TRANSGENIC FISH

Transgenic fish are produced by the artificial transfer of rearranged genes into newly fertilized eggs. Currently microinjection is the pref erred method, although the integration rates of transgenes are general ly low. A number of fusion genes, containing retrovirus sequences whic h direct integration, have been developed to enhance integration of tr ansgenes. Mass gene transfer methods are also being developed. These i nclude lipofection, particle bombardment, and electroporation of embry os and sperm cells. These methods are potentially useful for marine or ganisms such as crustaceans and molluscs as well as fish. In contrast to microinjection, which treats single cells individually, these metho ds can transfer genes into a large number of eggs at once. There is so me evidence to indicate successful integration and expression of trans genes transferred by the electroporation of embryos and sperm cells. G ermline transmission of transgenes has been observed through mating st udies, and in some cases the progeny express the new phenotype consist ently. However, germline transmission does not necessarily confirm sta ble integration of the transgene. There is evidence that transgenes ma y exist extrachromosomally. Transgenic fish are viewed as a useful mod el for the study of complex biological phenomena such as growth and di fferentiation, and as a fast track to the production of broodstock for the aquaculture industry. Current research focuses on the elucidation of the mechanisms controlling the regulation of gene expression. The use of transgenic fish for the isolation of developmental genes has ju st begun. Applications of transgenesis to broodstock development have been focused on the development of fish with accelerated growth, toler ance to low temperature, and disease resistance. However, before the r elease of transgenic fish into the environment, the possible impact on the environment must be assessed. There must be safeguards to protect the genetic diversities of the natural populations, and to conserve t he natural habitats.