Assessment and analysis of smolt condition in the Columbia River Basin / Volume 1: Evaluation of the effect of a modified feeding strategy on growth and smoltification of summer steelhead (Oncorhynchus mykiss) at Dworshak National Fish Hatchery

The primary objective of the study was to increase the number of summer steelhead (Oncorhynchus mykiss) from Dworshak National Fish Hatchery that outmigrate by promoting smoltification in a larger proportion of the production release. To achieve this goal, growth was reduced during the winter to produce a smaller size range of fish to eliminate the production of large fish that residualize. A period of accelerated growth prior to release was designed to promote smoltification in all fish, regardless of size. Decreased winter growth was achieved with a combination of reduced ration and short, intermittent feeding periods. Growth rates were not reduced to the expected level in the modified feeding schedule treatment group, control group, or general production fish reared in the same system. Although significant differences in length, weight and condition factor developed between treatment and control groups during December and January, compensatory growth of the treatment fish after return to full rations resulted in fish of the same size from both groups for release. Migration rates of the treatment group were higher than that of the control group, although the difference was not significant. Growth and survival during extended seawater rearing did not differ between the two groups. Smoltification, as measured by gill Na+, K+-ATPase and seawater survival, were unaffected by a reduction in feed during winter months