. Moreover, an inhibitory effect of 15 mg/L GLY on acetylcholinesterase (AChE) activity was found in the brain, which may be an important reason for the significant decrease in both swimming distance and average acceleration of common carp. Cell experiments showed that 0.65 and 3.25 mg/L GLY inhibited the viability of EPCs. Furthermore, oxidative DNA damage, mitochondrial dysfunction, and reactive oxygen species (ROS) production were observed in EPC cells following GLY exposure. Taken together, this study not only highlights the negative effects of GLY on common carp but also enriches the knowledge of the cytotoxicity mechanism to further clarify the comprehensive toxicity of GLY in common carp.

Evaluation of Locomotion Complexity in Zebrafish after Exposure to Twenty Antibiotics by Fractal Dimension and Entropy Analysis

Antibiotics are extensively used in aquaculture to prevent bacterial infection and the spread of diseases. Some antibiotics have a relatively longer half-life in water and may induce some adverse effects on the targeted fish species. This study analyzed the potential adverse effects of antibiotics in zebrafish at the behavioral level by a phenomic approach. We conducted three-dimensional (3D) locomotion tracking for adult zebrafish after acute exposure to twenty different antibiotics at a concentration of 100 ppb for 10 days. Their locomotor complexity was analyzed and compared by fractal dimension and permutation entropy analysis. The dimensionality reduction method was performed by combining the data gathered from behavioral endpoints alteration. Principal component and hierarchical analysis conclude that three antibiotics: amoxicillin, trimethoprim, and tylosin, displayed unique characteristics. The effects of these three antibiotics at lower concentrations (1 and 10 ppb) were observed in a follow-up study. Based on the results, these antibiotics can trigger several behavioral alterations in adult zebrafish, even in low doses. Significant changes in locomotor behavioral activity, such as total distance activity, average speed, rapid movement time, angular velocity, time in top/bottom duration, and meandering movement are highly related to neurological motor impairments, anxiety levels, and stress responses were observed. This study provides evidence based on an in vivo experiment to support the idea that the usage of some antibiotics should be carefully addressed since they can induce a significant effect of behavioral alterations in fish.

Frontiers in quantifying wildlife behavioural responses to chemical pollution

Animal behaviour is remarkably sensitive to disruption by chemical pollution, with widespread implications for ecological and evolutionary processes in contaminated wildlife populations. However, conventional approaches applied to study the impacts of chemical pollutants on wildlife behaviour seldom address the complexity of natural environments in which contamination occurs. The aim of this review is to guide the rapidly developing field of behavioural ecotoxicology towards increased environmental realism, ecological complexity, and mechanistic understanding. We identify research areas in ecology that to date have been largely overlooked within behavioural ecotoxicology but which promise to yield valuable insights, including within- and among-individual variation, social networks and collective behaviour, and multi-stressor interactions. Further, we feature methodological and technological innovations that enable the collection of data on pollutant-induced behavioural changes at an unprecedented resolution and scale in the laboratory and the field. In an era of rapid environmental change, there is an urgent need to advance our understanding of the real-world impacts of chemical pollution on wildlife behaviour. This review therefore provides a roadmap of the major outstanding questions in behavioural ecotoxicology and highlights the need for increased cross-talk with other disciplines in order to find the answers.

Identifying Behavioral Response Profiles of Two Common Larval Fish Models to a Salinity Gradient

Salinization of aquatic systems is an emerging global issue projected to increase in magnitude, frequency, and duration with climate change and landscape modifications. To consider influences of salinity on locomotor activity of common fish models, we examined behavioral response profiles of two species, zebrafish (Danio rerio) and fathead minnow (Pimephales promelas), across a gradient of sodium chloride. Following each experiment, behavior was recorded with automated tracking software and then behavioral response variables, including locomotor (e.g., distance traveled, number of movements, duration of movements) and photolocomotor changes, were examined at several speed thresholds (bursting, cruising, freezing) to identify potential salinity responses. Zebrafish responses were significantly (p < 0.05) reduced at the highest treatment level (5.78 g/L) for multiple behavioral endpoints during both dark and light phases; however, fathead minnow responses were more variable and not consistently concentration dependent. Future efforts are needed to understand behavioral response profiles in combination with anthropogenic contaminants and natural toxins across the freshwater to marine continuum, considering salinization of inland waters, sea level rise, and transport of anthropogenic contaminants and algal toxins from inland waters to coastal systems.

