The effects of exploratory behavior on physical activity in a common animal model of human disease, zebrafish (Danio rerio)

Zebrafish (Danio rerio) are widely accepted as a multidisciplinary
vertebrate model for neurobehavioral and clinical studies, and more
recently have become established as a model for exercise physiology and
behavior. Individual differences in activity level (e.g., exploration)
have been characterized in zebrafish, however, how different levels of
exploration correspond to differences in motivation to engage in swimming
behavior has not yet been explored. We screened individual zebrafish in
two tests of exploration: the open field and novel tank diving tests. The
fish were then exposed to a tank in which they could choose to enter a
compartment with a flow of water (as a means of testing voluntary
motivation to exercise). After a 2-day habituation period, behavioral
observations were conducted. We used correlative analyses to investigate
the robustness of the different exploration tests. Due to the complexity
of dependent behavioral variables, we used machine learning to determine
the personality variables that were best at predicting swimming behavior.
Our results show that contrary to our predictions, the correlation between
novel tank diving test variables and open field test variables was
relatively weak. Novel tank diving variables were more correlated with
themselves than open field variables were to each other. Males exhibited
stronger relationships between behavioral variables than did females. In
terms of swimming behavior, fish that spent more time in the swimming zone
spent more time actively swimming, however, swimming behavior was
inconsistent across the time of the study. All relationships between
swimming variables and exploration tests were relatively weak, though
novel tank diving test variables had stronger correlations. Machine
learning showed that three novel tank diving variables (entries
top/bottom, movement rate, average top entry duration) and one open field
variable (proportion of time spent frozen) were the best predictors of
swimming behavior, demonstrating that the novel tank diving test is a
powerful tool to investigate exploration. Increased knowledge about how
individual differences in exploration may play a role in swimming behavior
in zebrafish is fundamental to their utility as a model of exercise
physiology and behavior.