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Open Access Publications from the University of California


The International Journal of Comparative Psychology is sponsored by the International Society for Comparative Psychology. It is a peer-reviewed open-access digital journal that publishes studies on the evolution and development of behavior in all animal species. It accepts research articles and reviews, letters and audiovisual submissions.

Volume 23, Issue 1, 2010

Special Issue

A Methodological Review of Personality-Related Studies in Fish: Focus on the Shy-Bold Axis of Behavior

Personality research has begun to take hold in the animal kingdom as psychologists turn to animal models to investigate various aspects of personality. Similarly, behavioral ecologists and related fields have begun to explore the idea that individual variation in behavior is more than just noise around an average for a given population or group of interest. As a result, many have begun to turn to personality-related questions to explain individual differences in animal behavior. Collectively, psychologists, ecologists and related fields have created a boom in animal personality-related research. This interest has expanded to a variety of fish species, with many studies focused on an important axis of behavior in humans: the shy-bold axis. Unfortunately, there has been very little consideration for the methodology employed. We review both the experimental and statistical methodology found in a body of research on fish species, for which personality-related research has been conducted. Our aim is to shed light on many important considerations that are often overlooked in order to facilitate research concerned with the reliability and validity of the many methods used.

A Y-maze Choice Task Fails to Detect Alcohol Avoidance orAlcohol Preference in Zebrafish

The zebrafish has been proposed for the analysis of the neurobiological and behavioral effects of alcohol in vertebrates. Significant behavioral changes induced by acute alcohol treatment, adaptation to chronic alcohol exposure, and withdrawal induced behavioral responses have all been shown in zebrafish. Previously, a flow-through Y-maze paradigm was proposed to directly measure alcohol preference or avoidance in zebrafish without the need to train learning-based place preference. Here, we first demonstrate that this Y-maze paradigm is capable of quantifying preference for a positive stimulus (the sight of conspecifics) and also the avoidance of a negative stimulus, a noxious olfactory cue, denatonium benzoate. Second, we test whether naïve zebrafish avoid alcohol upon first encountering this substance, and whether fish chronically exposed to alcohol show preference, or acutely alcohol treated fish show signs of intoxication leading to random choice. Our results demonstrate that acute alcohol treated fish exhibit enhanced immobility and perform at chance but chronic alcohol treated fish are not intoxicated and swim as well as naïve fish, a finding compatible with the known intoxicating effect of acute alcohol and the adaptation expected after chronic alcohol exposure. However, despite the general feasibility of the task, neither alcohol preference, nor alcohol avoidance could be detected in any of our treatment groups. We discuss the possible reasons why differential alcohol vs. freshwater choice was not found in this task and propose follow up experiments.

Zebrafish Behavior in Novel Environments:Effects of Acute Exposure to Anxiolytic Compounds and Choice of Danio rerio Line

Zebrafish (Danio rerio) associative responses are useful for pharmaceutical and toxicology screening, behavioral genetics, and discovering neural mechanisms involved in behavioral modulation. In novel environments, zebrafish swim to tank bottoms and dark backgrounds, behaviors attributed to anxiety associated with threat of predation. To examine possible genetic effects of inbreeding and segregation on this behavior, we compared Zebrafish International Resource Center (ZIRC) AB and WIK lines to zebrafish and GloFish® from a pet store (PETCO) in two qualitatively different novel environments: the dive tank and aquatic light/dark plus maze. Behavior was observed in the dive tank for 5 min, immediately followed by 5 min in the light/dark plus maze. Among strains, WIK spent more time in the dive tank top than AB (76 + 30 vs. 17 + 11 sec), and AB froze in the plusmaze center for longer than PETCO or GloFish® (162 + 61 vs. 72 + 29 or 27 + 27 sec). Further,behavior of zebrafish exposed for 3 min to 25 mg/L nicotine, desipramine, chlordiazepoxide,yohimbine, 100 mg/L citalopram, 0.05% DMSO, or 0.5% ethanol was compared to controls. Approximately 0.1% of drug is available in brain after such exposures. Desipramine or citalopram exposed fish spent more time in the dive tank top, and both reuptake inhibitors bound to serotonin transporters in zebrafish brain with high affinity (K i = 7 + 5 and 9 + 5 nM). In the plus maze, chlordiazepoxide, ethanol and DMSO-exposed fish crossed more lines and spent more time in white arms. Neither 25 mg/L nicotine nor yohimbine altered zebrafish behavior in novel environments, but nicotine was anxiolytic at higher doses. Overall, the light/dark plus maze and dive tank are distinct behavioral measures that are sensitive to treatment with anxiolytic compounds, but zebrafish line selection and solvents can influence baseline behavior in these tests.

Does Acute Alcohol Exposure Modulate Aggressive Behaviors in the Zebrafish (Danio rerio), or is the Bark Worse than the Bite?

