Aggregation in groups provides many animals with the ecological benefits of protection from predators, increased access to food, and greater opportunity for mating. Countless studies on the shoaling (aggregation) behavior of fishes have demonstrated various influences on how individuals choose which shoal to join. These include environmental factors such as predation pressure, food availability, and habitat variation, as well as attributes of the shoal that the individual may join, such as shoal size, body color/size of shoalmates, and sex ratios. With the surge in studies on behavioral syndromes (consistent individual behaviors) and their possible influences on behavioral decisions, we sought to determine if the innate personality of an individual fish would influence shoalmate choices that could potentially effect the ecological benefits associated with group behavior. We quantified the aggressive/bold or submissive/shy personalities of individual male and female zebrafish and then the shoalmate preferences of individual fish were tested in dichotomous shoal choice assays. Variations in shoal size and sex composition of the shoal represented different levels of ecological benefits. We hypothesized that fish, regardless of personality, would benefit most from and therefore should choose larger shoals and shoals of fish of the opposite sex.
Results/Conclusions
Both sexes of fish made shoaling choices consistent with the hypothesis that shoaling is beneficial and spent significantly more time near shoals of fish rather than be alone. Contrary to our predictions, when given the choice between a small or large shoal, neither males nor females associated significantly more with the larger shoals. When given the choice between same-sex and opposite-sex shoals, both males and females spent more time with shoals of female fish, rather than shoals of male fish. In terms of consistent behavioral syndromes, males were much more consistent in their behaviors and females exhibited much more individual variability across multiple contexts. The aggressive individual behavioral types appear to influence shoal choices, at least for males, with more aggressive males generally being more likely to choose shoals of males rather than females and being more likely to swim alone than to choose to swim with a shoal. These sex differences in the expression of behavioral syndromes and their influences on choices related to grouping have serious implications for the behavioral ecology and evolution of social animals.