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***SEE ATTACHED SOW, COMBINED SYNOPSIS AND SF18 FOR COMPLETE DETAILS, INCLUDING TERMS AND CONDITIONS*** Background/Overview: Thiamine Deficiency Complex (TDC) is a nutritional deficiency of thiamine (... ***SEE ATTACHED SOW, COMBINED SYNOPSIS AND SF18 FOR COMPLETE DETAILS, INCLUDING TERMS AND CONDITIONS*** Background/Overview: Thiamine Deficiency Complex (TDC) is a nutritional deficiency of thiamine (vitamin B1) recently linked with high mortalities of early life stage spring- and fall-run Chinook salmon in Central Valley (CV) hatcheries and coho salmon in the Klamath Basin at Iron Gate Hatchery. Clinical signs of TDC are anorexia and sporadic spinning prior to death (Lee et al. 2009; Ketola et al. 2000). Offspring of female salmon with reduced levels of thiamine are prone to TDC. The current hypothesis: a narrowing of the diversity of salmon marine diet and/or a more southerly ocean distribution where prey are either deficient in thiamine levels or high in thiaminase (Northern anchovies). Thiaminase is an enzyme that destroys or inactivates thiamine, and has been identified as the primary explanation for low levels of thiamine and the subsequent onset of TDC in Great Lakes and Baltic Sea salmonids. There is an urgent need to document the scope of TDC by directly assessing egg-thiamine concentrations in California’s salmonids. To date, TDC in hatchery fish has been inferred from unusual fry behavior, higher than normal fry mortality rates, and rapid positive fry responses to thiamine bath treatments. However, the extent of both lethal and sub-lethal TDC is unknown. Likewise, although evidence supports thiaminase consumption as a causative factor for TDC in fishes, research is still needed to identify and describe ecological and environmental factors linked to ocean processes that may influence the manifestation of TDC. Investigating under what conditions thiamine deficiency occurs for salmon in natural systems will support development of predictive and preventative management strategies. We propose to document the scope of TDC in Pacific salmonids in the Klamath Basin. The proposed activity is to measure the thiamine concentration in broodyear 2020 Chinook salmon, coho salmon, and steelhead eggs from Klamath Basin hatcheries and from Chinook salmon collected from lower Klamath River fisheries. Once collected, egg samples will be shipped for analysis of egg thiamine concentrations (each sample: 10 g per female). Funding has been acquired to support sampling and analysis of CV Chinook salmon. This is a comparison study to the funded effort for Central Valley Chinook salmon to provide insight to the prevalence of TDC in the Klamath Basin and provide within basin (Central Valley and Klamath Basin) and regional context of TDC to inform conservation and management actions of Pacific salmonids. Scope of Work Free-flowing eggs collected at two Klamath Basin hatcheries (Chinook salmon, coho salmon, and steelhead) and eggs collected from Chinook salmon in the lower Klamath River will provide a synoptic view of the scope of TDC in populations of anadromous fish in the Klamath Basin. Egg samples from Chinook salmon, coho salmon, and steelhead (10g of eggs per individual fish) will be collected by NMSF scientists and collaborators. Samples will be shipped on dry ice to contractor where they will be stored at -80? prior to biochemical analysis. Total number of individual samples will be 300 (30 individuals from six hatchery populations and four lower river groups of Chinook salmon).