A Simple Setup to Perform 3D Locomotion Tracking in Zebrafish by Using a Single Camera

Toxicity evaluation of neonicotinoids to earthworm (Eisenia fetida) behaviors by a novel locomotion tracking assay

Pesticides are substances used for controlling, preventing, and repelling pests in agriculture. Among them, neonicotinoids have become the fastest-growing class of insecticides because of their efficiency in targeting pests. They work by strongly binding to nicotinic acetylcholine receptors (nAChRs) in the central nervous system of insects, leading to receptor blockage, paralysis, and death. Despite their selectivity for insects, these substances may be hazardous to non-target creatures, including earthworms. Although earthworms may be invasive in some regions like north America, they contribute to the development of soil structure, water management, nutrient cycling, pollution remediation, and cultural services, positively impacting the environment, particularly in the soil ecosystem. Thus, this study aimed to develop a novel earthworm behavior assay since behavior is a sensitive marker for toxicity assay, and demonstrated its application in evaluating the toxicity of various neonicotinoids. Here, we exposed Eisenia fetida to 1 and 10 ppb of eight neonicotinoids (acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram pestanal, thiacloprid, thiametoxam, and sulfoxaflor) for 3 days to observe their behavior toxicities. Overall, all of the neonicotinoids decreased their locomotion, showed by a reduction of average speed by 24.94-68.63% and increment in freezing time movement ratio by 1.51-4.25 times, and altered their movement orientation and complexity, indicated by the decrement in the fractal dimension value by 24-70%. Moreover, some of the neonicotinoids, which were acetamiprid, dinotefuran, imidacloprid, nitenpyram, and sulfoxaflor, could even alter their exploratory behaviors, which was shown by the increment in the time spent in the center area value by 6.94-12.99 times. Furthermore, based on the PCA and heatmap clustering results, thiametoxam was found as the neonicotinoid that possessed the least pronounced behavior toxicity effects among the tested pesticides since these neonicotinoid-treated groups in both concentrations were grouped in the same major cluster with the control group. Finally, molecular docking was also conducted to examine neonicotinoids' possible binding mechanism to Acetylcholine Binding Protein (AChBP), which is responsible for neurotransmission. The molecular docking result confirmed that each of the neonicotinoids has a relatively high binding energy with AChBP, with the lowest binding energy was possessed by thiametoxam, which consistent with its relatively low behavior toxicities. Thus, these molecular docking results might hint at the possible mechanism behind the observed behavior alterations. To sum up, the present study demonstrated that all of the neonicotinoids altered the earthworm behaviors which might be due to their ability to bind with some specific neurotransmitters and the current findings give insights into the toxicities of neonicotinoids to the environment, especially animals in a soil ecosystem.

A comprehensive painkillers screening by assessing zebrafish behaviors after caudal fin amputation

Recently, the usage of zebrafish for pain studies has increased in the past years, especially due to its robust pain-stimulated behaviors. Fin amputation has been demonstrated to induce a noxious response in zebrafish. However, based on the prior study, although lidocaine, the most used painkiller in zebrafish, has been shown to ameliorate amputated zebrafish behaviors, it still causes some prolonged effects. Therefore, alternative painkillers are always needed to improve the treatment quality of fin-amputated zebrafish. Here, the effects of several analgesics in recovering zebrafish behaviors post-fin amputation were evaluated. From the results, five painkillers were found to have potentially beneficial effects on amputated fish behaviors. Overall, these results aligned with their binding energy level to target proteins of COX-1 and COX-2. Later, based on their sub-chronic effects on zebrafish survivability, indomethacin, and diclofenac were further studied. This combination showed a prominent effect in recovering zebrafish behaviors when administered orally or through waterborne exposure, even with lower concentrations. Next, based on the ELISA in zebrafish brain tissue, although some changes were found in the treated group, no statistical differences were observed in most of the tested biomarkers. However, since heatmap clustering showed a similar pattern between biochemical and behavior endpoints, the minor changes in each biomarker may be sufficient in changing the fish behaviors.

Short-Term Effects of Human versus Bovine Sialylated Milk Oligosaccharide Microinjection on Zebrafish Larvae Survival, Locomotor Behavior and Gene Expression

Milk oligosaccharides are a complex class of carbohydrates that act as bioactive factors in numerous defensive and physiological functions, including brain development. Early nutrition can modulate nervous system development and can lead to epigenetic imprinting. We attempted to increase the sialylated oligosaccharide content of zebrafish yolk reserves, with the aim of evaluating any short-term effects of the treatment on mortality, locomotor behavior, and gene expression. Wild-type embryos were microinjected with saline solution or solutions containing sialylated milk oligosaccharides extracted from human and bovine milk. The results suggest that burst activity and larval survival rates were unaffected by the treatments. Locomotion parameters were found to be similar during the light phase between control and treated larvae; in the dark, however, milk oligosaccharide-treated larvae showed increased test plate exploration. Thigmotaxis results did not reveal significant differences in either the light or the dark conditions. The RNA-seq analysis indicated that both treatments exert an antioxidant effect in developing fish. Moreover, sialylated human milk oligosaccharides seemed to increase the expression of genes related to cell cycle control and chromosomal replication, while bovine-derived oligosaccharides caused an increase in the expression of genes involved in synaptogenesis and neuronal signaling. These data shed some light on this poorly explored research field, showing that both human and bovine oligosaccharides support brain proliferation and maturation.

