Behaviour of rainbow trout (Oncorhynchus mykiss) under defensible and indefensible patterns of food delivery |
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| Authors: | M Saeed Heydarnejad G J Purser |
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| Institution: | (1) School of Marine Biosciences, Kitasato University, Ofunato Iwate, 022-0101, Japan;(2) Iwate Fisheries Technology Center, Kamaishi Iwate, 026-0001, Japan; |
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| Abstract: | The goal of this study was to investigate the behaviour of rainbow trout (n=30), Oncorhynchus mykiss, in small raceways when either self-feeders (T2) or hand-feeding (t2) were used. The method of food delivery in T2 was defensible
while that of t2 was indefensible. Fish in both raceways were subjected to restricted feeding (RF) for 25 days. Food was available
in the morning (09:00–10:00) in the downstream area and in the afternoon (16:00–17:00) in the upstream area of the raceways.
The results showed that the behaviour of rainbow trout was significantly different under interference competition (T2) for
food compared with that under scramble competition (t2). RF in T2 fish limited food availability to meal times when feeding
rewards were available while t2 fish only responded to the location of food delivery. The aggressive fish in T2 were dominant,
and t2 fish at high densities showed intense social interactions under the indefensible pattern of food distribution; these
interactions did not dampen to a minimum level to suppress the development of dominance hierarchies. Further, the stocking
density did not break down the dominance hierarchies between the T2 fish. This suggests that decreased efficiency in the search
for food or inefficient foraging, induced by interference competition at high densities, affected the behaviour of rainbow
trout. |
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