Thesis (Ph.D., Biology)--University of Idaho, June 2014 | Post-spawned female rainbow trout were developed as a model for studying repeat spawning in steelhead kelts. Female trout were collected after spawning and separated into a standard maintenance ration group and a restricted ration group (20% of standard ration). Our intention was to induce an energy deficit that would arrest rematuration among restricted-ration fish, and then compare plasma levels and tissue gene expression for candidate endocrine biomarkers between non-rematuring and rematuring fish. Food-restriction arrested ovarian growth and development within 15-20 weeks, as evidenced by reduced ovarian growth and lower plasma estrogen levels. Food restriction also affected hepatic expression of the metabolic endocrine factors insulin-like growth factor and leptin, but not consistently across age classes, and did not affect circulating levels of nesfatin-1 or ghrelin. Next, we combined plasma hormone assays, physical measurements, and post-release tracking data for female steelhead kelts from a reconditioning program on the Yakima River to predict early detection of reproductive maturation. Rematuring kelts were longer and heavier at intake in spring; grew faster during summer reconditioning; and were longer, heavier, fatter, and of higher condition factor at autumn release. This work is the first known comparison of reconditioned steelhead with natural-origin in-river migrating steelhead, and shows that reconditioning projects yield bigger and fatter fish, with higher circulating levels of estrogen and similar circulating levels of vitellogenin compared to in-river migrating steelhead, and that tracking data suggests rematuring reconditioned kelts behave congruently with repeat spawning in the Upper Yakima River.