Dualistic feeding pattern of Nile tilapia (Oreochromis niloticus, L.) reared under different self-feeding system conditions

摘要

Nile tilapia (Oreochromis niloticus) is one of the most important cultured species worldwide. The research aims to clarify the feeding characteristics, such as daily feeding pattern of Nile tilapia using a self-feeding technique. The feeding pattern was conducted under two rearing conditions, indoor treatments under a controlled light regime (LD 12:12) and constant water temperature (25 degrees C), and outdoor treatments under natural conditions which consisted of duplicate trials with two periods each. The outdoor treatment was carried out from early summer through late autumn in Mie, Central Japan. Daily self-feeding activity of Nile tilapia in indoor treatments was nearly daytime feeding pattern, synchronizing with the given photoperiod (24hr). However, the self-feeding activity in the outdoor experiments from early summer to early autumn was almost daytime feeding pattern, but it became less clear and shifted to a nighttime feeding profile in late autumn. The results revealed that Nile tilapia has a dualistic capacity for demand-feeding both in light and dark phases. These results might have been caused by the seasonal change in light intensity and/or water temperature. Information obtained from the self-feeding experiments enables us to identify the influence of environmental changes on the physiological condition of farmed fish through their expression of appetite.