Effects of Single and Combined Ciprofloxacin and Lead Treatments on Zebrafish Behavior, Oxidative Stress, and Elements Content

Even though the toxic effects of antibiotics and heavy metals have been extensively studied in the last decades, their combined adverse impact on aquatic organisms is poorly understood. Therefore, the objective of this study was to assess the acute effects of a ciprofloxacin (Cipro) and lead (Pb) mixture on the 3D swimming behavior, acetylcholinesterase (AChE) activity, lipid peroxidation level (MDA-malondialdehyde), activity of some oxidative stress markers (SOD-superoxide dismutase and GPx-glutathione peroxidase), and the essential elements content (Cu-copper, Zn-zinc, Fe-iron, Ca-calcium, Mg-magnesium, Na-sodium and K-potassium) in the body of zebrafish (Danio rerio). For this purpose, zebrafish were exposed to environmentally relevant concentrations of Cipro, Pb, and a mixture for 96 h. The results revealed that acute exposure to Pb alone and in mixture with Cipro impaired zebrafish exploratory behavior by decreasing swimming activity and elevating freezing duration. Moreover, significant deficiencies of Ca, K, Mg, and Na contents, as well as an excess of Zn level, were observed in fish tissues after exposure to the binary mixture. Likewise, the combined treatment with Pb and Cipro inhibited the activity of AChE and increased the GPx activity and MDA level. The mixture produced more damage in all studied endpoints, while Cipro had no significant effect. The findings highlight that the simultaneous presence of antibiotics and heavy metals in the environment can pose a threat to the health of living organisms.

Machine learning based assessment of small-bodied fish tracking to evaluate spoiler baffle fish passage design

Fish passage research is important to mitigate the adverse effects of fragmented river habitats caused by waterway structures. The scale at which this research is undertaken varies from small-scale laboratory prototype studies to in-situ observations at various fish passage structures and bottlenecks. Using DeepLabCut, we introduce and evaluate a machine learning based workflow to track small-bodied fish in order to facilitate improved fish passage management. We specifically studied the behaviour and kinematics of Galaxias maculatus, a widespread diadromous Southern Hemisphere fish species. Upstream fish passage was studied in the presence of three different patches of spoiler baffles at an average water velocity of 0.4 m/s. In semi-supervised mode, the fish locations were extracted, and fish behaviour, such as swimming pathways and resting locations, was analysed based on extracted positions and recorded kinematic parameters. Individual fish behaviour and kinematic parameters were then used to assess the suitability of the three different spoiler baffle designs for enhancing fish passage. Using this technique, we were able to demonstrate where different spoiler baffle configurations resulted in significant differences in fish passage success and behaviour. For example, medium-spaced smaller baffles provided more accessible and uniform resting locations, which were required for efficient upstream passage. Results are discussed in relation to fish passage management at small instream structures.

Zebrafish: A Pharmacological Model for Learning and Memory Research

Learning and memory are essential to organism survival and are conserved across various species, especially vertebrates. Cognitive studies involving learning and memory require using appropriate model organisms to translate relevant findings to humans. Zebrafish are becoming increasingly popular as one of the animal models for neurodegenerative diseases due to their low maintenance cost, prolific nature and amenability to genetic manipulation. More importantly, zebrafish exhibit a repertoire of neurobehaviors comparable to humans. In this review, we discuss the forms of learning and memory abilities in zebrafish and the tests used to evaluate the neurobehaviors in this species. In addition, the pharmacological studies that used zebrafish as models to screen for the effects of neuroprotective and neurotoxic compounds on cognitive performance will be summarized here. Lastly, we discuss the challenges and perspectives in establishing zebrafish as a robust model for cognitive research involving learning and memory. Zebrafish are becoming an indispensable model in learning and memory research for screening neuroprotective agents against cognitive impairment.

Multiview behavior and neurotransmitter analysis of zebrafish dyskinesia induced by 6PPD and its metabolites

The typical tire manufacturing additive 6PPD, its metabolites 6PPDQ and 4-Hydroxy should be monitored because of their ubiquitous presence in the environment and the high toxicity of 6PPDQ to coho salmon. The toxic effect of 6PPD and its metabolites have been revealed superficially, especially on behavioral characteristics. However, the behavioral indicators explored so far are relatively simple and the toxic causes are poorly understood. With this in mind, our work investigated the toxic effects of 6PPD, 6PPDQ and 4-Hydroxy on adult zebrafish penetratingly through machine vision, and the meandering, body angle, top time and 3D trajectory are used for the first time to show the abnormal behaviors induced by 6PPD and its metabolites. Moreover, neurotransmitter changes in the zebrafish brain were measured to explore the causes of abnormal behavior. The results showed that high-dose treatment of 6PPD reduced the velocity by 42.4% and decreased the time at the top of the tank by 91.0%, suggesting significant activity inhibition and anxiety. In addition, γ-aminobutyric acid and acetylcholine were significantly impacted by 6PPD, while dopamine exhibited a slight variation, which can explain the bradykinesia, unbalance and anxiety of zebrafish and presented similar symptoms as Huntingdon's disease. Our study explored new abnormal behaviors of zebrafish induced by 6PPD and its metabolites in detail, and the toxic causes were revealed for the first time by studying the changes of neurotransmitters, thus providing an important reference for further studies of the biological toxicity of 6PPD and its metabolites.

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.

