BEHAVIORAL-RESPONSE TO COMMERCIAL FOOD OF DIFFERENT SIZES AND SELF-INITIATED FOOD SIZE SELECTION BY ARCTIC CHAR

Reaction and handling times for Arctic char Salvelinus alpinus with re spect to feed pellets that varied in length or diameter were visually observed. Reaction time decreased and handling time increased with inc reasing pellet size, responses that were more pronounced with increasi ng diameter than with increasing length of the food particles. In tota l, fish missed or failed to respond to nearly 50% of the smallest and largest pellets offered to them. Also, we studied the ability of Arcti c char to choose among different sizes of pellets and to locate food o f optimal size. Three replicate groups of char each could release thre e demand feeders, each feeder delivering a different particle size (1. 7, 2.5, or 3.6% of fish fork length). After about 2 weeks, the proport ion of bites on the feeder that contained pellets close to the optimal size exceeded 70% of the total daily biting activity. This pattern wa s repeated in a series of experiments with different feeder positions, indicating a strong ability to locate feed of a preferred size. Daily frequencies of demand feeding bites varied considerably, and diel bit ing activity increased just before and after the lights went on or off .