We describe the specific silencing of reporter gene lacZ in FHM cells (muscle cells of fathead minnow, a fish cell line) by either expressing small hairpin RNAs (shRNAs) from plasmids or transfecting small interfering RNAs (siRNAs) transcribed in vitro. Two types of dsRNAs could inhibit reporter gene expression, and siRNAs were more effective, while both of them worked very well in HeLa cells. siRNAs were tested for silencing expression of the major capsid protein (MCP) encoded by tiger frog virus (TFV), an iridovirus causing severe disease in fish. siRNAs targeting mcp gene effectively inhibited TFV replication in fish cells as demonstrated by reduced mcp RNA level, postponed emergence of cytopathogenic effect, as well as reduced TFV titer and particles in cells. The results suggest that the siRNA method suppressed TFV efficiently in fish cells, providing a potential approach to the therapy of aquaculture viral diseases.