Individual variations in behavior and free cortisol responses to acute stress in tiger pufferfish Takifugu rubripes

The aim of the present study was for individual variation in behavior to be characterized and related to differences in physiological stress responses in juvenile tiger pufferfish (fugu) Takifugu rubripes. A set of siblings (n = 330) from wild parents was subjected to behavior tests, and some were classified into active and inactive groups (n = 42 each group). The active animals consisted of those individuals that kept active swimming during 6 min after transfer from one tank to another, and the inactive animals were those that stopped swimming within 6 min. Time-course acute stress responses, which were elicited by anesthesia and subsequent removal of a pectoral fin, were compared between the active and inactive fish. The stress indicators used were free and total plasma cortisol, and plasma glucose. Although no significant difference was observed at each sampling point between groups, the inactive fish required shorter recovery time from acute stress in all three indicators than the active fish. The percentage of free to total plasma cortisol in the pre-stress condition was significantly lower in the inactive group than in the active group. Our findings indicate that fugu has behavioral variation that is associated with stress responsiveness. The inactive fish are expected to be more tolerant of stress and suitable for aquaculture.