Wide-scale disease-related mortality of young-of-year (YOY) smallmouth bass was first documented in 2005 and has occurred annually at varying degrees since that time. Repeated mortality events and variable recruitment from natural conditions (i.e. high June-July stream discharges) have resulted in a decline in the adult smallmouth bass population in this locally economically important recreational fishery. Factors including water quality and parasite pathogens have been associated with secondary bacterial infections that are characteristic of outbreaks among YOY smallmouth bass. Largemouth Bass Virus (LMBV) has been consistently isolated from moribund smallmouth bass specimens submitted for viral analysis. The objective of the proposed study is to determine whether LMBV isolates from the Susquehanna River Basin are pathogenic to YOY smallmouth bass and at what concentration (LD50) in a laboratory setting. Further, the role that temperature and co-occurring opportunistic bacteria play in inducing clinical disease in YOY smallmouth bass will be investigated.