Competitive ability and social behaviour of juvenile steelhead reared in enriched and conventional hatchery tanks and a stream environment

Steelhead Oncorhynchus mykiss fry reared in an enriched hatchery environment (overhead cover, submerged structures and underwater feeders) and a natural stream both achieved significantly greater social dominance ranks than fry reared in a conventional hatchery environment. Dominant fry from enriched tanks and natural stream exhibited greater frequencies of threat displays than dominant fry reared in conventional tanks. Fry reared in the natural stream exhibited greater territory overlap than fry from either hatchery environment. Overall, the results suggest that enriched hatchery environments may act to ameliorate some but not all changes in social behaviour that result from hatchery rearing.