Mapping the demand-feeding pattern of hatchery-reared rainbow trout, Oncorhynchus mykiss (Walbaum)

Fish fed using demand feeders often display highly variable feeding activity across days. In order to quantify this pattern, data from 10 groups of self-feeding rainbow trout, Oncorhynchus mykiss (Walbaum), with a mean start weight of 30–120 g were examined for repeating patterns using time series analysis. The number of bites on a self-feeding trigger were recorded and summarised on both an hourly and daily basis. Significant peaks in trigger-biting activity occurred in the morning and evening at lights on and lights off. It is suggested that this activity pattern corresponds to an evolutionary trade-off between predation risk and feed availability. Across days, peaks in trigger-biting activity are significantly higher every second day. A possible explanation for this pattern is the time required for gastric evacuation and the return of appetite.