A Method for Sorting Zebrafish on the Exploratory-Boldness Behavioral Axis

A major axis of inter-individual behavioral variation is correlated behavioral traits, known variously as behavioral syndromes, personality, or temperament. The zebrafish is a good model organism with which to explore the molecular genetic mechanisms of personality. The first step in the study of behavioral syndromes is development of reliable assays for sorting fish along an axis of behavioral variation. Here, we describe an assay for measuring exploratory tendency, which is linked to boldness in the face of predation threat, thus forming a exploratory-boldness behavioral syndrome. Ten fish were placed in the first of a series of five chambers connected by narrow-diameter lengths of PVC tubing, presenting, in essence, a serial open-field test for tendency to explore novel areas. Some individuals passed through the tunnels to explore the next chamber while some individuals were reluctant to do so. After 7 days, individuals in the last two chambers were designated as exploratory, while individuals that remained in the first two chambers were designated as nonexploratory. These fish were then transferred individually to a predator-inspection apparatus containing a large adult convict cichlid (potential predator) behind a mesh partition. Exploratory zebrafish moved less and spent more time near the predator than nonexploratory individuals did. Thus, the multi-chamber exploration open-field test was a useful assay for scoring zebrafish along an exploratory-boldness behavioral syndrome. The serial open-field test has been modified to sort 2-week-old larvae, which opens the door to mass-screening of mutagen-treated embryos.