EFFECTS OF RESTRICTED RATION, TIME-RESTRICTED ACCESS AND REWARD LEVELON VOLUNTARY FOOD-INTAKE, GROWTH AND GROWTH HETEROGENEITY OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) FED ON DEMAND WITH SELF-FEEDERS

Growth responses of rainbow trout fed on demand using self-feeders wer e tested over an 8 week period when triplicate groups were exposed to two feeding levels (unlimited and fixed ration), at two feeding freque ncies (tine-restricted and free access) and three reward levels (0.17 g, 0.30 g and 0.43 g per trigger actuation). Triplicate groups were al so hand fed as control of maximum growth. Each fish was marked accordi ng to its weight-class, and each group of 26 fish comprised a predeter mined number of fish per weight-class: two fish of 13-16 g, six fish o f 16-19 g, 10 fish of 19-22 g, six fish of 22-25 g and two fish of 25- 28 g. There was no significant effect of feeding regime on feed effici ency. Voluntary feed intake and specific growth rates were significant ly decreased as fish were exposed to reduced reward levels, even thoug h there was a negative relationship between reward level and daily dem and. Time-restricted access to self-feeders led to a decrease in feed intake, and an increase in growth heterogeneity in comparison with fre e access to self-feeders. Voluntary feed intake and specific growth ra tes were always lower in self-fed groups than in groups fed to apparen t satiation by hand. Individual growth heterogeneity was greater withi n tanks allowed time-restricted access to self-feeders and within tank s fed by hand to visual satiation than within those given continuous a ccess to self feeders. It is suggested that rainbow trout fed on deman d with self feeders may not ingest as much food as they would be able to, and may not be satiated, but do express their hunger in relation w ith the level of effort that has to be done to obtain food. (C) 1998 E lsevier Science B.V. All rights reserved.