The genetic stability and expression efficiency of exogenous genes in transgenic animals are closely related to integration site and copy number. In our laboratory, by transgenic manipulation and subsequent test crosses, we established an "all-fish" growth hormone (GH) transgenic common carp family that exhibits fast growth. In this present study, genome walking, real-time quantitative polymerase chain reaction, and fluorescence in situ hybridization techniques were applied to identify the integration characteristics of the exogenous grass carp GH gene in the transgenic common carp. The exogenous GH genes, in the form of two complete and one incomplete tandem repeats, were found to have integrated into an AT-rich region near the end of a chromosome pair. We hypothesize that the high efficiency of exogenous GH gene expression might be due to the low copy number in the genome and the AT-rich integration site.