Evaluation of Nonlethal Sampling Techniques for Infectious Hematopoietic Necrosis Virus in Steelhead Oncorhynchus mykiss

Prior to moving or liberating fish from a hatchery, a subset of the population is sampled for pathogens to identify risks to the receiving facility/body of water.  Standard protocols consist of lethal sampling, which can create unnecessary impacts on highly valued or endangered fish.  Although nonlethal samples for viruses of concern have been evaluated, many studies used pathogen specific molecular assays, which are more sensitive but only detect genetic material. We used cell culture, which can detect replicating agents of multiple virus types and we compared three nonlethal sampling methods (mucus/skin scrape, pectoral fin tissue and gill tissue) to a standard lethal sample (pooled kidney and spleen tissue).  During two spawning seasons, samples were collected from steelhead (Oncorhynchus mykiss) broodstock at the Dworshak National Fish Hatchery historically demonstrating natural infections with infectious hematopoietic necrosis virus (IHNV). Though the study is ongoing, preliminary results indicate that mucus and fin preparations were more sensitive at detecting IHNV than kidney/spleen or gill tissues. Detection of live viruses in the mucus or fin may not indicate an infected individual, but the survey method is useful for determining the risk of pathogen transfer in a population of fish.