Fish Behavior as a Neural Proxy to Reveal Physiological States

Behaviors are the integrative outcomes of the nervous system, which senses and responds to the internal physiological status and external stimuli. Teleosts are aquatic organisms which are more easily affected by the surrounding environment compared to terrestrial animals. To date, behavioral tests have been widely used to assess potential environmental risks using fish as model animals. In this review, we summarized recent studies regarding the effects of internal and external stimuli on fish behaviors. We concluded that behaviors reflect environmental and physiological changes, which have possible implications for environmental and physiological assessments.

Beyond the behavioural phenotype: Uncovering mechanistic foundations in aquatic eco-neurotoxicology

During the last decade, there has been an increase in awareness of how anthropogenic pollution can alter behavioural traits of diverse aquatic organisms. Apart from understanding profound ecological implications, alterations in neuro-behavioural indices have emerged as sensitive and physiologically integrative endpoints in chemical risk assessment. Accordingly, behavioural ecotoxicology and broader eco-neurotoxicology are becoming increasingly popular fields of research that span a plethora of fundamental laboratory experimentations as well as applied field-based studies. Despite mounting interest in aquatic behavioural ecotoxicology studies, there is, however, a considerable paucity in deciphering the mechanistic foundations underlying behavioural alterations upon exposure to pollutants. The behavioural phenotype is indeed the highest-level integrative neurobiological phenomenon, but at its core lie myriads of intertwined biochemical, cellular, and physiological processes. Therefore, the mechanisms that underlie changes in behavioural phenotypes can stem among others from dysregulation of neurotransmitter pathways, electrical signalling, and cell death of discrete cell populations in the central and peripheral nervous systems. They can, however, also be a result of toxicity to sensory organs and even metabolic dysfunctions. In this critical review, we outline why behavioural phenotyping should be the starting point that leads to actual discovery of fundamental mechanisms underlying actions of neurotoxic and neuromodulating contaminants. We highlight potential applications of the currently existing and emerging neurobiology and neurophysiology analytical strategies that should be embraced and more broadly adopted in behavioural ecotoxicology. Such strategies can provide new mechanistic discoveries instead of only observing the end sum phenotypic effects.

The Influence of the Recording Time in Modelling the Swimming Behaviour of the Freshwater Inbenthic Copepod Bryocamptus pygmaeus

The analysis of copepod behaviour gained an increasing impetus over the past decade thanks to the advent of computer-assisted video analysis tools. Since the automated tracking consists in detecting the animal’s position frame by frame and improving signals corrupted by strong background noise, a crucial role is played by the length of the video recording. The aim of this study is to: (i) assess whether the recording time influences the analysis of a suite of movement descriptive parameters; (ii) understand if the recording time influences the outcome of the statistical analyses when hypotheses on the effect of toxicants/chemicals on the freshwater invertebrate behaviour are tested. We investigated trajectory parameters commonly used in behavioural studies—swimming speed, percentage of activity and trajectory convex hull—derived from the trajectories described by the inbenthic–interstitial freshwater copepod Bryocamptus pygmaeus exposed to a sub-lethal concentration of diclofenac. The analyses presented in this work indicate that the recording time did not influence the outcome of the results for the swimming speed and the percentage of activity. For the trajectory convex hull area, our results showed that a recording session lasting at least 3 min provided robust results. However, further investigations are needed to disentangle the role of concurrent factors, such as the behavioural analysis of multiple individuals simultaneously, whether they are of the same or opposite sex and the implications on sexual behaviour, competition for resources and predation.

