A variety of gene constructs containing carp beta-actin regulatory sequences were tested for their ability to drive transient expression of the chloramphenicol acetyltransferase reporter gene in 3 fish cell lines: carp epithelial cells (EPC), rainbow trout hepatoma cells (RTH149), and rainbow trout fibroblasts (RTG2). The constructs showed a wide variation in their levels of expression, and there were significant differences in the effects of transcriptional elements in the 3 cell lines. Sequences that enhanced expression in EPC cells were inhibitory in RTH149 and RTG2 cells. All cell lines exhibited the presence of nuclear trans-acting factors that could bind to implicated transcriptional control elements. On the basis of the cell culture results, selected constructs were examined for activity in early carp development. Constructs active in embryos and fry were further tested and found to express transgenes in adult fish.