Transgenesis in fish concerns the creation of modified or new fish genomes. This technology is still, in contrast to mammals, at an early stage of development. The basis of this technology is a gene transfer, which involves insertion of the DNA for a gene into the DNA of a recipient organism. The purpose of such manipulation is to improve the recipient organism. The new gene may confer faster growth of the fish or disease resistance. The main aim of most experiments was growth rate acceleration through introduction of novel growth hormone genes, and accelerated growth has been observed among produced transgenic common carp, northern pike and loach.
There are five steps in gene transfer. First, the gene must be identified and located in the organism in which it occurs naturally. Second, a copy of the DNA for the gene must be obtained. Third, DNA for the gene is cloned (produced in large quantities). Fourth, copies of the gene are inserted into a transfer vector, usually a bacterial plasmid. Bacterial plasmids are circular "minichromosomes" derived from bacteria. In the final step, the transfer vector with the gene is applied to the cells (usually the eggs or sperm of the fish) of the recipient organism. If the transfer is successful, at least one copy of the gene is integrated into the recipient's genome and expressed. It is then expected that the inserted gene will be passed to future generations of fish through the future gametes of the recipient.
The use of genetically engineered fish for aquaculture is less risky than their use in management of wild populations, because the effects of such fish on wild stocks, communities and ecosystems are still unknown. Genetically engineered fish require careful evaluation before their introduction into natural environments is considered. Biological characteristics (e.g. growth, food consumption rates, fertility, behaviour and longevity) of genetically engineered fish should be determined. Extensive field tests in carefully controlled environments are required in order to determine the ecological interactions between genetically engineered fish and natural communities. Genetically engineered fish that are released into natural environments should be sterile, at least until the biological and ecological uncertainties are resolved. Genetically engineered fish used for aquaculture will also require extensive evaluation. Of particular interest are the effects of genetic manipulations on fitness and commercially important characteristics (i.e. growth rate, food consumption and disease resistance). With such a new science, the problem once again is the lack of existing long-term studies and results for reference, hence no-once can answer give a guaranteed answer to this question. The future of such will probably be determined by national and international programmes, studies and agreements involving expert interest groups and scientists.
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