As the great research progresses have been made in gene-transfer in fish, transgenic fishes are most likely to be put into the market on the near future. On the other hand, the behaviors of transgenes in transgenic fish are not fully understood just like those in other transgenic animals, so it is impracticable now to integrate a foreign gene into a specific site of the host genome and control its proper expression. Due to this, the process of generating homogenous transgenic fish is seriously inhibited. To find out the molecular mechanisms involved in the processes of transgene integration and inheritance, it is necessary to clone and analyze transgenes along with the sequence at integration site. In the present work, pMThGH-transgene and sequences flanking it have been cloned from a F4 hGH-transgenic red common carp, aiming at revealing evidences for transgene integration and inheritance, also the feature of sequences at functional integration site. Furthermore, the sequences of functional integration site can be used as molecular genetic markers for different transgenic fish lines, also can be severed as targeting sites for gene targeting in fish. Two kinds of traditional method, genomic DNA library screening and inverse PCR (IPCR), have been employed in cloning transgene and sequence of integration site. Apart from the present paper, there are only a few published reports about the cloning of a transgene along with flanking sequences from the DNA of transgenic animals. In some degree, this fact is due to the limitations of the application of traditional methods. Fortunately, a kind of simpler technique, plasmid rescue, has successfully employed to reisolate transfected genes from cell cultures. In the present study, the technique of plasmid rescue has been modified and used to recover transgene from transgenic fish for the first time. Results are described as follows: (1). Using a modified plasmid rescue technique, fifty transgnes were successfully recovered from the genomic DNA of a F_4 pMThGH-transgenic red common carp. (2). These recovered plasmids were classified into 4 types after double restriction with EcoRI and BamHI endonuclease. The restriction maps of these transgenes were constructed by digestion with 5 kinds of endonuclease. Only 1 type of transgene (18%) retains its original structure, whereas the other three types are very different from the original form and vary from each other on both molecular weight and physical maps. This implies that the sequences of most transgenes have been deleted and/or rearranged during integration and inheritance. Transgenes in F_4 transgenics are highly polymorphic. (3). The flank sequences in two kinds of transgene were subcloned into the pUC18 vector and sequenced. Sequencing results showed that the 5' untranslated region (5'UTR) of common carp β-actin gene flanked Type II transgene. It can be deduced that the core sequence of Type II transgene was located at 5'UTR of the host β-actin gene. This transgene was integrated into the host genome as single copy or at the end of transgene concatemers. The genomic sequence trapped by TypeIII transgene was homologous to the sequence of mouse tie2 gene. Part of flank sequence was detected in the genomic DNA of non-transgenic common carp by PCR and confirmed by Southern hybridization analysis. It is believed that TypeIII transgene was inserted as single copy into a genome site between the 5' flanking region and intron I of tie2-like gene. The relationship between transgene integration sites and levels of expression was extensively discussed. (4). Based on the results of Southern blot and transgene recovery with various endonuclease, it was confirmed that multiple copies of transgene were integrated into the fish genome as transgene concatemers. PCR result demonstrated that transgenes were arrayed in a head-to-tail manner within the concatemers. The junction fragment of transgene-transgene was amplified by PCR. Sequence aberrations, in a majority of insertion of single extraneous nucleotides, were observed at the transgene junction according to the result of sequencing analysis. The homology between the transgene junction and its corresponding region on pMThGH was lower than the expectation, with bases identity of 97.2%. The recognized site of BamHI was found at the joint of transgene-transgene. This fact strongly suggested that the ends of transgene had not been modified when transgenes were arrayed in a head-to-tail manner to form concatemers. It was also consistent with the result of Southern blot analysis. (5). Key techniques to recover transgene from genomic DNA of transgenic fish were pointed out in this paper. Further steps to improve the efficiency of transgene recovery were also proposed. Briefly, these findings reveal the molecular polymorphism and distinctive integration pattern of transgenes in F_4 transgenics. This study will substantially contribute to a better understanding of the mechanism of transgenes integration and inheritance.