Copper II oxide nanoparticles (CuONPs) alter metabolic markers and swimming activity in zebra-fish (Danio rerio)

The present study aimed to compare the metabolic effects caused by using copper oxide nanoparticles with two distinct morphologies nanorods and nanosphere. The CuONPs in the form of nanorods were characterized in the order of 500 nm, on a scale of 20, 100, and 500 nm. Meanwhile, the nanosphere CuONPs were characterized in the order of 5 nm, on a 30 nm scale. The analysis of metabolic rate was performed using the closed respirometry technique, specific ammonia excretion, and swimming ability as biomarkers, the physiological effects on Danio rerio were investigated. For the experiments, 88 fish were used, exposed for 24 h at concentrations of 0, 50, 100, and 200 μg/L of copper oxide nanoparticles in the form of nanospheres and nanorods, respectively. The tests carried out with the nanorods demonstrated metabolic alterations in fish, with an increase of 294% and 321% in the metabolic rate at concentrations of 100 μg/L and 200 μg/L, respectively. Furthermore, there was a decrease in specific ammonia excretion by 34% and 83% and in swimming capacity by 34% and 55% at concentrations of 100 and 200 μg/L, respectively, when compared to the control. The tests performed with nanospheres did not show significant changes compared to the control. These experiments showed that different morphological structures of the same copper oxide nanoparticle caused different effects on fish metabolism. It is concluded that the characterization of nanoparticles is essential to understand their effects on fish, since their structural forms can cause different toxic effects on D. rerio.

Acute and Chronic Effects of Fin Amputation on Behavior Performance of Adult Zebrafish in 3D Locomotion Test Assessed with Fractal Dimension and Entropy Analyses and Their Relationship to Fin Regeneration

Simple Summary

Fin amputation is a routinely conducted procedure for various experiments, especially in zebrafish. However, no study compares the acute and chronic effects of the amputation of each fin on their behaviors. In addition, although some analgesics have been applied after the fin amputation procedure, the long-term effects of these drugs in have not been evaluated yet. In this study, we found that amputation in the caudal fin resulted in the most pronounced behavior alterations and their behavior was fully recovered before the caudal fin was fully regenerated, indicating that these behavioral changes came from pain elicited from the fin amputation. Finally, while lidocaine treatment could ameliorate the behavioral effects after the amputation procedure, it did not accelerate the behavior recovery process; instead, it caused the fish to display some slight side effects.

Abstract

The fin is known to play an important role in swimming for many adult fish, including zebrafish. Zebrafish fins consist of paired pectoral and pelvic with unpaired dorsal, anal, and caudal tail fins with specific functions in fish locomotion. However, there was no study comparing the behavior effects caused by the absence of each fin. We amputated each fin of zebrafish and evaluated their behavior performance in the 3D locomotion test using fractal dimension and entropy analyses. Afterward, the behavior recovery after the tail fin amputation was also evaluated, together with the fin regeneration process to study their relationship. Finally, we conducted a further study to confirm whether the observed behavior alterations were from pain elicited by fin amputation procedure or not by using lidocaine, a pain-relieving drug. Amputation in the caudal fin resulted in the most pronounced behavior alterations, especially in their movement complexity. Furthermore, we also found that their behavior was fully recovered before the caudal fin was fully regenerated, indicating that these behavioral changes were not majorly due to a mechanical change in tail length; instead, they may come from pain elicited from the fin amputation, since treatment with lidocaine could ameliorate the behavioral effects after the amputation procedure. However, lidocaine did not accelerate the behavior recovery process; instead, it caused the fishes to display some slight side effects. This study highlights the potential moderate severity of fin amputation in zebrafish and the importance of analgesia usage. However, side effects may occur and need to be considered since fin amputation is routinely conducted for various research, especially genomic screening.

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.

Environmental habituation and sexual composition affect juveniles' shoaling activity in a cichlid fish (Pelvicachromis taeniatus)

Group living is widespread in animals, and many fishes form shoals. Examining within-group interactions in fishes may contribute to the general understanding of dynamic social structures in animals. The sex ratio of a group has been shown to influence grouping decisions of fishes and can be expected to affect behaviour at group level. Behavioural experiments usually involve relatively short acclimatisation times, although the establishment of environmental habituation in fishes is understudied. This study tests whether the sex ratio and long-term habituation to experimental conditions influence general shoal performance (activity parameters, density) and responses of shoals to an acoustic-mechanical disturbance cue in juveniles of the cichlid fish Pelvicachromis taeniatus via individual tracking. The disturbance consisted of a defined hit against the experimental tank, which caused sudden noise and water movement. We found that a higher proportion of females increases shoal activity (swimming speed and distance covered), suggesting that female P. taeniatus are more active than males. Furthermore, shoal activity declined when shoals habituated to the experimental settings and with the time that the shoals were grouped together, which may reflect intensified group member familiarity. Moreover, behavioural changes after disturbance were weaker when individuals were kept with their group longer and more familiar to the experimental conditions. For prey species, lower activity might be beneficial under natural conditions due to lower conspicuousness of the group. We did not find any significant effects of the investigated factors on shoal density (mean interindividual distance) and speed synchronisation. The results indicate that sexual composition, familiarity between shoal members and habituation to the experimental environment affect shoal performance in a cichlid fish.

