Abstract
The influence of reward level on vertical distribution and growth was examined in rainbow trout fed on demand with self-feeders. Groups of 15 trout with initial body weight of 140 g were maintained at 14°C and feed access was restricted to a 12-h photophase. The trout received three reward levels with triplicates: 0.051 (low), 0.089 (medium) and 0.267 g/kg fish/trigger actuation (high). Vertical distribution in the higher reward groups was generally more even than that in the lower-reward groups, but the behavioral characteristics of some individuals in a group could play an important role in determining vertical distribution. Moreover, no fish including the individuals responsible for trigger actuation, occupied the vicinity of a trigger. The small groups of 15 trout receiving the medium-reward level obtained as much feed and grewas fast as the high-reward groups, but this was not the case for the low-reward groups.
