Use of gum tragacanth overlay, applied at room temperature, in the plaque assay of fish and other animal viruses.

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 ocnditions.