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 hatchery-reared 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. (C) 1999 The Fisheries Society of the British Isles.