An evaluation of rearing densities to improve growth and survival of hatchery spring Chinook salmon

We evaluated growth and survival of spring Chinook salmon (Oncorhynchus tshawytscha) reared at varying densities at Warm Springs National Fish Hatchery, Oregon. For three consecutive brood years, density treatments consisted of low, medium, and high groups in 57.8 m3 raceways with approximatly16,000, 24,000, and 32,000 fish/raceway, respectively. Fish were volitionally released in both the fall and spring to mimic the downstream migration timing of the endemic wild spring Chinook salmon stock. Just prior to the fall release, the rearing density estimate was 4.24 kg/m3 for the low density group, 6.27 kg/m3 for the medium density group, and 8.42 kg/m3 for the high density group. Weight gain did not differ among density treatments (P = 0.72). A significant difference was found in median fork length (P <0.001) for fish reared at different densities in the one year length was measured in the fall. Fish reared at high density exhibited the highest on-hatchery mortality rate during two broo...