Phenomics Approach to Investigate Behavioral Toxicity of Environmental or Occupational Toxicants in Adult Zebrafish (Danio rerio)

Chronic dimethomorph exposure induced behaviors abnormalities and cognitive performance alterations in adult zebrafish (Danio rerio)

Dimethomorph is a systematic fungicide that inhibits sterol synthesis in fungi and unfortunately, there was only scarce data regarding its toxicity. Therefore, considering its extensive application in agriculture and its presence in food residues and the environment, its toxicities in non-target organisms, including aquatic animals, are required to be evaluated since they are sensitive indicators of ecological change. In this study, we evaluated the toxicities of dimethomorph after chronic exposure to adult zebrafish (Danio rerio) by conducting various behavioral assays, a passive avoidance test, and biochemical assays by ELISA. From the results, ∼ 2 weeks exposure to dimethomorph caused lower locomotion, aggressiveness, and conspecific social interaction, and more robust predator avoidance behaviors. Furthermore, alterations in color preferences and short-term memory loss were also observed in the treated fish. In helping to elucidate the mechanism, the expression level of several important neurotransmitters in the brain tissue was measured. Interestingly, increment in several biomarkers, including serotonin, kisspeptin, epinephrine, norepinephrine, and dopamine was observed in the treated group along with a slight increase in other tested neurotransmitters, which were catalase, acetylcholine, and melatonin, which might play a role in the observed behavior alterations. Nevertheless, the results from the current study suggested possible alterations in the central nervous system by dimethomorph, and thus, consideration is required prior to the usage of this fungicide in the agricultural fields surrounding natural freshwater reservoirs.

A review of the neurobehavioural, physiological, and reproductive toxicity of microplastics in fishes

Microplastics (MPs) have emerged as widespread environmental pollutants, causing significant threats to aquatic ecosystems and organisms. This review examines the toxic effects of MPs on fishes, with a focus on neurobehavioural, physiological, and reproductive impacts, as well as the underlying mechanisms of toxicity. Evidence indicates that MPs induce a range of neurobehavioural abnormalities in fishes, affecting social interactions and cognitive functions. Altered neurotransmitter levels are identified as a key mechanism driving behavioural alterations following MP exposure. Physiological abnormalities in fishes exposed to MPs are also reported, including neurotoxicity, immunotoxicity, and oxidative stress. These physiological disruptions can compromise the individual health of aquatic organisms. Furthermore, reproductive abnormalities linked to MP exposure are discussed, with a particular emphasis on disruptions in endocrine signaling pathways. These disruptions can impair reproductive success in fish species, impacting population numbers. Here we explore the critical role of endocrine disruptions in mediating reproductive effects after exposure to MPs, focusing primarily on the hypothalamic-pituitary-gonadal axis. Our review highlights the urgent need for interdisciplinary research efforts aimed at elucidating the full extent of MP toxicity and its implications for aquatic ecosystems. Lastly, we identify knowledge gaps for future research, including investigations into the transgenerational impacts, if any, of MP exposure and quantifying synergetic/antagonistic effects of MPs with other environmental pollutants. This expanded knowledge regarding the potential risks of MPs to aquatic wildlife is expected to aid policymakers in developing mitigation strategies to protect aquatic species.

Epidermal oxysterols function as alarm substances in zebrafish

Alarm substances signal imminent predation thread and enable anti-predation strategies. In shoaling fish, alarm cues diffuse from injured skins that induce intense fear and anti-predation behaviors in other members. While these "fear substances" are shown to be present in numerous fishes and thought to exist in roughly 8,000 Ostariophysan species, their chemical nature remains largely unknown. We posited that fish alarm cues comprise small compounds and induce specific behaviors characteristic of fish exposed to skin extracts. Using the behaviors as bioassays, we tracked the alarm function of zebrafish skin extract to two compounds, 24-methyl-5α-cholestane-3α,7α,12α,24,28-pentahydroxy 28-sulfate, an oxysterol sulfate, and 5α-cyprinol sulfate. At concentrations of less than one nanomolar, each compound induced anti-predator behaviors and increased cortisol levels in zebrafish. Their mixture, at the natural ratio, replicated the skin extract in eliciting the full suite of anti-predator behavior patterns. Our findings reveal a molecular mechanism whereby fish escape predation danger.

A latest progress in the study of fish behavior: cross-generational effects of behavior under pollution pressure and new technologies for behavior monitoring

With the development of agriculture and industry, an increasing number of pollutants are being discharged into the aquatic environment. These pollutants can harm aquatic life. The behavioral characteristics of animals are an external manifestation of their internal mechanisms. Changes in behavior reflect damage and changes in the internal mechanisms. Environmental pollution may lead to behavioral changes not only in the parental generation but also in the offspring that has not been exposed to the pollutants. That is, the intrinsic mechanism that leads to behavioral changes is inheritable. Fish are representative species of aquatic organisms and are commonly used in various research studies. The behavior of fish has also received extensive attention, and the monitoring technology for fish behavior has developed rapidly. This article summarizes the development process of behavior monitoring technology and introduces some of the latest technologies for studying fish behavior. This article also summarizes the intergenerational effects of pollutants on fish behavior, as well as the potential intrinsic and genetic mechanisms that may lead to behavioral changes. This article provides a reference for future relevant neurobehavioral studies.

Phenomics as an approach to Comparative Developmental Physiology

The dynamic nature of developing organisms and how they function presents both opportunity and challenge to researchers, with significant advances in understanding possible by adopting innovative approaches to their empirical study. The information content of the phenotype during organismal development is arguably greater than at any other life stage, incorporating change at a broad range of temporal, spatial and functional scales and is of broad relevance to a plethora of research questions. Yet, effectively measuring organismal development, and the ontogeny of physiological regulations and functions, and their responses to the environment, remains a significant challenge. "Phenomics", a global approach to the acquisition of phenotypic data at the scale of the whole organism, is uniquely suited as an approach. In this perspective, we explore the synergies between phenomics and Comparative Developmental Physiology (CDP), a discipline of increasing relevance to understanding sensitivity to drivers of global change. We then identify how organismal development itself provides an excellent model for pushing the boundaries of phenomics, given its inherent complexity, comparably smaller size, relative to adult stages, and the applicability of embryonic development to a broad suite of research questions using a diversity of species. Collection, analysis and interpretation of whole organismal phenotypic data are the largest obstacle to capitalising on phenomics for advancing our understanding of biological systems. We suggest that phenomics within the context of developing organismal form and function could provide an effective scaffold for addressing grand challenges in CDP and phenomics.

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.

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.