Janette Lebron’s scientific contributions

Shoals of fish are often composed of individuals similar in body size or other characteristics. This study tested for the assortment by sex (controlled for body size) in a species with a low degree of sexual dimorphism. Zebrafish (Danio rerio) shoaling was studied in the laboratory using four different experiments utilizing two different methodologies. In most of the experiments, females showed a statistically significant preference for shoaling with other females, but males typically showed no preference. In choice experiments zebrafish preferred swimming near a compartment containing another zebrafish compared to swimming near an empty compartment, but this preference was strongest for same-sex pairings, both female-female and male-male. In additional choice experiments, the results showed a preference among females (but not males) for a group of three same-sex fish over three opposite-sex fish. There was no consistent result when females were forced to choose between three females and six males, thus the preference for same-sex shoalmates may be balanced with a preference for larger shoals. The second methodology used freely-swimming groups of four fish. Females swam closer to females than to males, but males showed no preference. Few previous studies have demonstrated sex-assortative shoaling.