The Effect of Juvenile Rearing Density on Adult Returns of Summer Steelhead

Juvenile steelhead Oncorhynchus mykiss were reared at two hatcheries in an attempt to determine the influence of loading (kg · L −1 · min −1 ) and density (kg/m 3 ) on adult survival. At one hatchery in which fish were reared and released from raceways for 3 years, there was no significant difference in recovery rates of fish reared at levels 20% below normal loadings and densities compared with those reared at 20% above normal loadings and densities. At a second hatchery in which fish were reared in ponds for 3 years before release, flows were adjusted so that loadings were similar but densities differed; a significant decrease was observed in returns of test fish when loading was 2.1 kg · L −1 · min −1 and density was 5.8 kg/m 3 , and returns greatly decreased when test fish loading was 2.3 kg · L −1 · min −1 and density was 6.3 kg/m 3 .