MONITORING THE FEEDING-ACTIVITY OF INDIVIDUAL FISH WITH A DEMAND FEEDING SYSTEM

Feeding activity of individual Arctic charr (Salvelinus alpinus) was recorded automatically for 29 days using a demand feeding system. Each of three groups of 15 fish was kept in 1 m3 tanks, containing brackish water at 10° C. Individual biting activity was continuously monitored using a PIT‐tag (Passive Integrated Transponders) system with unique individual codes. The accuracies of the bite detection system were 91, 93.1 and 99.5% respectively, in the three tanks. In all tanks, most of the individuals (12–14) bit on the releasing trigger a few times during the first 3 days. Thereafter, one or two individuals per tank accounted for almost all of the biting activity. This pronounced shift in bite‐number distribution among individuals was probably due to the development of a dominance hierarchy, in which the dominant individuals monopolized the trigger. Growth rates appeared to be highest among high ranking fish. The implications of using demand feeding and PIT‐tag devices in feeding studies are discussed. Copyright © 1993, Wiley Blackwell. All rights reserved