Abstract
Fish cells derived from rainbow trout gonad or Atlantic salmon are sometimes damaged by the relatively high temperature of agar overlay widely used for plaquing animal viruses. This heat-induced cell damage can be avoided by the use of gum tragacanth, which may be applied at room temperature. When the medium was buffered with tris(hydroxymethyl)aminomethane-hydrochloride and NaHCO3, the plaque assay could be performed without the use of a CO2 incubator. Using this method, a number of animal viruses were plaqued on a variety of cell monolayers at different temperatures under atmospheric conditions.