Previous research reports that acute alcohol exposure disrupts shoaling behavior in the zebrafish. The purpose of these studies is to better understand how acute alcohol exposure (0%, 0.125%, 0.25%, 0.5%, and 1.0%) alters zebrafish behavior. The effects of alcohol on aggressive behaviors in humans have been widely researched. Previous research from this lab has shown a bimodal effect of alcohol on shoaling behavior in zebrafish, with 0.5% and 2.0% (v/v) disrupting shoaling while 1.0% and 1.5% showing no direct effect. Because shoaling is a social behavior and is altered during acute alcohol exposure, aggressive behavior between fish should be addressed. In this series of experiments we explored alcohol’s effects on aggressive behaviors. In order to address a possible role for alcohol induced aggression as it relates to shoaling we chose to examine the effects of acute alcohol exposure on zebrafish pairs. Fish were assessed during initial encounters occurring in our testing apparatus during acute alcohol exposure. Results show a change in biting as a function of all doses. Acute alcohol exposure (0.5%) also decreases overall occurrences of chasing and retreating but may increase the duration of each bout. Lastly in a separate experiment we looked at blood alcohol levels as a result of acute alcohol exposure.

The Influence of Sex and Phenotype on Shoaling Decisions in Zebrafish

Fish typically choose shoalmates with similar phenotypic characteristics to themselves, thus creating shoals for which predators have difficulty identifying and attacking one specific individual. And while shoaling should provide similar anti-predator benefits to both males and females, the two sexes do not always make the same shoaling decisions. Here we explore the effect of phenotype on sex specificshoaling in three varieties of zebrafish (Danio rerio) and the closely related pearl danio(Danio albolineatus). We hypothesized that males and females of each type of zebrafish (wildtype, golden mutants and leopard mutants), as well as male and female pearl danios, would choose to shoal rather than be alone and, when given a choice of shoalmates, would shoal with fish of their own phenotype rather than dissimilar fish. As expected, our results show that most fish preferred to shoal rather than be alone. However, while both sexes of wildtype zebrafish responded identically to shoaling decisions, male and female mutant zebrafish and pearl danio fish differed in their response to such choices. When given a choice of shoalmates, wildtype zebrafish of both sexes showed no discrimination between different D. rerio strains, although they did choose to shoal with wild type conspecifics rather than pearl danios. The shoalmate preferences of the mutant zebrafish revealed that males showed no discrimination between shoals of their own variety and wildtype shoals, while mutant females preferred shoals of their own strain. Similarly, male pearl danios showed no discrimination between shoals of their own species and shoals of wildtype zebrafish, while pearl danio females preferred their own species. These results demonstrate the complex influence of sex and phenotype on shoaling behavior.

The Behavioral and Pharmacological Actions of NMDA Receptor Antagonism are Conserved in Zebrafish Larvae

Dizocilpine maleate (MK-801) is one of several NMDA receptor antagonists that is widely used to pharmacologically model the symptoms of psychosis and schizophrenia in animals. MK-801 elicits behaviors in adult zebrafish (Danio rerio) that are phenotypically consistent with behaviors observed in humans and rodents exposed to the drug. However, the molecular and cellular processes that mediate the psychotomimetic, cognitive and locomotive behaviors of MK-801 are unclear. We exposed zebrafish larvae to MK-801 to assess their merit as a model organism to elucidate the behavioral effects of NMDA receptor blockade. Zebrafish larvae were acutely immersed in MK-801 to assess the effect on spontaneous swimming. MK-801 caused a time- and dose-dependent increase in larval swim speed, and the peak response (a five-fold increase in swim speed) was evoked by a three h exposure to a 20 uM dose. Zebrafish larvae did not exhibit sensitivity to the locomotor effectsof MK-801 until 5 dpf, suggesting a critical role for developmental in sensitivity to the drug. Exposure to the low potency NMDA antagonist, memantine, did not alter the swim speed of zebrafish larvae. Co-immersion in D 1 or D2 dopamine receptor antagonists did not disrupt the time course or magnitude of the increase in swim speed, suggesting dopaminergic signaling is not required for the locomotor actions of MK-801. Our findings of the behavioral actions of MK-801 in zebrafish larvae are consistent with previous observations in mammals and imply that the physiological, cellular and molecular processes disrupted by MK-801 are conserved in zebrafish larvae. These data suggest that the zebrafish larvae is a valid and useful model to elucidate neurobehavioral aspects of NMDA receptor antagonism and may provide insight to the neurobiology of psychosis and schizophrenia.

Genetic Analysis of the Touch Response in Zebrafish (Danio rerio)

Both mammals and zebrafish possess mechanosensory neurons that detect tactile sensation via free nerve endings. However, the basis for mechanotransduction and the unique cellular properties of these sensory neurons are poorly understood. We review the advantages of zebrafish for studies ofthe biological mechanisms involved in touch sensitivity. Importantly, Granato and colleagues (1996) demonstrated that a simple touch assay efficiently recovers mutations that affect sensory neurons.

The Developing Utility of Zebrafish in Modeling Neurobehavioral Disorders

The zebrafish (Danio rerio) is becoming increasingly popular in the field of neurobehavioral research, including experimental, genetic, and pharmacological models of human brain disorders. While zebrafish research is rapidly expanding, its application as a translational neurobehavioral model is still in its relative infancy. Therefore, further investigation of new models is needed for targeting more domains and new, more complex brain disorders. The main aim of this paper is to discuss recent developments in the field of zebrafish neurobehavioral research, and to outline important emerging topics for further studies.