Temperature preference of 2-14 month old striped beakperch, Oplegnathus fasciatus, (B. L. 3.3-14.9cm) hatched on the same day was tested using a vertical temperature gradient tank. Fish were acclimated to 25°C for more than 18 days before the experiments. Temperature was a dominant factor affecting fish distribution in a vertical temperature gradient, since the distribution was shifted in accordance with the location of preferred temperature. No clear change in the preferred temperature was shown with exposure to the temperature gradient for more than 24 hours. The preferred temperatures were related to the growth of the fish. Two to eight month old fish preferred a progressively cooler temperature from 28.6 to 24.7°C as they grew. Fish older than 8 months preferred a narrower temperature range of 25 and 26°C.
