Tissue composition, condition and energy storage in mature hatchery origin steelhead trout from the Snake River, ID

Little information is available describing the condition of vital organs or the storage and mobilization of energy reserves in mature and post-spawn (kelt) steelhead trout.  In 2009 and 2010, we examined the condition and tissue composition of sexually mature steelhead from Dworshak National Fish Hatchery, ID and compared these fish to migrating hatchery-origin kelts at Lower Granite Dam, WA.  In 2010 maturing Dworshak steelhead were also sampled at four periods to measure tissue composition and condition with advanced sexual maturity.  We assessed organo-somatic indices, measured the proximate content of liver and white muscle tissue, and sampled vital organs for histological analysis.  Preliminary results for 2009 show that all organo-somatic measures were significantly higher (Wilcoxon P: < .001) in migrating kelts than fish collected at the time of spawning.  Lipid content of the livers for all fish was low ranging from 1.14% to 4.46% of wet weight.  Protein content of livers ranged from 12.79% to 24.08% of wet weight.  Total liver energies calculated from emigrating kelts at Lower Granite Dam ranged from 3.44 to 5.51 kJ/g of wet weight.  These results will be paired with non-lethal measures of condition to provide management tools for increasing survival and iteroparity of this species.