Long‐term repeatability of behaviours in zebrafish ( Danio rerio )

Sex, drugs, and zebrafish: Acute exposure to anxiety-modulating compounds in a modified novel tank dive test

This study investigated the effects of anxiogenic and anxiolytic drugs on zebrafish (Danio rerio) behaviour using a modified novel tank dive test with higher walls and a narrower depth. Zebrafish were administered chondroitin sulfate, beta-carboline, Delta-9-tetrahydrocannabinol (THC), ethanol, and beta-caryophyllene, and their behaviours were evaluated for geotaxis, swimming velocity, and immobility. Both anxiogenic and anxiolytic compounds generally increased bottom-dwelling behaviour, suggesting that the tank's modified dimensions significantly influence zebrafish responses. EC50 values for ethanol showed a lower threshold for velocity reduction compared to zone preference. Chondroitin sulfate uniquely caused a sex-specific increase in male swimming velocity, whereas no other sex-differences were observed with any compound. Interestingly, the presence of drug-treated fish did not alter the behaviour of observer fish, suggesting limited social buffering effects. The findings underscore the complexity of zebrafish behavioural phenotypes and highlight the need for considering tank dimensions and multiple behavioural parameters to accurately assess the effects of anxiety-modulating drugs. This study demonstrates the utility of the modified novel tank dive test in providing nuanced insights into the behavioural effects of different pharmacological agents in zebrafish.

Relationship between boldness and exploratory behavior in adult zebrafish

Behavioral responses vary between individuals and may be repeated in different contexts over time. When a behavioral response set is linked and present regardless of the context, it characterizes a behavioral syndrome. By evaluating how bold and shy (profiles related to risk-taking) individuals perform about exploration and anxiety, we can predict relationships of behavioral syndromes and better understand how different axis of personality is formed. Here we classified the profiles by risk-taking and evaluated their exploration behavior in the open field test. In this context, the two groups showed significant differences in thigmotaxis behavior: bold individuals habituate faster and show decreased thigmotaxis (less anxiety), while shy ones are less prone to leave the security of the side areas of the open tank and present higher anxiety. We emphasized the importance of further investigating the behavior of these profiles in other contexts and the importance of each one for the evolution and fitness of the species, in addition to a better understanding of which behaviors are involved in the behavioral syndromes in zebrafish.

The zebrafish Multivariate Concentric Square Field: A Standardized Test for Behavioral Profiling of Zebrafish (Danio rerio)

The zebrafish (Danio rerio) is an important model organism in the study of the neurobiological basis of human mental disorders. Yet the utility of this species is limited by the quality of the phenotypical characterization tools available. Here, we present a complex testing environment for the quantification of explorative behavior in adult zebrafish, the zebrafish Multivariate Concentric Square Field™ (zMCSF), adapted from the rodent equivalent that has been used in > 40 studies. The apparatus consists of a central open area which is surrounded by a dark corner with a roof (DCR), corridors, and an inclined ramp. These areas differ in illumination, water depth, and are sheltered or exposed to different degrees. We quantified behavior of male and female wild-caught and AB strain zebrafish in the zMCSF (day 1) and cross-validated these results using the novel tank diving test (NTDT) (day 2). To assess the effect of repeated testing, AB zebrafish we tested a second time in both tests 1 week later (on days 7 and 8). We detected strong differences between the strains, with wild zebrafish swimming faster and spending more time in the corridors and on the ramp, while they avoided the open area in the center. AB zebrafish were less hesitant to enter the center but avoided the ramp, and often left one or more zones unexplored. No major sex differences in exploratory behavior were detected in either strain, except for a slightly higher velocity of AB males which has been reported before. Importantly, the zMCSF was largely resilient to repeated testing. The diving test revealed only one difference confined to one sex; wild females paid more visits to the top third than AB females. In isolation, this finding could lead to the conclusion that wild zebrafish are more risk-taking, which is incorrect given this strain’s avoidance of open areas. To conclude, our results suggest that the zMCSF presents a sophisticated behavioral tool that can distinguish between different magnitudes and types of risk, allowing the user to create an intricate behavioral profile of individual adult zebrafish.

