The Relation of Largemouth Bass Virus to Largemouth Bass Population Metrics in Five Alabama Reservoirs

Abstract

Between the early to mid-1990s and 1998–2000, angler and electrofishing catch rates of memorable-size (≥2.27-kg or 51-cm) largemouth bass Micropterus salmoides declined 3–20-fold in five Alabama reservoirs. Largemouth bass virus (LMBV) has been implicated in widespread fish kills of this species, and we documented the prevalence of LMBV and attempted to quantify the impact of LMBV on growth, body condition, and size and age structure to account for the loss of memorable-size fish in these five populations. Fish were collected primarily with electrofishing between 2000 and 2002, and two methods were used to detect LMBV from Lakes Wheeler, Demopolis, Eufaula, Guntersville, and Weiss. Among these five reservoirs, LMBV infection was most common in fish that ranged from about 25 to 40 cm and in young to intermediate-age fish (range = 1–2 to 6 years). The virus was rare in fish under 100 mm (age 0) and over 500 mm (≥age 7). Fish infected with LMBV generally had lower relative weight and grew more slowly after age 3 than uninfected fish. The prevalence of LMBV was not as great in older and larger fish, possibly because these fish died prior to our collection. The decline in memorable-size fish in these five reservoirs in the late 1990s to 2000 was due to slower growth, poorer body condition, and increased mortality of older fish and was circumstantially linked to LMBV. However, the prevalence of LMBV in the Lake Eufaula population was nil after 2001, whereas a fish kill was associated with LMBV in 1997. None of 349 fish we assayed from Lake Eufaula in 2002 were infected with LMBV, growth rates improved, and memorable-size fish were more common in electrofishing samples and angler catches in 2003. Although we could not definitively demonstrate that LMBV caused the loss of memorable-size largemouth bass in Alabama reservoirs, the virus appeared to be linked to this phenomenon.