Effects of restricted ration, time-restricted access and reward level on voluntary food intake, growth and growth heterogeneity of rainbow trout ( Oncorhynchus mykiss) fed on demand with self-feeders

Abstract

Growth responses of rainbow trout fed on demand using self-feeders were tested over an 8 week period when triplicate groups were exposed to two feeding levels (unlimited and fixed ration), at two feeding frequencies (time-restricted and free access) and three reward levels (0.17 g, 0.30 g and 0.43 g per trigger actuation). Triplicate groups were also hand fed as control of maximum growth. Each fish was marked according to its weight-class, and each group of 26 fish comprised a predetermined number of fish per weight-class: two fish of 13–16 g, six fish of 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 efficiency. Voluntary feed intake and specific growth rates were significantly decreased as fish were exposed to reduced reward levels, even though there was a negative relationship between reward level and daily demand. Time-restricted access to self-feeders led to a decrease in feed intake, and an increase in growth heterogeneity in comparison with free access to self-feeders. Voluntary feed intake and specific growth rates were always lower in self-fed groups than in groups fed to apparent satiation by hand. Individual growth heterogeneity was greater within tanks allowed time-restricted access to self-feeders and within tanks fed by hand to visual satiation than within those given continuous access to self feeders. It is suggested that rainbow trout fed on demand 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 with the level of effort that has to be done to obtain food.