There are two ways of genetic modification in aquaculture. First, is genome or chromosome set manipulation. Generally, in every individual animal cell there are two sets of chromosomes (2 N), which represents the genetic material. During reproduction, both parents produce specific cells, the gametes, with only one set of chromosomes (1 N) in each cell. The gametes combine during fertilization of the embryo to contain two sets of chromosomes (2 N), one from each parent. In a method known as genome manipulation, haploid (1 N), triploid (3 N), tetraploid (4 N), gynogenotes (2 N - only maternal genetic material), androgenotes (2 N - only paternal genetic material) or polyploid hybrids can be produced.
In the second method, known as transgenesis, a separate gene or group of genes from a species is transferred to a fertilized embryo by injection of the foreign DNA (genes) into the nucleus of the embryo. In aquaculture, one of the most used foreign DNAs is the hormonegrowth gene. Usually, animals injected with such (known as transgenetic animals) show a much higher growth rate in comparison to non-injected specimens.
Transgenic organisms, mainly plants, can be used in the preparation of food. In the USA many grocery shelves contain cans of food with genetically manipulated components. Such genetically engineered food contains substances that were not part of the human food supply chain in the past. Thus, the problem is that no long-term studies exist to determine if they are truly safe for human consumption.
Genetic methods can also be used in restoration and conservation projects. It is used in preserving valuable genetic resources by means of application of modern genetic-biotechnological methods such as the androgenesis method. This method involves producing a "new generation" from paternal genetic material only. It is the most important method from an aquaculture point of view. Cryo-preserved sperm is collected in "gene banks". Due to the nature of fish eggs, cryo-preservation of fish embryos and eggs remain unsuccessful, however the cryo-preservation of sperm has been quite successful. During the studies on androgenesis in rainbow trout it was shown that an out-bred strain can be restored from cryo-preserved sperm through a two-step process, in which homozygous androgenetic diploids may be produced first, and different homozygous androgenetic diploids may then be crossed to restore heterozygosity and genetic viability.
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