1. TRANSGENIC FISH PRODUCTION

2. An organism that has a foreign or modified gene transferred to its genome using the in vitro genetic techniques is called a genetically modified organism (GMO) or a transgenic organism. Transgenes can originate from phylogenetically distant organisms or from the same species. For the production of transgenic animal, a cloned gene is transferred into the fertilized egg before the completion of first cleavage. Scientists are seeking ways to genetically engineer fish and other seafood species to introduce or amplify economically valuable traits. Fish are of particular interest to researchers since many fish produce large quantities of eggs; those eggs, being external to the animal (as opposed to mammals that produce fewer eggs internally), make it relatively simple to insert novel DNA

3. Research on transgenic fish is currently under development for at least 35 species of fish worldwide, as well as for a variety of mollusks, crustaceans, plants, and marine microorganisms, for various purposes. Transgenic technology has been successfully used to develop fast-growing super-fish stocks for human consumption, to produce pharmaceuticals, to test water contamination in both developed and developing countries. Several laboratories now have GM fish with increased growth performance caused by extra copies of GH genes

4. A. Selection of species and genes For the aquacultural importance, Indian major carps, Common carp, Channel catfish, Chinese carps, Salmon, Trout and Tilapia are the best species for the transgenic project. Improvement of growth rate, imparting disease and environmental stress resistance are some important traits for transgenesis.

5. B. Reporter genes Reporter gene is defined as a gene whose products detects or marks the cells, tissues, organisms that express the gene from those that do not. Reporter genes isolated from prokaryotes, E. coli, are used in fishes- lac Z gene, Cat (Chloramphenicol Acetyl Transferase gene). Recently luciferase and green fluorescent protein are used.

6. C. Genes of interest 1. Growth hormone gene Growth is a complex biological process involving genetic, hormonal, nutritional and environmental factors. ‘Growth hormone’ (GH) is produced by the anterior lobe of the pituitary plays the key role. It increases growth by stimulating appetite and improving the food conversion efficiency. GH is a protein hormone having a molecular weight of about 22 kilodaltons. Transgenic fish carrying GH gene will produce growth hormone endogenously by passing the necessity of exogenous hormone treatment. GH gene has been cloned in some fishes either from the genomic library or from the cDNA library.

7. 2. Antifreeze protein genes Production of cold resistant fish variety is useful for establishing aquaculture industry in the temperate region, where water gets frozen during winter. The gene responsible for imparting cold resistance was cloned from winter flounder (Pseudopleuronectes americanus), which lives in the polar sea. This species avoids freezing of its blood even at –7  C temperatures by producing a set of anti-freeze proteins (AFP). AFP are produced in the liver and exported to the blood stream.

8. 3. Disease resistance Fish has poorly developed antibody dependent immunity. Efforts to produce disease resistance in fish stocks by transgenesis have begun recently. The potential of Rainbow trout lysozyme gene as a bacterial inhibitor was assessed in Atlantic salmon.

9. D. Techniques of gene transfer 1. Microinjection The most common method of gene transfer. Soon after fertilization the gene is microinjected into the cytoplasm since the egg nucleus is not visible in the fishes. Linearised DNA rather than circular DNA is injected for the greater probability of the former to get integrated into the host’s genome. Higher amount of DNA is used for cytoplasmic gene transfer than when it is injected to the pronucleus. Some species has softer chorion such as catfish, Zebra fish. Small volume of the solution 1-2 nl of DNA containing >10 7 copies should be injected. The rate of survival and integration of the transgene after microinjection varies widely in different species of fishes and in different batches of the same species.

10. 2. Electroporation It utilizes a series of short electrical pulses to make the membrane porous and permeable to DNA incorporation. Embryos and sperms can be electroporated. It is less labour intensive and does not require special expertise for gene transfer as needed in the case of microinjection. It is easier to do this in spermatozoa than in embryos, which possess tough chorion. The gene transfer efficiency and integration rate do not differ much between electroporation and microinjection methods. In zebra fish 0.1 milli second pulses of 125/cm for batches of 200 eggs.

11. E. Detection of transgene There are various ways and means to detect this. Most of them used southern blot and northern blot to detect the transgenes using a suitable probe (dot blot).

12. Glofish The GloFish is a patented brand of genetically modified (GM) fluorescent zebrafish with bright red, green, and orange fluorescent color.patentedgenetically modifiedzebrafishfluorescent The transgenic zebrafish (Danio rerio) expressing a red fluorescent protein from a sea anemone under the transcriptional control of the promoter from the myosin light peptide 2 gene of zebrafish.

13. Food safety of transgenic (GM) fish GM food safety depends on the nature of the gene, the transgene product it encodes and the resulting phenotype. Ethics and animal protection concerns allows the development of healthy and safe fish only. Transgenic fish have received extra copies of GH genes, resulting in only moderately raised levels of circulating GH. GH is a protein hormone which is degraded along with all other food protein.

14. Meat from fish modified with GH is regarded as completely safe for human consumption Concerns have been voiced of the possible risks of consumption of transgenes, their resulting protein, potential production of toxins by aquatic transgenic organisms, changes in the nutritional composition of foods, activation of viral sequences and allergenicity of transgenic products

15. Environmental impact of transgenic fish The possible impacts from the escape of GM organisms from aquaculture facilities are of great concern to some scientists and environmental groups. Critics and scientists predict that GM fish could breed with wild populations of the same species and potentially spread undesirable genes Escaped transgenic fish could harm wild fish through increased competition or predation. The consequences of such competition would depend on many factors, including the size of the wild population, the number and specific genetic strain of the escaped fish, and local environmental conditions.

16. FDA could require that only sterile GM fish be approved for culture in ocean pens. Fertilized fish eggs that are subjected to a heat or pressure shock retain an extra set of chromosomes. The resulting triploid fish do not produce normal eggs or sperm, and females do not exhibit maturation of the ovary or reproductive behaviors. Thus, all-female lines of triploid fish are the best current method to ensure non-breeding populations of GM fish.

17. Possible Benefits and Disadvantages of GM Fish and Seafood Biotechnology proponents maintain that genetic modification has many advantages over traditional breeding methods, including faster and more specific improvement of beneficial traits. Genetic modification allows scientists to precisely select traits for alteration, enabling them to create an organism that, for example, grows larger or faster or has a different nutritional content. Increased freeze resistance in fish could lead to the ability to grow freeze-resistant species in previously inhospitable environments, allowing aquaculture to expand into previously unsuitable areas.

18. Biotechnology proponents claim these advantages could translate into a number of potential benefits, such as reduced costs to producers, lower prices for consumers for edible fish and pharmaceuticals, and environmental benefits, such as reduced water pollution from wastes. M.ajority of consumers in the United States appear to have accepted GM food and feed crops, it is uncertain whether consumers will be as accepting of GM fish

19. Conclusion The future success and application of transgenic fish will depend upon by successful demonstration of a lack or potential lack of environmental risk, food safety, appropriate government regulation and labeling, public education and development of genetic sterilization for transgenic fish. Appropriate, well executed public education may be necessary to gain broad consumer acceptance of transgenic fish from an environmental standpoint and perhaps in relationship to how “organic” a transgenic fish may be.

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