Examining the daily feeding rhythms of amago Oncorhynchus masou masou using self-feeding systems

Knowledge of circadian feeding rhythms in farmed fish species can help farmers determine the optimal feeding times to maximise feed consumption and minimise feed wastage. This study examined i) the circadian feeding rhythms, ii) the inter-day variability in feed demanded and iii) feed wastage of amago, Oncorhynchus masou masou, fed using self-feeding systems. Three replicate groups of 16 fish were held under a 12:12 light:dark cycle at 16 degrees C for 56 days. After a 28-day self-feeder acclimation period all three groups had become competent self-feeders and the treatment period ran from day 28 to day 56. Under the experimental light and temperature regime utilised amago appear to be visual self-feeders, actuating self-feeders almost exclusively during the light phase (99.9% of actuations). All three groups exhibited a distinct diurnal feeding rhythm within the light phase and demonstrated significant (P < 0.05) crepuscular peaks in feed demand. In addition, one group also displayed a significant peak at midday. Daily ration varied both within and between groups but no clear rhythmicity was observed in these variations. Feed waste was very low (always < 2%) for each group. The results of this study suggest that farmers can optimise daily feed consumption by feeding amago exclusively during the light phase, specifically at dawn and dusk, with a possible extra meal at midday. (C) 2011 Elsevier B.V. All rights reserved.