Acute Toxicity Evaluation of the Disinfectant Containing Percarbonate and Tetraacetylethylenediamine by Measuring Behavioral Responses of Small Fish Using Image Analysis

Disinfectants containing percarbonate and tetraacetylethylenediamine (TAED) has been developed as an effective and relatively safe disinfectant to destroy viruses and bacteria in animals and humans, however it is known that most disinfectants can cause danger to living organisms including humans. In the current study, acute toxicity of the disinfectant composed of percarbonate and TAED was assessed by measuring behavioral responses as well as lethal concentrations of aquatic organisms such as medaka and zebrafish when they were exposed to it. First, the breeding water properties were determined by measuring dissolved oxygen (DO) and pH changes over time up to 96 h in acute toxicity tests using the medaka, and the lethal concentration 50% (LC50, 88.39 ppm) was calculated using the lethality rate of the fish. This experiment was conducted in compliance with traditional OECD guidelines. Second, the assessment of behavioral responses (locomotive activity and swimming speed) with the zebrafish were assessed by the image analysis to capture the images per second for three hours, and the collected data were processed using image analysis to calculate the locomotive activity and swimming speed. Finally, the LC50 (135.76 ppm) of the disinfectant to the fish was also measured after three hours. Overall, the data revealed that LC50 of the disinfectant may be affected by the pH of the water exposed to the disinfectant, not by the DO in the water. In addition, the results from the image analysis indicated that the behavioral responses of the fish can further assess the acute toxicity of the disinfectant at concentrations below the LC50 and there was a relationship (R² = 0.85) between the behavioral responses and the survival rate of the fish.

Behavioral Variables to Assess the Toxicity of Unionized Ammonia in Aquatic Snails: Integrating Movement and Feeding Parameters

Behavioral endpoints are important parameters to assess the effects of toxicants on aquatic animals. These endpoints are useful in ecotoxicology because several toxicants modify the animal behavior, which may cause adverse effects at higher levels of ecological organization. However, for the development of new bioassays and for including the behavior in ecotoxicological risk assessment, the comparison of sensitivity between different behavioral endpoints is necessary. Additionally, some toxicants remain in aquatic environments for a few hours or days, which may lead to animal recovery after toxicant exposure. Our study aimed to assess the effect of unionized ammonia on the movement and feeding behaviors of the aquatic gastropod Potamopyrgus antipodarum (Tateidae, Mollusca) and its recovery after exposure. Four treatments were used: a control and three nominal concentrations of unionized ammonia (0.25, 0.5 and 1 mg N-NH₃/L). Each treatment was replicated eight times, with six animals in each replicate. Animals were exposed to unionized ammonia for 48 h (exposure period) and, subsequently, to control water for 144 h (post-exposure period). Two movement variables were monitored without food and five feeding behavioral variables were monitored in the presence of food. Some of the feeding behavioral variables showed higher sensitivity (LOEC = 0.25-0.5 mg N-NH₃/L) than the movement behavior variables monitored without food (LOEC = 1 mg N-NH₃/L). After exposure to unionized ammonia, animals showed a recovery of most behavioral endpoints. The inclusion of post-exposure period and feeding behaviors in bioassays may make studies more realistic, which is crucial for a proper ecotoxicological risk assessment.

Microplastics and Their Impact on Reproduction—Can we Learn From the C. elegans Model?