Sex and Population Drive Interindividual Variations in a Cognitive Task Across Three Populations of Wild Zebrafish

Animal personality refers to the consistency of variation in behavior among individuals which may be the driving force behind variations in complex behaviors as well. Individual personality could predict how well an organism would perform in behavior and cognition related tasks, as well as survive and thrive in its environment. Therefore, we would expect inter-individual variations in many behaviors, which would persist even if habituation to the experimental setup occurs, which generally results in convergence of behavior (i.e., the difference between individuals becomes less pronounced). Our study used wild-caught zebrafish (Danio rerio) from three natural habitats with differing ecological regimes, to understand how consistency and repeatability in specific traits such as boldness, exploration, and spatial ability varies across and within populations even when habituation causes change in behavior. We found that the extent of individual variation differs between populations, with dynamic habitats showing similar repeatability. This indicates that habitat conditions are important drivers of individual variation in addition to other factors, such as sex or size of individuals within populations. Although we found that sex and size played an important role within some populations for some behaviors, in others, the variation was likely caused by other factors (for example, ecological factors such as vegetation and/or resource availability), for which we have not accounted. This study underlines the importance of studying inter-individual differences as the phenomenon that underpins multiple behavioral traits and explains the possible role of environmental and inherent factors that drive these differences.

An efficient new assay for measuring zebrafish anxiety: Tall tanks that better characterize between-individual differences

BACKGROUND

Zebrafish (Danio rerio) are increasingly being used to model anxiety. A common behavioral assay employed for assessing anxiety-like behaviors in zebrafish is the "novel tank test". We hypothesized that using deeper tanks in this test would result in greater between-individual variation in behavioral responses and a more 'repeatable' assay.

NEW METHODS

After mapping the literature and identifying common behavioral parameters used in analysis, we performed novel tank anxiety tests in both custom-designed 'tall' tanks with increased depth and 'short' trapezoidal tanks. We compared the repeatability of the behavioral parameters between tall and short tanks and also investigated sex differences.

RESULTS

Overall, regardless of tank depth, almost all behavioral parameters associated with anxiety in zebrafish were significantly repeatable (R = 0.24 to 0.60). Importantly, our tall tanks better captured between-individual differences, resulting in higher repeatability estimates (average repeatability tall tanks: R = 0.46; average repeatability short tanks: R = 0.36) and clearer sex differences.

CONCLUSIONS

Our assay using tall tanks has advantages over tests based on short tanks which underestimate repeatability. We argue that use of deeper tanks will improve the reliability of behavioral data across studies using novel tank tests for zebrafish. Our results also call for increased attention in designing the most appropriate assay in biomedical and behavioral sciences as current methods may lack the sensitivity to detect subtle, yet important, information, such as between-individual variation, an important component in assessing the reliability of behavioral data.

Vision of conspecifics decreases the effectiveness of ethanol on zebrafish behaviour

Aquatic organisms in pharmacology and toxicology research are often exposed to compounds in isolation prior to physiological or behavioural testing. Recent evidence suggests that the presence of conspecifics during a stressful event can modulate behavioural outcomes (called 'social buffering') when testing occurs within the same context. It is unknown, however, whether the social environment during exposure interacts with the efficacy of anxiety-altering substances when subsequently tested in the absence of conspecifics. In this study, zebrafish were individually exposed to habitat water or ethanol (1.0% vol/vol) while untreated conspecifics were visually present or absent during dosing. Using the novel object approach test, a validated test of boldness and anxiety-like behaviour, we observed significantly greater effects of ethanol in isolated fish, compared to fish with a view of conspecifics during dosing. These results were not explained by altered locomotion during exposure, which might otherwise increase drug uptake. This highlights the need to consider the social environment during exposure when conducting and interpreting behavioural research involving drug or toxicant exposure.