Novelty seeking behaviors in zebrafish (Danio rerio) in a novel tank test. Novelty seeking behaviors were measured by a novel tank test in zebrafish. Zebrafish were divided into two groups, short-term-isolated (1 day), and long-term-isolated (4 weeks). There was no significant difference in horizontal activity between two groups; however, the isolated groups showed more vertical activity compared with the group-reared control. The results suggested that long-term-isolated zebrafish, had higher activity levels compared to the short-term-isolated, or group-reared zebrafish. Thus, isolation and social isolation cause behavioral alteration of zebrafish. These data also indicate that fish can be used as a new model in the field of psychopharmacology.