Long-Term Exposure of Alcohol Induced Behavioral Impairments and Oxidative Stress in the Brain Mitochondria and Synaptosomes of Adult Zebrafish

Alcoholism causes deleterious effects such as physiological and neuronal alterations leading to the cognitive and other behavioral impairments. Mitochondrial and synaptosomal deteriorations in the brain of alcoholic persons exhibited metabolic, biochemical changes and other related risk factors, which mainly affect the brain function. This study aimed to assess the effect of chronic alcohol-induced mitochondrial and synaptosomal oxidative damage along with behavioral impairment in adult zebrafish. Zebrafish of control group received the system water and normal diet ad libitum (group I); the other groups were treated with 0.20% alcohol (group II) and 0.40% alcohol (group III) directly in fish tank for 22 days. The result revealed significant increase in lipid peroxidation, protein carbonylation, superoxide dismutase, and glutathione, and significant decline in the activity of catalase and Na⁺/K⁺ ATPase compared to control. Furthermore, the alcohol-treated zebrafish also showed significant behavioral alterations. Collectively, this regulatory mechanism demonstrates the effect of long-term alcohol consumption in the zebrafish. Our results indicate that this recreational drug "alcohol" is harmful to brain mitochondria and synaptosomes, which are the main organelles, and play an important role in memory, learning, cognitive function, and ATP formation in the brain, which may represent a significant public health concern.

Duplicated dnmt3aa and dnmt3ab DNA Methyltransferase Genes Play Essential and Non-Overlapped Functions on Modulating Behavioral Control in Zebrafish

DNA methylation plays several roles in regulating neuronal proliferation, differentiation, and physiological functions. The major de novo methyltransferase, DNMT3, controls the DNA methylation pattern in neurons according to environmental stimulations and behavioral regulations. Previous studies demonstrated that knockout of Dnmt3 induced mouse anxiety; however, controversial results showed that activation of Dnmt3 causes anxiolytic behavior. Thus, an alternative animal model to clarify Dnmt3 on modulating behavior is crucial. Therefore, we aimed to establish a zebrafish (Danio rerio) model to clarify the function of dnmt3 on fish behavior by behavioral endpoint analyses. We evaluated the behaviors of the wild type, dnmt3aa, and dnmt3ab knockout (KO) fish by the novel tank, mirror biting, predator avoidance, social interaction, shoaling, circadian rhythm locomotor activity, color preference, and short-term memory tests. The results indicated that the dnmt3aa KO fish possessed abnormal exploratory behaviors and less fear response to the predator. On the other hand, dnmt3ab KO fish displayed less aggression, fear response to the predator, and interests to interact with their conspecifics, loosen shoaling formation, and dysregulated color preference index ranking. Furthermore, both knockout fishes showed higher locomotion activity during the night cycle, which is a sign of anxiety. However, changes in some neurotransmitter levels were observed in the mutant fishes. Lastly, whole-genome DNA methylation sequencing demonstrates a potential network of Dnmt3a proteins that is responsive to behavioral alterations. To sum up, the results suggested that the dnmt3aa KO or dnmt3ab KO fish display anxiety symptoms, which supported the idea that Dnmt3 modulates the function involved in emotional control, social interaction, and cognition.

Evaluation of the Adverse Effects of Chronic Exposure to Donepezil (An Acetylcholinesterase Inhibitor) in Adult Zebrafish by Behavioral and Biochemical Assessments

Donepezil (DPZ) is an acetylcholinesterase inhibitor used for the clinical treatment of mild cognitive impairment. However, DPZ has been reported to have adverse effects, including causing abnormal cardiac rhythm, insomnia, vomiting, and muscle cramps. However, the existence of these effects in subjects without Dementia is unknown. In this study, we use zebrafish to conduct a deeper analysis of the potential adverse effects of DPZ on the short-term memory and behaviors of normal zebrafish by performing multiple behavioral and biochemical assays. Adult zebrafish were exposed to 1 ppm and 2.5 ppm of DPZ. From the results, DPZ caused a slight improvement in the short-term memory of zebrafish and induced significant elevation in aggressiveness, while the novel tank and shoaling tests revealed anxiolytic-like behavior to be caused by DPZ. Furthermore, zebrafish circadian locomotor activity displayed a higher reduction of locomotion and abnormal movement orientation in both low- and high-dose groups, compared to the control group. Biomarker assays revealed that these alterations were associated with an elevation of oxytocin and a reduction of cortisol levels in the brain. Moreover, the significant increases in reactive oxygen species (ROS) and malondialdehyde (MDA) levels in muscle tissue suggest DPZ exposure induced muscle tissue oxidative stress and muscle weakness, which may underlie the locomotor activity impairment. In conclusion, we show, for the first time, that chronic waterborne exposure to DPZ can severely induce adverse effects on normal zebrafish in a dose-dependent manner. These unexpected adverse effects on behavioral alteration should be carefully addressed in future studies considering DPZ conducted on zebrafish or other animals.

Three- and bi-dimensional analyses of the shoaling behavior in zebrafish: Influence of modulators of anxiety-like responses

Social behaviors are key components that play adaptive roles in various species, including humans. The zebrafish (Danio rerio) is a social species and the shoaling behavior can be pharmacologically manipulated either by anxiogenic or anxiolytic substances, providing translatable data in neuropsychiatric research. Here, we aimed to characterize the shoaling behavior in zebrafish under different pharmacological manipulations in a three-dimensional (3D) perspective using the spatial coordinates of the fish positions. Temporal and spatial reconstructions of shoal occupancy were performed after exposure to conspecific alarm substance (CAS) and caffeine (CAF) (anxiogenic substances) or diazepam (DZP) (a classical anxiolytic drug). Behavioral 3D analyses and spatiotemporal reconstructions of the shoaling behavior revealed that both CAS and CAF decreased the shoal volume, the average fish distance to the centoid point, and increased shoal geotaxis, but only CAS reduced the inter-fish distance when compared to control (CTRL). Conversely, DZP group showed increased shoal volume and inter-fish distance. Because substantial differences were verified when the shoaling response was analyzed in 3D and 2D perspectives, we reinforce the use of 3D reconstructions of fish positions to assess how different manipulations affect the social behavior of zebrafish. The novel procedure described here represents an easy-to-use, inexpensive, and alternative tool to perform a spatiotemporal reconstruction of the shoal occupancy under different pharmacological manipulations, complementing the existing quantification of locomotion activity of multiple fish.

