The effects of largemouth bass virus on a quality largemouth bass population in Arkansas.

A 22.4-ha impoundment experienced an outbreak of Largemouth bass (Micropterus salmoides) virus (LMBV) disease in the summer of 2006. All dead or dying largemouth bass observed throughout the entire event were recorded and removed. In this study, we estimated mortality and examined size distribution, condition, and biomass following the outbreak. Boat-mounted electrofishing was used to collect largemouth bass for a mark-recapture population estimate and other population metrics. Fish samples were examined for evidence of LMBV, other infectious diseases, and physical abnormalities. Cell cultures inoculated with samples from moribund fish developed cytopathic effects typical of LMBV, and polymerase chain reaction (PCR) confirmed the presence of LMBV. The total number (N+/-95% confidence interval) of stock-size largemouth bass remaining was estimated to be 2,301+/-528 fish (103 bass/ha). The total observed mortality, including dead and dying individuals, during the LMBV outbreak was 176 largemouth bass (7% of the initial population). The total biomass remaining was estimated at 1,592 kg of stock-size bass and a relative biomass of 71.5 kg of stock-size largemouth bass per hectare. Largemouth bass size structure was dominated by quality and preferred (300-510 mm) size classes, with very few memorable-size or larger (>510 mm) fish, and the relative weight of largemouth bass was unusually variable. These results demonstrate that largemouth bass abundance and biomass in the reservoir remained very high despite mortalities attributed to a LMBV outbreak.