Ichthyophonus in Pacific herring: Investigating a transmission hotspot

Abstract

Chapter 1. Sample collection and processing methods were optimized and validated for the detection of Ichthyophonus DNA in environmental samples using both spiked and field samples. Methods performance testing revealed low efficiency in sediment samples, suggesting the extraction techniques were not yet effective for detecting Ichthyophonus DNA in spiked sediment samples. The optimized techniques worked well for spiked water samples, and in field application of the method, revealed presence of Ichthyophonus DNA in natural seawater samples collected from a known Ichthyophonus transmission hot spot in Cordova Harbor, AK. Chapter 2. A geographic hot spot of high Ichthyophonus infection prevalence occurred in juvenile Pacific herring from Cordova Harbor, AK, USA during 2015 and 2019. Over-winter infection prevalence (0-5%) was similar to that of juvenile herring in other locations; however, prevalence in Cordova Harbor increased rapidly during the spring, peaking at 64% (2015) and 40% (2019) in June and July. Reasons for the geographical hot spot remain undetermined, but seasonal shifts in herring diet were coincident with the changing infection prevalence in Cordova Harbor.