Waterborne Exposure of Paclobutrazol at Environmental Relevant Concentration Induce Locomotion Hyperactivity in Larvae and Anxiolytic Exploratory Behavior in Adult Zebrafish

The available arable land is unable to fulfill the food production need of rapidly the exponentially growing human population in the world. Pesticides are one of those different measures taken to meet this demand. As a plant growth regulator to block gibberellin, paclobutrazol (PBZ) is used excessively throughout the world to promote early fruit setting, and to increase seed setting which might be harmful because PBZ is a very stable compound; therefore, it can bioaccumulate into the food chain of an ecosystem. In the present study, we discovered unexpected effects of PBZ on zebrafish larvae and adult behaviors by challenging them with low dose exposure. Zebrafish larvae aged 4 days post-fertilization (dpf) were exposed for 24 h at 10 µg/L (0.01 ppm) and 100 µg/L (0.1 ppm) of PBZ, respectively, and adults were incubated at 100 µg/L (0.1 ppm) and 1000 µg/L (1 ppm) concentrations of PBZ, respectively, for fourteen days. After incubation, the locomotor activity, burst, and rotation movement for the larvae; and multiple behavioral tests such as novel tank exploration, mirror biting, shoaling, predator avoidance, and social interaction for adult zebrafish were evaluated. Brain tissues of the adult fish were dissected and subjected to biochemical analyses of the antioxidant response, oxidative stress, superoxide dismutase (SOD), and neurotransmitter levels. Zebrafish larvae exposed to PBZ exhibited locomotion hyperactivity with a high burst movement and swimming pattern. In adult zebrafish, PBZ resulted in anxiolytic exploratory behavior, while no significant results were found in social interaction, shoal making, and predator avoidance behaviors. Interestingly, high dose PBZ exposure significantly compromised the innate aggressive behavior of the adult fish. Biochemical assays for oxidative stress, antioxidant response, and superoxide dismutase (SOD) showed significant reductions in their relative contents. In conclusion, for the first time, our behavior assays revealed that chronic PBZ exposure induced behavioral alterations in both larvae and the adult zebrafish. Because PBZ is a widely-used plant growth regulator, we suggest that it is necessary to conduct more thorough tests for its biosafety and bioaccumulation.

Review of Copper and Copper Nanoparticle Toxicity in Fish

This review summarizes the present knowledge on the toxicity of copper and copper nanoparticles (CuNPs) to various fish species. In previous decades, the excessive usage of metal and metallic nanoparticles has increased significantly, increasing the probability of the accumulation and discharge of metals in various trophic levels of the environment. Due to these concerns, it is important to understand the toxicity mechanisms of metals and metallic nanoparticles before they lead to unhealthy effects on human health. In this review paper, we specifically focus on the effect of metal copper and CuNPs on different fish organs under different physiochemical parameters of various water bodies. Nowadays, different forms of copper have distinctive and specific usages, e.g., copper sulfate is a well-established pesticide which is used to control the growth of algae in lakes and ponds. Deactivating the fungi enzymes prevents fungal spores from germinating. This process of deactivation is achieved via the free cupric ions, which are established as the most toxic forms of copper. Complexes of copper with other ligands may or may not be bioavailable for use in aquatic organisms. On the other hand, CuNPs have shown cost-effectiveness and numerous promising uses, but the toxicity and availability of copper in a nanoparticle form is largely unknown, Additionally, physiochemical factors such as the hardness of the water, alkalinity, presence of inorganic and organic ligands, levels of pH, and temperature in various different water bodies affect the toxicity caused by copper and CuNPs. However, comprehensive knowledge and data regarding the pattern of toxicity for copper metal ions and CuNPs in marine organisms is still limited. In this review, we carry out a critical analysis of the availability of the toxicological profiles of copper metal ions and CuNPs for different fishes in order to understand the toxicity mechanisms of copper and CuNPs. We believe that this review will provide valuable information on the toxicological profile of copper, which will further help in devising safe guidelines for the usage of copper and CuNPs in a sustainable manner.

A Novel Function of the Lysophosphatidic Acid Receptor 3 (LPAR3) Gene in Zebrafish on Modulating Anxiety, Circadian Rhythm Locomotor Activity, and Short-Term Memory

Lysophosphatidic acid (LPA) is a small lysophospholipid molecule that activates multiple cellular functions through pathways with G-protein-coupled receptors. So far, six LPA receptors (LPAR1 to LPAR6) have been discovered and each one of them can connect to the downstream cell message-transmitting network. A previous study demonstrated that LPA receptors found in blood-producing stem cells can enhance erythropoietic processes through the activation of LPAR3. In the current study, newly discovered functions of LPAR3 were identified through extensive behavioral tests in lpar3 knockout (KO) zebrafish. It was found that the adult lpar3 KO zebrafish display an abnormal movement orientation and altered exploratory behavior compared to that of the control group in the three-dimensional locomotor and novel tank tests, respectively. Furthermore, consistent with those results, in the circadian rhythm locomotor activity test, the lpar3 KO zebrafish showed a lower level of angular velocity and average speed during the light cycles, indicating an hyperactivity-like behavior. In addition, the mutant fish also exhibited considerably higher locomotor activity during the dark cycle. Supporting those findings, this phenomenon was also displayed in the lpar3 KO zebrafish larvae. Furthermore, several important behavior alterations were also observed in the adult lpar3 KO fish, including a lower degree of aggression, less interest in conspecific social interaction, and looser shoal formation. However, there was no significant difference regarding the predator avoidance behavior between the mutant and the control fish. In addition, lpar3 KO zebrafish displayed memory deficiency in the passive avoidance test. These in vivo results support for the first time that the lpar3 gene plays a novel role in modulating behaviors of anxiety, aggression, social interaction, circadian rhythm locomotor activity, and memory retention in zebrafish.

