Effects of Simultaneous vs. Sequential Settlement on the Territorial Behaviour of Juvenile Rainbow Trout (Oncorhynchus mykiss)

The aggression hypothesis predicts that territories will be smaller and more numerous when individuals arrive simultaneously rather than sequentially, because of the prior residency effect, whereas the attraction hypothesis predicts the opposite. In this study, we test the predictions of these contrasting hypotheses by releasing 12 juvenile rainbow trout (Oncorhynchus mykiss) either simultaneously, all on 1 d, or sequentially, two per day for 6 d, in artificial streams. After the fish spent an average of 1 wk in the streams, we quantified the number of territories established, territory size, aggression rate and growth rate. There was evidence of a prior residency effect – early arrivers were more aggressive and grew faster than late arrivers – but this effect did not alter the number or size of territories established. We concluded that the temporal patterns of arrival have no strong effects on the territorial dynamics of juvenile rainbow trout.