The lethal dose of largemouth bass virus in juvenile largemouth bass and the comparative susceptibility of striped bass

摘要

Largemouth bass virus (LMBV) is an iridovirus that was isolated from wild adult largemouth bass (Micropterus salmoides) in the southeastern USA in 1994. Although originally isolated from moribund wild fish, its virulence to juvenile largemouth bassis uncertain. To help clarify this point, 2 LMBV titrations were made in juvenile largemouth bass. Titres of LMBV in fathead minnow cells were 104.8 and 105.8 tissue culture infectious doses - 50% cytopathic endpoint (TCID50) per millilitre, respectively. Tenfold serial dilutions of LMBV employed in each cell culture titration, injected intraperitoneally (0.1 ml/fish) into largemouth bass produced calculated lethal dose - 50% mortality endpoints (LD50s) of 282 (102.45) and 288 (102.46) infectious dosesin 2 consecutive infectivity trials. Virus yield of assayed infected fish averaged 108.5 TCID50/g and 107.7 TCID50/g in viscera of moribund and dead fish in the 2 trials and 106.5 TCID50/g in surviving exposed fish 14 days after infection. In a second experiment, largemouth bass had 100% mortality 5 days after injection while virus immersed fish had a significantly lower mortality of 17% at 14 days. Similarly treated juvenile striped bass (Morone saxatilis) suffered 63% mortality after injection and significantly lower mortality of 10% after immersion. In a third study of 25 days, 100% of injected largemouth bass died by 5 days after injection, and all of them were virus-positive. Injected striped bass had a significantly lower mortality of 24%; all 3fish were virus-positive initially, 2 fish were virus-positive at 18 days, and none were positive at 25 days. Juvenile largemouth bass were highly susceptible to LMBV injection and striped bass were moderately susceptible, but both species were only mildly susceptible when exposed by immersion.