Strong expression of foreign genes following direct injection into fish muscle

We report here for the first time direct injection of genes into fish muscle in vivo. Plasmids used contain either SV40 early promoter, rabbit beta-cardiac myosin heavy chain promoter, human MxA promoter or an artificial promoter, fused to a chloramphenicol acetyltransferase (CAT) or beta-galactosidase reporter gene. CAT assays revealed that most gene constructs were highly expressed. Histochemical analysis showed that beta-galactosidase was strongly expressed at the site of injection within muscle fibres. This method provides an excellent system for testing expression of gene constructs, including those of mammalian origin, in fish muscle in vivo and has the potential for fish vaccination.