Does personality type predict exercise behavior in zebrafish, Danio rerio, a common animal model of human diseases.

Introduction: Although it is clear how a person’s physical health (e.g. blood pressure and muscle mass) will contribute to activity level, how the brain (in particular, personality) influences physical activity is an area that has been understudied. Personality refers to consistent, long-term behavioral, emotional, and physiological differences in suites of traits (e.g. bold-shy spectrum, aggression, exploration) among individuals of the same species (Carere and Locurto, 2011). How our personality can motivate us to pursue physical activity is something that we really need to study in order to understand our mental health, promote improvement in health and stress management and also find a way to motivate non-active people to exercise based on their personality. We use animal models, in particular mice and rats, to fill in gaps in our knowledge where studies on humans are lacking. Using rodents is much simpler and eliminates societal, gender, age, diet, and other environmental and genetic effects, therefore allowing researchers to study the connection between personality and physical activity more clearly (Garland et al. 2011). Most rodent studies of exercise and behavior utilize voluntary wheel-running, which is rewarding for rodents and represents self-motivating behavior. Although much research has been conducted on personality traits in rodents (see review by Gosling, 2001), there is limited research on how personality traits affect physical activity. Where the interaction of personality and exercise has been explored, results have been contradictory; high levels of exploration in the open field test have been associated with increased (McQuaid et al. 2012), decreased (Garrett et al. 2012) and no change (Pietropaolo et al. 2006) in wheel running mice. Zebrafish (Danio rerio) are a well-known animal model of human disease (e.g. cancer, Alzheimer's disease), but only recently has their potential as a model for exercise physiology and behavior come to light (Luchiari and Chacon, 2013; Gilbert et al. 2014). Zebrafish represent a superior alternative for studying the interaction between personality and physical activity because they are cheap and easy to maintain, they possess many homologous genes to humans, and many of their neuro-anatomical pathways resemble that of the mammalian brain. Moreover, a number of studies have already documented the occurrence of personality traits in zebrafish, and there are a number of standard assays for measuring these (Yuan et al. 2018). However, despite these advantages and advances in our knowledge, the effects of personality traits on physical activity have not yet been explored in zebrafish. This project aims to enhance our understanding of the connection between personality and physical activity. Thus, the overarching objective of this project is to understand how personality traits influence physical activity using a common animal model of human disease, the zebrafish. Materials and Method: The experiment was conducted using 48 mature wildtype zebrafish that were be purchased from the College of Medicine, Hershey, and were being given 7 days to acclimatize. Groups of zebrafish (n = 6 per tank, 8 tanks, equal numbers of male and female) were housed in standard laboratory conditions. Individual fish were screened for personality traits using two different behavioral tests; the open field test (looks at exploration/boldness) and the novel tank diving test (measures anxiety and overall activity levels). In the open field test, the fish was allowed to explore an open arena and was recorded for 5 minutes. The open-field test consisted of a plain tank surrounded by black plastic on three sides to eliminate the influence of the surrounding environment. How much time the fish spent close to the walls (thigmotaxic behavior) or exploring the middle of the arena was indicative of how exploratory/bold it was. The fish was then placed in the novel tank diving test and the vertical exploratory behavior was taken into account; how long the fish took to emerge to the top of the tank after initially diving to the bottom was indicative of anxiety level. Once all individuals were screened for personality traits, each individual was put in a large tank with 3 compartments: an exercise zone (water flow set to 0.5 m/s), a sedentary zone (no flow), and a neutral middle zone where food was delivered. The fish were given free access to each zone through small doors in the dividers. After a two-day acclimatization period, the fish were recorded for an hour in the morning and evening for 2 days. The videos were analyzed to determine how much time the fish spent in the exercise zone versus the sedentary zone using the Behavioral Observation Research Interactive Software (BORIS). An acetate grid was used to evaluate zebrafish swimming activity such as thigmotaxic or exploratory behaviors. Variables analyzed included: latency to enter the top, movement rate, time spent frozen/ proportion of time spent frozen; the proportion of time in the middle.