Biologically active environmental pollutants have significant impact on ecosystems, wildlife, and human health. Microplastic (MP) and nanoplastic (NP) particles are pollutants that are present in the terrestrial and aquatic ecosystems at virtually every level of the food chain. Moreover, recently, airborne microplastic particles have been shown to reach and potentially damage respiratory systems. Microplastics and nanoplastics have been shown to cause increased oxidative stress, inflammation, altered metabolism leading to cellular damage, which ultimately affects tissue and organismal homeostasis in numerous animal species and human cells. However, the full impact of these plastic particles on living organisms is not completely understood. The ability of MPs/NPs to carry contaminants, toxic chemicals, pesticides, and bioactive compounds, such as endocrine disrupting chemicals, present an additional risk to animal and human health. This review will discusses the current knowledge on pathways by which microplastic and nanoplastic particles impact reproduction and reproductive behaviors from the level of the whole organism down to plastics-induced cellular defects, while also identifying gaps in current knowledge regarding mechanisms of action. Furthermore, we suggest that the nematode Caenorhabditis elegans provides an advantageous high-throughput model system for determining the effect of plastic particles on animal reproduction, using reproductive behavioral end points and cellular readouts.

Bioconcentration of neuroactive pharmaceuticals in fish: Relation to lipophilicity, experimental design and toxicity in the aquatic environment

Uptake of contaminants is linked to their toxicity and is usually estimated through their lipophilicity (logK_ow). Here, we review current literature regarding bioconcentration, i.e. uptake of contaminants from the external environment only, and the effects of exposure to neuroactive pharmaceuticals in fish. We aim to determine if lipophilicity is a suitable predictor of bioconcentration of these compounds in fish, to identify major drivers of bioconcentration and explore the link between bioconcentration potential and toxicity, focusing on survival, growth, condition, behaviour and reproduction endpoints. Additionally, we compare concentrations known to elicit significant effects in fish with current environmental concentrations, identifying exposure risk in ecosystems. The majority of studies have focused on antidepressants, mainly fluoxetine, and encompasses mostly freshwater species. Few studies determined pharmaceuticals bioconcentration, and even a smaller portion combined bioconcentration with other toxicity endpoints. Results show that lipophilicity isn't a good predictor of neuroactive pharmaceuticals' bioconcentration in fish, which in turn is highly influenced by experimental parameters, including abiotic conditions, species and life-stage. The need for increased standardization of experimental settings is key towards improving accuracy of environmental risk assessments and application in future regulatory schemes. Still, increased fish lethality was linked to increased bioconcentration, yet no other correlations were observed when considering effects on growth, condition, behaviour or reproduction, likely as a result of insufficient and variable data. In the context of current environmental concentrations, several neuroactive pharmaceuticals were found to be potentially threatening, while data on occurrence is lacking for some compounds, particularly in brackish/marine systems. Specifically, nine compounds (fluoxetine, citalopram, sertraline, amitriptyline, venlafaxine, clozapine, carbamazepine, metamfetamine and oxazepam) were found at concentrations either above or critically close to minimum response concentrations, thus likely to affect fish in freshwater and brackish or marine environments, which supports further exploration in risk management strategies and monitoring programs in aquatic environments.

Proximate causes and ultimate effects of common antidepressants, fluoxetine and venlafaxine, on fish behavior

Antidepressant (AD) drugs are widely prescribed for the treatment of psychiatric disorders, including depression and anxiety disorders. The continuous use of ADs causes significant quantities of these bioactive chemicals to enter the aquatic ecosystems mainly through wastewater effluent discharge. This may result in many aquatic organisms being inadvertently affected by these drugs. Fluoxetine (FLX) and venlafaxine (VEN) are currently among the most widely detected ADs in aquatic systems. A growing body of experimental evidence demonstrates that FLX and VEN have a substantial capacity to induce neurotoxicity and cause behavioral dysfunctions in a wide range of teleost species. At the same time, these studies often report seemingly contradictory results that are confounding in nature. Hence, we clearly require comprehensive reviews that attempt to find overarching patterns and establish possible causes for these variable results. This review aims to explore the current state of knowledge regarding the neurobehavioral effects of FLX and VEN on fishes. This study also discusses the potential mechanistic linkage between the neurotoxicity of ADs and behavioral dysfunction and identifies key knowledge gaps and areas for future research.

