Reiji Masuda and David A. Ziemann

The Oceanic Institute, 41-202 Kalanianaole Hwy., 
Waimanalo, HI 96795 USA

Aquarium Sciences and Conservation , in press

Understanding behavioral characteristics of target species is essential to improve the aquaculture technique and conservation strategy. With this concept we studied behavioral characteristics of Pacific threadfin, Polydactylus sexfilis, (Valenciennes) juveniles. First, the ontogeny of schooling behavior was observed in hatchery tanks reared with different dietary conditions. Pacific threadfin formed schools from day 19 if the proper amount of docosahexaenoic acid (DHA) was provided in their diet. A second experiment was to evaluate ontogenetic changes of learning capability and stress recovery in this species. Juveniles at 50 mm and 90 mm in FL were better in their learning capability compared to smaller (22 mm, 36 mm) or larger (130 mm) groups. Stress recovery was quicker in larger fish at 90 mm and 130 mm. The third study was to estimate the ontogenetic changes of predator avoidance against bluefin trevally. Juveniles at 70 mm and 100 mm were eaten easily, whereas juveniles at 140 mm and 190 mm survived steadily. In the fourth experiment we compared behavioral rhythm between the wild-collected and the cultured juveniles. Both wild and cultured fish swam faster at night than in the daytime. Wild fish lost their tidal rhythm after three days of captivity.