Genetic Evidence of Vertical Transmission and Cycling of Yersinia ruckeri in Hatchery-Origin Fall Chinook Salmon Oncorhynchus tshawytscha

Abstract

Abstract Enteric redmouth disease, caused by the bacterium Yersinia ruckeri, can be a severe problem in the culture of salmonid fishes, and can persist as a chronic infection within hatchery facilities for an indefinite amount of time ranging from months to years. Using a nested polymerase chain reaction (nPCR) assay and a real-time quantitative PCR (qPCR) assay, the prevalence of Y. ruckeri deoxyribonucleic acid (DNA) was documented across a single production cycle of fall Chinook salmon Oncorhynchus tshawytscha reared at a hatchery. Ovarian fluid from spawning female adults, unfertilized eggs, eyed eggs, sac fry, and juvenile fish all tested positive for Y. ruckeri DNA using both nPCR and qPCR assays. Presence of Y. ruckeri DNA in ovarian fluids and unfertilized eggs indicates that vertical transmission of the pathogen from females to their progeny is possible. Juvenile fish had the highest level of Y. ruckeri DNA at a log10-transformed level of 4.3 DNA copies per gram of kidney tissue. The limited mortality observed was attributed to handling and hatchery procedures during the study period and indicates that the low levels of the pathogen's DNA can persist without severe detrimental effects over the hatchery rearing cycle.