Factors Affecting the Fear Response of Hatchery-Reared Tiger Puffer Takifugu Rubripes Juveniles

Tiger puffer Takifugu rubripes is a commercially important fish in Japan. Due to the decline of natural stocks, stock enhancement programs are performed in many prefectures in Japan. There are feasible cases for stock enhancement when hatchery-reared juveniles were released at large size (> ca. 7 cm in standard length; SL), however, releasing small-juveniles (< ca. 5 cm) has resulted in unsatisfactory outcomes. Hatchery-reared juveniles in small body size are inferior in fear response (settlement behavior at the new environment).  Therefore, we investigated the factors affecting fear response of hatchery-reared tiger puffer juveniles.  We observed settlement behavior of juveniles (5.5±0.3 cm, 10.9±0.7 cm SL) for 6 hours after transfer into different salinities (15, 32 psu) of static or spring-water conditions with sand-covered tank. Settlement rate of small juveniles (5.5±0.3 cm SL) was lower (P<0.0001) than large juveniles (10.9±0.7 cm SL). Spring-water (P<0.01) and 15 psu (P<0.05) stimulated settlement. Administration of tetrodotoxin (TTX) to the juvenile puffer significantly improved fear response and decreased agonistic interactions, and raised the survival after release to the environment with predators.