Gut Microbiota Diversity of Pre-Smolt Hatchery Steelhead (Oncorhynchus mykiss) Across the Cascade Divide

The Pacific Northwest is known for its once-abundant wild salmonid populations, but they have been declining for more than 50 years due to habitat destruction and commercial overexploitation. To compensate, federal and state agencies annually release hundreds of thousands of hatchery-reared fish into the wild.   Despite these measures, accumulating data indicates hatchery fish have lower fitness in natural environments compared to wild fish, and effects of early life in freshwater habitats appear to be a key factor influencing return rates of anadromous salmonids. Recently, mounting evidence indicates the richness and diversity of intestinal microbial species influence the development of the gut and immune system. Our research addresses the connection between intestinal microbiota of anadromous fish and its effect on their viability in the wild. We examined the gut microbiota of pre-migratory hatchery-reared steelhead (Oncorhynchus mykiss) to asses gut microbial diversity that could potentially lead to differences in return rates. Moreover, the Cascade Mountains serves as an allopatric border between two distinct lineages of steelhead that show significant differences in genomic and mitochondrial diversity; will differences in core microbiota of hatchery-reared fish correlate with this genetic phylogeny? The gut microbiota seeded in hatchery environments is likely not as suitable for digestion of wild foodstuffs and may negatively impact gut development, possibly impeding smoltification and migration. The identification of a core gut microbiota common to hatchery-reared steelhead is a first step in determining if hatchery environments and diets can be adjusted to better prepare hatchery stock for life in wild environments.