THE FEEDING RESPONSE OF DIPLOID AND TRIPLOID ATLANTIC SALMON AND BROOK TROUT

Pair and group experiments were conducted to determine whether differe nces exist in feeding success between juvenile diploid and triploid sa lmonids in a competitive situation. In the pair experiments, 22 pairs (one diploid and one triploid) of size-matched Quebec-strain brook tro ut Salvelinus fontinalis (7.2-46.3 g) were fed an unlimited number of pellets three times a day for 5 days. Dominance was assigned to the fi sh which ate the most pellets within each pair. In the group experimen ts, groups of three diploid and three triploid size-matched fish were fed a restricted ration three times a day for 5 days. Hierarchical ran k within the group was assigned based on the number of pellets consume d by each fish. The group experiment was repealed 10 times with Atlant ic salmon Salmo salar (5.1-62.7 g), Quebec-strain brook trout (11.8-11 0.8 g), and large UNB-strain brook trout (18.2-33.0 g), and 12 times w ith smaller UNB-strain brook trout (0.6-2.0 g). A statistically signif icant difference in rank between ploidies was found only for the small er UNB-strain brook trout in the group experiments, with diploids domi nant over triploids. This suggests that there may be a difference in c ompetitive feeding success between diploid and triploid brook trout ea rly in development, but that this difference diminishes as the fish gr ow. (C) 1997 The Fisheries Society of the British Isles.