Immune response genes and pathogen presence predict migration survival in wild salmon smolts

We present the first data to link physiological responses and pathogen presence with subsequent fate during migration of wild salmonid smolts. We tagged and non-lethally sampled gill tissue from sockeye salmon (Oncorhynchus nerka) smolts as they left their nursery lake (Chilko Lake, BC, Canada) to compare gene expression profiles and freshwater pathogen loads with migration success over the first ~1150 km of their migration to the North Pacific Ocean using acoustic telemetry. Fifteen percent of smolts were never detected again after release and these fish had gene expression profiles consistent with an immune response to one or more viral pathogens compared with fish that survived their freshwater migration. Among the significantly up-regulated genes of the fish that were never detected post-release were MX (Interferon-induced GTP-binding Protein Mx) and STAT1 (Signal transducer and activator of transcription 1-alpha/beta), which are characteristic of a type I interferon response to vir...