Chronic Exposure to Low Concentration Lead Chloride-Induced Anxiety and Loss of Aggression and Memory in Zebrafish

Lead and lead-derived compounds have been extensively utilized in industry, and their chronic toxicity towards aquatic animals has not been thoroughly addressed at a behavioral level. In this study, we assessed the risk of exposure to lead at a waterborne environmental concentration in adult zebrafish by behavioral and biochemical analyses. Nine tests, including three-dimension (3D) locomotion, novel tank exploration, mirror biting, predator avoidance, social interaction, shoaling, circadian rhythm locomotor activity, color preference, and a short-term memory test, were performed to assess the behavior of adult zebrafish after the exposure to 50 ppb PbCl₂ for one month. The brain tissues were dissected and subjected to biochemical assays to measure the relative expression of stress biomarkers and neurotransmitters to elucidate the underlying mechanisms for behavioral alterations. The results of the behavioral tests showed that chronic exposure to lead could elevate the stress and anxiety levels characterized by elevated freezing and reduced exploratory behaviors. The chronic exposure to PbCl₂ at a low concentration also induced a sharp reduction of aggressiveness and short-term memory. However, no significant change was found in predator avoidance, social interaction, shoaling, or color preference. The biochemical assays showed elevated cortisol and reduced serotonin and melatonin levels in the brain, thus, altering the behavior of the PbCl₂-exposed zebrafish. In general, this study determined the potential ecotoxicity of long-term lead exposure in adult zebrafish through multiple behavioral assessments. The significant findings were that even at a low concentration, long-term exposure to lead could impair the memory and cause a decrease in the aggressiveness and exploratory activities of zebrafish, which may reduce their survival fitness.

Nanoplastics Cause Neurobehavioral Impairments, Reproductive and Oxidative Damages, and Biomarker Responses in Zebrafish: Throwing up Alarms of Wide Spread Health Risk of Exposure

Plastic pollution is a growing global emergency and it could serve as a geological indicator of the Anthropocene era. Microplastics are potentially more hazardous than macroplastics, as the former can permeate biological membranes. The toxicity of microplastic exposure on humans and aquatic organisms has been documented, but the toxicity and behavioral changes of nanoplastics (NPs) in mammals are scarce. In spite of their small size, nanoplastics have an enormous surface area, which bears the potential to bind even bigger amounts of toxic compounds in comparison to microplastics. Here, we used polystyrene nanoplastics (PS-NPs) (diameter size at ~70 nm) to investigate the neurobehavioral alterations, tissue distribution, accumulation, and specific health risk of nanoplastics in adult zebrafish. The results demonstrated that PS-NPs accumulated in gonads, intestine, liver, and brain with a tissue distribution pattern that was greatly dependent on the size and shape of the NPs particle. Importantly, an analysis of multiple behavior endpoints and different biochemical biomarkers evidenced that PS-NPs exposure induced disturbance of lipid and energy metabolism as well as oxidative stress and tissue accumulation. Pronounced behavior alterations in their locomotion activity, aggressiveness, shoal formation, and predator avoidance behavior were exhibited by the high concentration of the PS-NPs group, along with the dysregulated circadian rhythm locomotion activity after its chronic exposure. Moreover, several important neurotransmitter biomarkers for neurotoxicity investigation were significantly altered after one week of PS-NPs exposure and these significant changes may indicate the potential toxicity from PS-NPs exposure. In addition, after ~1-month incubation, the fluorescence spectroscopy results revealed the accumulation and distribution of PS-NPs across zebrafish tissues, especially in gonads, which would possibly further affect fish reproductive function. Overall, our results provided new evidence for the adverse consequences of PS-NPs-induced behavioral dysregulation and changes at the molecular level that eventually reduce the survival fitness of zebrafish in the ecosystem.

An Automated Assay System to Study Novel Tank Induced Anxiety

New environments are known to be anxiogenic initially for many animals including the zebrafish. In the zebrafish, a novel tank diving (NTD) assay for solitary fish has been used extensively to model anxiety and the effect of anxiolytics. However, studies can differ in the conditions used to perform this assay. Here, we report the development of an efficient, automated toolset and optimal conditions for effective use of this assay. Applying these tools, we found that two important variables in previous studies, the direction of illumination of the novel tank and the age of the subject fish, both influence endpoints commonly measured to assess anxiety. When tanks are illuminated from underneath, several parameters such as the time spent at the bottom of the tank, or the transitions to the top half of the tank become poor measures of acclimation to the novel environment. Older fish acclimate faster to the same settings. The size of the novel tank and the intensity of the illuminating light can also influence acclimation. Among the parameters measured, reduction in the frequency of erratic swimming (darting) is the most reliable indicator of anxiolysis. Open source pipeline for automated data acquisition and systematic analysis generated here and available to other researchers will improve accessibility and uniformity in measurements. They can also be directly applied to study other fish. As this assay is commonly used to model anxiety phenotype of neuropsychiatric ailments in zebrafish, we expect our tools will further aid comparative and meta-analyses.

