Short communication Examining the daily feeding rhythms of amago Oncorhynchus masou masou using self-feeding systems Matthew J. Flood a, d, ⁎, Chris Noble b , Rem Kagaya a , Børge Damsgård b , G. John Purser c , Mitsuo Tabata a a Division of Animal Science, Teikyo University of Science, 2525 Yatsusawa, Uenohara, Yamanashi 409-0193, Japan b Nofima Marin, Muninbakken 9-13, P.O. Box 6122, NO-9291 Tromsø, Norway c National Centre for Marine Conservation and Resource Sustainability, Australian Maritime College, University of Tasmania, Locked Bag 1370, Launceston 7250, Tasmania, Australia d Australian Bureau of Agricultural and Resource Economics and Sciences, Department of Agriculture, Fisheries and Forestry, GPO Box 1563, Canberra ACT, 2601, Australia abstract article info Article history: Received 2 December 2010 Received in revised form 29 April 2011 Accepted 4 May 2011 Available online 11 May 2011 Keywords: Self-feeding Amago Circadian feeding rhythms Production Welfare 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 °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 b 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 b 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. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Farmed fishes often exhibit species specific circadian feeding rhythms (Madrid et al., 2001). Whilst these rhythms often vary among seasons (Bolliet et al., 2001; Fraser et al., 1993) many studies have shown peaks in dawn and/or dusk feeding activity in salmonid species including rainbow trout, Oncorhynchus mykiss: Walbaum, 1972 (Sánchez-Vazquez and Tabata, 1998), Atlantic salmon, Salmo salar: Linnaeus, 1758 (Blyth et al., 1993; Kadri et al., 1991) and Arctic charr, Salvelinus alpinus: Linnaeus, 1758 (Alanärä and Brännäs, 1997). It is thought that these rhythms represent an evolutionary trade-off between food availability, predator risk, vision capacity and metabolic requirements (Eriksson and Alanärä, 1992; Metcalfe et al., 1999). As such, there is a certain degree of flexibility to these general trends. For example, although rainbow trout are usually crepuscular feeders (Sánchez-Vazquez and Tabata, 1998), they can also feed at either dawn or dusk (Noble et al., 2005) or can feed during the night (Landless, 1976) and this can be related to time of year, i.e. day length and water temperature (Madrid et al., 2001). It has been suggested that farmers should design feeding manage- ment strategies that match the natural feeding patterns of fish (Alanärä et al., 2001). Feeding in this way has been demonstrated by a number of authors to increase growth and improve feed conversion (Azzaydi et al., 1999; Bolliet et al., 2001; Boujard et al., 1995; Gelineau et al., 1996), and to minimise feed wastage (Bolliet et al., 2001) which improves the economic and environmental sustainability of aquaculture (Cho and Bureau, 1998). Demand feeding systems, i.e. self-feeders (Alanärä, 1992) and interactive feedback systems (Blyth et al., 1993), allow fish to feed whenever they desire. Self-feeders let fish demand feed by actuating a trigger (Adron et al., 1973) and can improve welfare by reducing aggression (Almazán-Rueda et al., 2004), stress (Endo et al., 2002) and fin damage (Suzuki et al., 2008), and improve production by improving growth (Suzuki et al., 2008) and feed conversion ratios (Alanärä, 1992) while minimising feed wastage (Noble et al., 2007a,b; Paspatis et al., 1999). Even when self-feeders are not used on farms they can be used experimentally to determine the preferred feeding times for a given species, providing farmers with baseline feeding rhythm data that can be used to develop robust feed management strategies which are in sync with natural feeding rhythms. Amago (O. masou masou: Brevoort, 1856) are a popular aquacul- ture species in Japan, grown in freshwater raceways and ponds. Aquaculture 318 (2011) 244–247 ⁎ Correspondence at: Australian Bureau of Agricultural and Resource Economics and Sciences, Department of Agriculture, Fisheries and Forestry, GPO Box 1563, Canberra ACT, 2601, Australia. Tel.: +81 90 2258 3754; fax: +81 554 63 4431. E-mail addresses: matthew.flood@abares.gov.au (M.J. Flood), chris.noble@nofima.no (C. Noble), kagaya@ntu.ac.jp (R. Kagaya), borge.damsgaard@nofima.no (B. Damsgård), jpurser@amc.edu.au (G.J. Purser), tabata@ntu.ac.jp (M. Tabata). 0044-8486/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2011.05.007 Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online