Evidence for reduced reproductive success (RS) of wild spawning hatchery-reared fish invites serious consideration with regard to the detrimental effects on subsequent generations of wild populations. Mate choice was evaluated as a potential mechanism contributing to these observed RS differences using a previous pedigree of wild spawning hatchery-reared and wild origin coho salmon (Oncorhynchus kisutch). Genetic variance at immune-relevant genes was used as ametric toexaminematechoice. Twoyears (2005 and2006)of threewild spawning mate pair classes were examined: wild x wild (W x W), hatchery x hatchery (H x H), and wild x hatchery (W x H). We tested for: (1) a departure from random expectations with regard to mate pair allelic diversity at immune-relevant markers, (2) a correlation between immune-relevant gene diversity and mate pair RS, and (3) distinguishable differences between mate choice strategies used by hatchery-reared and wild origin coho. Eight immune-relevant gene-linked microsatellite markers were used to evaluate mate choice; four linked to immune-relevant expressed sequence tags (ESTs) and four linked to the Major Histocompatibility Complex (MHC). We found evidence for non-random mating between 2006 W x H mate pairs at BHMS429,an MHC-linked marker, and at SsalR016TKU,an immune-relevantEST-linked marker, which was identified as a vasodilator-stimulated phosphoprotein. Non-random mating was also evident between 2005 H x H pairs at SsalR015TKU,an immune-relevantEST-linkedmarker,thoughno putativegene was identified. All other pair classes did not display a significant mate choice signature. We found a significant correlation between mate pair RS and immune gene diversity among 2005 and 2006 W x W mate pairs as well as 2006 W x H mate pairs. Notably, H x H mate pair RS was not correlated to immune gene diversity in either year. Results suggest that mate choice and genetic compatibility may influence fitness of wild spawning coho. / Graduation date: 2013