Effects of ingestion of polyethylene microplastics on survival rate, opercular respiration rate and swimming performance of African catfish (Clarias gariepinus)

The study evaluated the impact of ingestion of microplastics on accumulation, survival, opercular respiratory rate (ORR), and swimming performance of Clarias gariepinus, the African freshwater catfish exposed to polyethylene microplastics. Juveniles were exposed for 4 days to 50-500 µm low-density polyethylene (LDPE) microplastics at four different concentrations (0.5, 1.0, 1.5, and 2.0 g/L). After 4 days of exposure, the concentration of microplastics in the gastrointestinal tract (GIT) of the fish increased with increasing concentrations of microplastics. Mean weights of microplastics in the GIT of the fish ranged from 0.0025 ± 0.001 g to 0.054 ± 0.01 g, suggesting that the fish were unable to detect and avoid ingesting the microplastics. No mortality was observed in all the treatment concentrations except in the highest concentration (2 g/L) where 10% mortality was observed. The results showed that ORR increased in a concentration and time-dependent manner. Compared with the control group, the swimming speed, travel distance and movement patterns of the fish exposed to microplastics were significantly reduced (p < 0.05). Therefore, this study helps understand the environmental impact of microplastics on C. gariepinus in freshwater environments.

Cyclophosphamide affects eye development and locomotion in zebrafish (Danio rerio)

Cyclophosphamide (CP) is a broad-spectrum anticancer drug and has been frequently detected in aquatic environments due to its incomplete removal by wastewater treatment facilities and slow degradation in waters. Its toxicity in fish remains largely unknown. In this study, zebrafish eggs <4 h post fertilization (hpf) were exposed to CP at the concentrations from 0.5 to 50.0 μg/L until 168 hpf, and its toxicity was evaluated by biochemical, transcriptomic, and behavioral approaches. The results showed that malformation and mortality rates increased with CP concentrations. The 7-day malformation EC₅₀ and mortality (LC₃₀) by CP were calculated to be 86.8 μg/L and 7.5 mg/L, respectively. Inhibited startle response (light to dark) (a minimal of 19%) and reduced swimming velocity (a minimal of 30%) were observed in the CP-exposed larvae. The thicknesses of retinal ganglion layer, inner plexiform layer, and inner nuclear layer in the retina were increased after exposure to CP. Meanwhile, exposure to CP increased karyorrhexis and karyolysis in the liver tissue. Transcriptomic analysis identified 607 differentially expressed genes (DEGs) (159 up-regulated and 448 down-regulated). A significant reduction in the transcripts of sgk1 (the FoxO pathway), jun (the MAPK pathway), and diabloa (apoptosis pathway) were observed in the CP-treated larvae. This study has demonstrated that low concentrations of CP cause malformation, reduced swimming capacity, histopathological alterations in the retina and liver tissues, and interference on transcriptional expressions of key genes associated with different pathways. The ecological risk of CP and other anticancer drugs to aquatic organisms merits future investigation.

Locomotor behavior of Neocaridina palmata: a study with leachates from UV-weathered microplastics

