Energy Requirements and Feeding Behaviour of Salmonids in Culture

Bailey, J. 2003. Energy requirements and feeding behaviour of salmonids in culture. ISSN, 1401-6230, ISBN 91-576-6348-3 This thesis deals with the feeding management of salmonids, from the calculation of the daily feed requirement to the presentation and delivery of that ration taking into consideration the feeding behaviour. The digestible energy need (DEN) to grow 1 kg of wet body weight was calculated for different farmed fish species. In general, the DEN increased with increasing body weight. Using this information, a feed ration model was created and tested using rainbow trout (Oncorhynchus mykiss). Fish fed using this model showed a high rate of growth and a good feed conversion ratio (FCR). The model accurately predicted growth in trout and can be easily applied as a method of calculating the daily ration. For comparison, 3 groups were fed using self-feeders. These groups showed a pattern of fluctuating trigger-biting activity across days and this type of pattern was further studied using time series analysis for groups of rainbow trout. Peaks in activity occurred in the morning and evening at lights on and lights off. Across days, peaks in activity are significantly higher every second day. This pattern is probably a result of an “hourglass” mechanism such as the time required for gastric evacuation and the return of appetite. Knowing how much feed to give each day, one must then present it in an optimal way. Rainbow trout were fed the daily ration using various portion sizes and at different temperatures. At 5 oC, growth and FCR were best when small portion sizes were used. At higher temperatures, good growth rates and FCR were observed over a broader range, indicating a high level of plasticity in the trout’s ability to adjust to different portion sizes at higher temperatures. To further evaluate feed presentation, Atlantic salmon (Salmo salar L.) were raised in sea cages, and fed using different combinations of pellet sizes and delivery rates. Treatment groups were compared using growth rate. No significant linear effect on growth due to pellet size or delivery rate could be detected. For pellet size, however, indications point to a non-linear relationship with growth rate. Salmon grew equally well irrespective of treatment further indicating a high level of plasticity in the salmon’s ability to adjust to changes in feed presentation.