The zebrafish subcortical social brain as a model for studying social behavior disorders

Social behaviors are essential for the survival and reproduction of social species. Many, if not most, neuropsychiatric disorders in humans are either associated with underlying social deficits or are accompanied by social dysfunctions. Traditionally, rodent models have been used to model these behavioral impairments. However, rodent assays are often difficult to scale up and adapt to high-throughput formats, which severely limits their use for systems-level science. In recent years, an increasing number of studies have used zebrafish (Danio rerio) as a model system to study social behavior. These studies have demonstrated clear potential in overcoming some of the limitations of rodent models. In this Review, we explore the evolutionary conservation of a subcortical social brain between teleosts and mammals as the biological basis for using zebrafish to model human social behavior disorders, while summarizing relevant experimental tools and assays. We then discuss the recent advances gleaned from zebrafish social behavior assays, the applications of these assays to studying related disorders, and the opportunities and challenges that lie ahead.

Overexpression of Notch Signaling Induces Hyperosteogeny in Zebrafish

Notch signaling is one of the evolutionarily conserved signaling pathways in multicellular organisms. It plays an important role in embryonic development. During skeletal development of vertebrates, it regulates bone homeostasis by manipulating both osteoblastogenesis and osteoclastogenesis through different mechanisms. However, due to the different nature of Notch signaling in mesenchymal stem cell and osteoblast, regulation of Notch signaling in bone-related diseases remains unsettled. Previous studies by cell culture and mouse models showed contradictory results regarding the role of Notch signaling in bone homeostasis. To clarify the role of Notch signaling in osteogenesis, we established a zebrafish model, in which Notch1a intracellular domain (N1aICD) was specifically expressed in the osteoblasts. We found that overexpression of N1aICD in osteoblasts caused hyperosteogeny in the column region of zebrafish with the morphology of narrowed neural/hemal canals. Moreover, increased metabolic activity of osteoblasts instead of augmenting osteoblast number led to hyperosteogeny in N1aICD-overexpressed zebrafish. In summary, we successfully established a transgenic zebrafish line overexpressing N1aICD to clarify the in-vivo function of Notch signaling during osteoblastogenesis. In the future, this fish line can serve as a valuable tool to test the therapeutic drugs for hyperosteogeny.

Establishing simple image-based methods and a cost-effective instrument for toxicity assessment on circadian rhythm dysregulation in fish

Analysis of circadian rhythm behavior alteration in fish for toxicity assessment usually requires expensive commercial equipment and laborious and complicated tweaking. Here, we report a simple setup that consists of a custom-made light box equipped with white and 940 nm light-emitting diode (LED) light strips as light sources, where the locomotion activities of zebrafish or catfish are captured using an infrared-sensitive coupled charged device (CCD). The whole setup was housed in a temperature-controlled incubator to isolate external noise and to maintain consistent experimental conditions. The video recording and light triggering were synchronized using Total Recorder, a recording scheduling software. By using the setup mentioned above and open source software such as ImageJ or idTracker, the locomotion activities of diurnal (e.g. zebrafish) and nocturnal (e.g. catfish) fish during day and night cycles can be quantitatively analyzed. We used simple image-based methods and a cost-effective instrument to assess the circadian rhythm of multiple fish species, as well as other parameters such as age, ambient temperature and chemical toxicology with high precision and reproducibility. In conclusion, the instrument setting and analysis methods established in this study provide a reliable and easy entry point for toxicity assessment on circadian rhythm dysregulation in fish.

Summary: A cost-effective device and two methods to measure the circadian rhythm in diurnal and nocturnal fish, providing a reliable entry point for toxicity assessment on circadian rhythm dysregulation in fish.

Zebrafish Mutants Carrying Leptin a (lepa) Gene Deficiency Display Obesity, Anxiety, Less Aggression and Fear, and Circadian Rhythm and Color Preference Dysregulation

Leptin, a hormone secreted by peripheral adipose tissues, regulates the appetite in animals. Recently, evidence has shown that leptin also plays roles in behavioral response in addition to controlling appetite. In this study, we examined the potential function of leptin on non-appetite behaviors in zebrafish model. By using genome editing tool of Transcription activator-like effector nuclease (TALEN), we successfully knocked out leptin a (lepa) gene by deleting 4 bp within coding region to create a premature-translation stop. Morphological and appetite analysis showed the lepa KO fish display a phenotype with obese, good appetite and elevation of Agouti-related peptide (AgRP) and Ghrelin hormones, consistent with the canonical function of leptin in controlling food intake. By multiple behavior endpoint analyses, including novel tank, mirror biting, predator avoidance, social interaction, shoaling, circadian rhythm, and color preference assay, we found the lepa KO fish display an anxiogenic phenotype showing hyperactivity with rapid swimming, less freezing time, less fear to predator, loose shoaling area forming, and circadian rhythm and color preference dysregulations. Using biochemical assays, melatonin, norepinephrine, acetylcholine and serotonin levels in the brain were found to be significantly reduced in lepa KO fish, while the levels of dopamine, glycine and cortisol in the brain were significantly elevated. In addition, the brain ROS level was elevated, and the anti-oxidative enzyme catalase level was reduced. Taken together, by performing loss-of-function multiple behavior endpoint testing and biochemical analysis, we provide strong evidence for a critical role of lepa gene in modulating anxiety, aggression, fear, and circadian rhythm behaviors in zebrafish for the first time.

