Pen Rearing and Imprinting of Fall Chinook Salmon, 1984 Annual Report.

Backwaters and ponds along the Columbia River upstream of production hatcheries may provide opportunities for creating low cost rearing facilities and additional space to accommodate hatchery-thinning releases.Upriver bright, age-0 fall Chinook salmon (Dnchorynchus tshawaytsha) were transferred from Spring Creek National Fish Hatchery in mid-April to rearing sites located 62 and 125 miles upstream from the hatchery and reared in netted enclosures for 6-8 weeks prior to release.All fish reared at the off-station sites displayed increased growth rates and accelerated smoltification rates when compared to fish held in the hatchery.Highest growth rates were for fish reared in net pens at low densities and full feeding rations but more fish per unit volume were obtained when reared at higher density and a full feeding ration.Increased mortalities were associated with an outbreak of enteric redmouth disease (Yersinia ruckeri) when temperature exceeded 16 C, especially for fish reared at high density.Density of unfed fish stocked in a barrier net and net pens was low in relation to those of fed fish, but the natural food available was adequate for growth in excess of that observed in the hatchery.Mortality was relatively high (30%) in the barrier net, less than 1% for unfed fish in pens, and ranged from about 1% to 16% for fed fish in pens.