Persistence of Largemouth Bass Virus Infection in a Northern Mississippi Reservoir after a Die-Off

Abstract

Approximately 3,000 adult largemouth bass Micropterus salmoides were found dead in September 1998 in Sardis Reservoir, Mississippi. Investigation of largemouth bass electrofished 1 month after the reported losses revealed a high level of infection with largemouth bass virus (LMBV) in the population. Subsequent sampling on five separate occasions during the following year revealed that approximately one-half of the fish were positive for LMBV 7 months after the die-off. On the last sampling, 13 months after the die-off, approximately one-third of bass cultured positive for LMBV. The most common finding associated with LMBV infection was a yellow waxy substance in the swim bladder that consisted of erythrocytes and eosinophils in a fibrin clot indicating previous hemorrhage. In nearly every case, fish that had the swim bladder lesion cultured positive for LMBV. Predisposition to infection did not correlate with the gender or size of the fish. Sympatric white bass Morone chrysops, white crappies Pomoxis annularis, bluegills Lepomis macrochirus, and gizzard shad Dorosoma cepedianum were also evaluated and found to be negative for LMBV. This study is the first report of a high level of LMBV infection and long-term LMBV persistence in a largemouth bass population in Mississippi and provides circumstantial evidence suggesting that the largemouth bass–specific losses were LMBV associated.