Weathering of plastics leads to the formation of increasingly smaller particles with the release of chemical compounds. The latter occurs with currently unknown environmental impacts. Leachate-induced effects of weathered microplastics (MPs) are therefore of increasing concern. To investigate the toxicity of the chemical mixtures from such plastics, we exposed the freshwater shrimp Neocaridina palmata to enriched leachates from unweathered and artificially weathered (UV-A/B light) MPs (≤1 mm) from recycled low-density polyethylene (LDPE-R) pellets and from a biodegradable, not fully bio-based starch blend (SB) foil. We analyzed the individual locomotor activity (moved distance and frozen events) on day 1, 3, 7 and 14 of exposure to five leachate concentrations equivalent to 0.40–15.6 g MPs L⁻¹, representing the upper scale of MPs that have been found in the environment. The median moved distance did not change as a function of concentration, except for the unweathered SB treatment on day 14 that indicated hyperactivity with increasing concentrations. Significant impacts were solely detected for few concentrations and exposure days. Generally, no consistent trend was observed across the experiments. We further assessed the baseline toxicity of the samples in the Microtox assay and detected high bioluminescence inhibitions of the bacterium Aliivibrio fischeri. This study demonstrates that neither the recycled nor the biodegradable material are without impacts on test parameters and therefore cannot be seen as safe alternative for conventional plastics regarding the toxicity. However, the observed in vitro toxicity did not result in substantial effects on the behavior of shrimps. Overall, we assume that the two endpoints examined in the atyid shrimp N. palmata were not sensitive to chemicals leaching from plastics or that effects on the in vivo level affect other toxic endpoints which were not considered in this study.

Planarian behavioural endpoints in ecotoxicology: A case study evaluating mercury and salinity effects

Freshwater planarians can be useful for the evaluation of contaminant stress on behavioral endpoints. In this work, we studied the sensitivity of the freshwater planarian Girardia tigrina in response to two model stressors (Hg and NaCl) by evaluating mortality, feeding rate and locomotion. A simple feeding assay with G. tigrina was devised, and an automated tracking system was used to evaluate locomotion. The estimated 96 h LC₅₀s were 176.8 μg L^-1 of Hg and 6.79 g L^-1 of NaCl. Acute effects of Hg also included the disintegration of tissues, and loss of pigmentation. Acute effects of NaCl included motionlessness and rupture of the tegument. Hg and NaCl sub-lethal exposures caused feeding inhibition and locomotion impairment. This study demonstrates the usefulness of planarians for ecotoxicological research and that sensitive behavioral endpoints can evaluate the sub-lethal impacts of stressors to freshwater invertebrates.

The ecological impacts of discarded cigarette butts

Cigarette butts, one of the most littered items globally, present a unique challenge to ecosystems due to their ubiquity, persistence, and potential for harm. Over 35 studies have examined the toxicity of cigarette butts in biota from aquatic and terrestrial habitats from microbes to mice, but many organisms and habitats have not been tested. Two-thirds of studies are on aquatic organisms, and lethal effects were common. Research on the impacts on terrestrial life is lagging behind. Cigarette butts can affect the growth, behaviour, and reproductive output of individual organisms in all three habitats, but research on wider effects on biodiversity and ecosystem functioning is lacking. Here, we summarise the ecotoxicological concerns and identify important knowledge gaps for future research.

The endocrine disruptor 17β-trenbolone alters the relationship between pre- and post-copulatory sexual traits in male mosquitofish (Gambusia holbrooki)

It is now well-established that reproduction in wildlife can be disrupted by anthropogenic environmental changes, such as chemical pollution. However, very little is known about how these pollutants might affect the interplay between pre- and post-copulatory mechanisms of sexual selection. Here, we investigated the impacts of 21-day exposure of male eastern mosquitofish (Gambusia holbrooki) to a field-realistic level (average measured concentration: 11 ng/L) of the endocrine-disrupting chemical 17β-trenbolone (17β-TB) on pre- and post-copulatory reproductive traits. We examined male reproductive behaviour by testing the time spent near a female behind a partition, as well as the number of copulation attempts made, and the time spent chasing a female in a free-swimming context. Sperm traits were also assayed for all males. We found that exposure of male fish to 17β-TB altered the relationship between key pre- and post-copulatory reproductive traits. Furthermore, 17β-TB-exposed males had, on average, a higher percentage of motile sperm, and performed fewer copulation attempts than unexposed males. However, there was no overall effect of 17β-TB exposure on either the time males spent associating with or chasing females. Taken together, our findings demonstrate the potential for chemical pollutants to affect both pre- and post-copulatory sexual traits, and the interplay between these mechanisms of sexual selection in contaminated wildlife.