Prior residence, aggression and territory acquisition in hatchery‐reared and wild brown trout

In an artificial stream environment, established wild brown trout initiated 44% of the mean aggressive acts whilst hatchery‐reared trout initiated 34% and introduced wild trout initiated 22%. Established wild fish maintained home stations closer to a point source of feed than did both hatchery‐reared and introduced wild conspecifics. Established wild fish were the only group to show a positive mean specific growth rate during the trials. Introduced wild fish showed a slightly negative mean specific growth rate, whilst introduced hatchery‐reared fish exhibited a considerable negative mean specific growth rate. These results suggest that established wild brown trout in a semi‐natural stream environment display a prior‐resident effect over late introductions of hatchery‐reared and wild conspecifics. Introduced hatcheryreared fish were more aggressive and exhibited a lower mean specific growth rate than simultaneously stocked wild fish, suggesting that excessive expenditure of energy for unnecessary aggression may contribute to the poor survival of hatchery‐reared fish after they are stocked into streams.