Demand feeding as a self-regulating feeding system for rainbow trout ( Oncorhynchus mykiss) in net-pens

Abstract

Rainbow trout with an initial weight of 1.1 – 1.2 kg were fed an extruded high energy food using demand feeding and timer-controlled feeding techniques, during 4 summer months, in full-scale netpen farming conditions. Unrestricted and restricted demand feeding techniques were tested. The time-rcontrolled feeding was tested at a corresponding restricted level. There were no statistically significant differences in growth rate between trout fed restricted and unrestricted rations using the demand feeding technique. Trout fed using the timer-controlled technique exhibited a significantly lower growth rate compared with fish fed using demand feeders. Trout fed using the demand feeding technique and restricted rations had the best feed conversion, with a mean value of 1.08 during the experiment (feed conversion = kg food supplied/kg weight gain). The feeding of trout using the unrestricted demand feeding technique resulted in a feed conversion of 1.49, and using restricted timer-controlled feeding it was 1.36. The feed conversion in the unrestricted demand feeding groups was correlated with water temperature, indicating that the ability of the trout to regulate the feeders at a level where food losses were minimized, was temperature dependent. It is suggested that the feeding of fish, using a timer-controlled technique and restricted food rations, with short and regular feeding intervals induces stress and high competition for food. This consequently leads to increased swimming activity and metabolic energy losses.