Genetic immunization has proved effective in a number of applications including vaccination of rainbow trout (Oncorhynchus mykiss) against the fish pathogen infectious hematopoietic necrosis virus. However, injection vaccines, especially in aquaculture, are not as desirable as oral or immersion dosing schemes. In this report we present evidence that attenuated invasive Escherichia coli can infect and deliver plasmid DNA to salmonid fish cells.