Evaluation of the Effects of Carbon 60 Nanoparticle Exposure to Adult Zebrafish: A Behavioral and Biochemical Approach to Elucidate the Mechanism of Toxicity

There is a growing concern for the potential toxicity of engineered nanomaterials that have made their way into virtually all novel applications in the electronics, healthcare, cosmetics, technology, and engineering industries, and in particular, biomedical products. However, the potential toxicity of carbon 60 (C₆₀) at the behavioral level has not been properly evaluated. In this study, we used idTracker, a multitracking algorithm to quantitatively assess behavioral toxicity induced by C₆₀ nanoparticles (C₆₀ NPs) in adult zebrafish. We demonstrated that locomotion, novel tank exploration, aggression, shoaling, and color preference activities of the C₆₀ NPs-treated fish was significantly reduced. In addition, the C₆₀ NPs-treated fish also displayed dysregulation of the circadian rhythm by showing lower locomotion activities in both day and night cycles. The biochemical results showed that C₆₀ NPs exposure at low concentration induced oxidative stress and DNA damage, reduced anti-oxidative capacity and ATP (adenosine triphosphate) levels, and induced stress-associated hormones, hypoxia, as well as inflammation marker upregulation in muscle and gill tissues. Together, this work, for the first time, provide direct evidence showing that the chronic exposure of C₆₀ NPs induced multiple behavioral abnormalities in adult zebrafish. Our findings suggest that the ecotoxicity of C₆₀ NPs towards aquatic vertebrates should be carefully evaluated.

A Versatile Setup for Measuring Multiple Behavior Endpoints in Zebrafish

The measurement of multiple behavior endpoints in zebrafish can provide informative clues within neurobehavioral field. However, multiple behavior evaluations usually require complicated and costly instrumental settings. Here, we reported a versatile setting that applied ten acrylic tanks arranging into five vertical layers and two horizontal columns to perform multiple behavior assays simultaneously, such as the novel tank diving test, mirror-biting test, social interaction, shoaling, and predator escape assay. In total, ten behavioral performance were collected in a single video, and the XY coordination of fish locomotion can be tracked by using open source software of idTracker and ImageJ. We validated our setting by examining zebrafish behavioral changes after exposure to low dose ethanol (EtOH) for 96 h. Fish were observed staying longer time at bottom of the tank, less mirror biting interest, higher freezing time, less fear in predator test, and tight shoaling behaviors which indicated the anxiogenic effect was induced by low dosage exposure of EtOH in zebrafish. In conclusion, the setting in this study provided a simple, versatile and cost-effective way to assess multiple behavioral endpoints in zebrafish with high reliability and reproducibility for the first time.

Zinc Chloride Exposure Inhibits Brain Acetylcholine Levels, Produces Neurotoxic Signatures, and Diminishes Memory and Motor Activities in Adult Zebrafish

In this study, we evaluated the acute (24, 48, 72, and 96 h) and chronic (21 days) adverse effects induced by low doses (0.1, 0.5, 1, and 1.5 mg/L) of zinc chloride (ZnCl₂) exposure in adult zebrafish by using behavioral endpoints like three-dimensional (3D) locomotion, passive avoidance, aggression, circadian rhythm, and predator avoidance tests. Also, brain tissues were dissected and subjected to analysis of multiple parameters related to oxidative stress, antioxidant responses, superoxide dismutase (SOD), neurotoxicity, and neurotransmitters. The results showed that ZnCl₂-exposed fishes displayed decreased locomotor behavior and impaired short-term memory, which caused an Alzheimer’s Disease (AD)-like syndrome. In addition, low concentrations of ZnCl₂ induced amyloid beta (amyloid β) and phosphorylated Tau (p-Tau) protein levels in brains. In addition, significant induction in oxidative stress indices (reactive oxygen species (ROS) and malondialdehyde (MDA)), reduction in antioxidant defense system (glutathione (GSH), GSH peroxidase (GSH-Px) and SOD) and changes in neurotransmitters were observed at low concentrations of ZnCl₂. Neurotoxic effects of ZnCl₂ were observed with significant inhibition of acetylcholine (ACh) activity when the exposure dose was higher than 1 ppm. Furthermore, we found that zinc, metallothionein (MT), and cortisol levels in brain were elevated compared to the control group. A significantly negative correlation was observed between memory and acetylcholinesterase (AChE) activity. In summary, these findings revealed that exposure to ZnCl₂ affected the behavior profile of zebrafish, and induced neurotoxicity which may be associated with damaged brain areas related to memory. Moreover, our ZnCl₂-induced zebrafish model may have potential for AD-associated research in the future.

The Tagging Procedure of Visible Implant Elastomers Influences Zebrafish Individual and Social Behavior

One commonly used method to preserve individual identity in the study of social behavior of zebrafish is through silicone-based visible implant elastomers (VIEs), which represent a safe and durable tagging procedure. While the effects of VIE tagging on welfare and general health have been addressed in detail, whether this procedure influences social behavior remains unclear. In this study, we compared individual and group behaviors exhibited by shoals composed of three individuals: two nontagged and one (focal subject) that was either nontagged (control condition) or sham-, purple-, blue-, or yellow tagged. Traditional behavioral parameters of activity, shoaling, and schooling (speed, polarization, and interindividual distances), along with an information-theoretic measure of social interaction (transfer entropy), were used to study the effect of tagging. Our findings indicate that tagging procedure per se significantly increased individual speed of the tagged subjects and of the group. The tagging procedure also altered the level of interaction between individuals, measured by transfer entropy. Conversely, tagging procedure did not influence shoaling and schooling tendencies. These findings suggest that VIE tagging may elicit some level of stress, which may affect some behavioral responses more than others. We recommend use of alternative methods such as multitracking systems when possible.